Great Lakes Avian Radar

Technical Report

Delta County, MI

Iosco County, MI

Huron County, MI

Fall 2012 Season

Biological Technical Publication

BTP-R3016-2017

U.S. Fish & Wildlife Service, Region 3

Funding Provided by the Great Lakes Restoration Initiative

U.S. Fish & Wildlife Service

Great Lakes Avian Radar

Technical Report

Delta County, MI

Iosco County, MI

Huron County, MI

Fall 2012 Season

Biological Technical Publication

BTP-R3016-2017

October 2017 

Principle Investigator: 

Jeff Gosse, Regional Energy Coordinator, USFWS Region 3 

Region 3 Authors:

Nathan Rathbun, Fish and Wildlife Biologist, USFWS Region 3

Rebecca Horton, Fish and Wildlife Biologist, USFWS Region 3

Tim Bowden, Fish and Wildlife Biologist, USFWS Region 3

Daniel Nolfi, Fish and Wildlife Biologist, USFWS Region 3

Erik Olson, Fish and Wildlife Biologist (GIS), USFWS Region 3

David Larson, Assistant Regional Energy Coordinator, USFWS Region 3

U.S. Fish & Wildlife Service, Region 3

Funding Provided by the Great Lakes Restoration Initiative

U.S. Fish & Wildlife Service Region 3
Corresponding Author:

Nathan A. Rathbun

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5182

Email: nathan_rathbun@fws.gov

Authors’ Complete Contact Information:

Jeffrey C. Gosse

U.S. Fish and Wildlife Service

Regional Energy Coordinator

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5138

Email: jeff_gosse@fws.gov

Timothy S. Bowden

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5197

Email: timothy_bowden@fws.gov

Rebecca L. Horton

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5196

Email: rebecca_horton@fws.gov

David J. Larson

U.S. Fish and Wildlife Service

Assistant Regional Energy Coordinator

(Retired)

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5336

Email: david_larson@fws.gov

Daniel C. Nolfi

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5195

Email: daniel_nolfi@fws.gov

Erik C. Olson

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist (GIS)

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5488

Email: erik_olson@fws.gov

Nathan A. Rathbun

U.S. Fish and Wildlife Service

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5182

Email: nathan_rathbun@fws.gov
Funding for this study was provided by the Great Lakes Restoration Initiative 

Disclaimer: The findings and conclusions in this article are those of the authors and do not 

necessarily represent the views of the U.S. Fish and Wildlife Service. The mention of trade names or 

commercial products in this report does not constitute endorsement or recommendation for use by 

the Federal government.

Key words: Great Lakes, migration, avian radar, wind energy, birds, bats, 

Lake Huron, Lake Michigan 

Recommended citation: 

Rathbun, N.A., R.L. Horton, T. S. Bowden, E. C. Olson, D. C. Nolfi, D. J. Larson, and J. C. Gosse. 2016. 

Great Lakes Avian Radar Technical Report Delta County, MI Iosco County, MI, and Huron County, MI Fall 

2012. U.S. Department of Interior, Fish and Wildlife Service, Biological Technical Publication FWS/BTPBTP-R3016-2017
ISBN-10 1-938956-09-5 Electronic ISBN-13 978-1-938956-09-6

Biological Technical Publications online: 

http://digitalmedia.fws.gov/cdm/search/collection/document/searchterm/Biological%20Technical%20Publications/field/collec/mode/exact/conn/and/order/nosort
 i

Table of Contents

List of Figures ......................................................................................................................................................... ii 

List of Tables .......................................................................................................................................................... v

Acknowledgements............................................................................................................................................... vi

Executive Summary................................................................................................................................................vii

Introduction............................................................................................................................................................. 1

 Objectives .................................................................................................................................................. 2

Methods.................................................................................................................................................................. 3

 Study Area and Site Selection ............................................................................................................. 3

 Equipment ...............................................................................................................................................6

 Radar Set Up and Data Collection....................................................................................................... 7

 Radar System Outputs .................................................................................................................................................... 7

 Data Processing and Quality Control ................................................................................................. 7

 Data Summary and Trends Analysis ................................................................................................. 10

Results .................................................................................................................................................................. 14

Upper Peninsula of Michigan - Green Bay, Lake Michigan ..................................................................14

 Qualitative Assessments .....................................................................................................................14

 Directional Trends ................................................................................................................................18

 Temporal Trends ..................................................................................................................................19

 Altitudinal Trends ................................................................................................................................ 24

Lower Peninsula of Michigan – Saginaw Bay, Lake Huron ................................................................. 35

 Qualitative Assesments ........................................................................................................................... 35

 Directional Trends ............................................................................................................................... 38

 Temporal Trends .................................................................................................................................. 39

Altitudinal Trends ................................................................................................................................ 47

Discussion ............................................................................................................................................................. 58

 Sampling Regime ................................................................................................................................ 58

 Site Comparison Considerations ....................................................................................................... 58

 Migration Patterns .................................................................................................................................59

 Flight Altitude ......................................................................................................................................60

 Radar Study Considerations ...............................................................................................................60

 Conclusions ............................................................................................................................................61

Literature Cited ......................................................................................................................................................62

Appendices .......................................................................................................................................................... 67

 Fall Summary Report ..........................................................................................................................68

 Percent Land Cover Associated with Study Sites and the 2011 

 National Land Cover Database Classification ..................................................................................70

 Corrected Density per Hour by Biological Period ...........................................................................72

 Comparison of Static and Corrected Density Estimates ............................................................... 74
ii

List of Figures

Figure 1. Locations where MERLIN Avian Radar Systems were deployed during the fall 2012 migration 

season. ............................................................................................................................................................................ 4

 

Figure 2. Land cover types (Jin et al. 2013) found within a 3.7 km radius of our West Delta County, Garden 

Peninsula, Iosco County, and West Huron County radar sites. .............................................................................. 5

Figure 3. Computer representation of the potential survey volume scanned by the horizontal and vertical

radars used by the U.S. Fish and Wildlife Service. .................................................................................................. 6

Figure 4. Clutter maps from vertical and horizontal scanning radars at study sites at our West

Delta County and Garden Peninsula study sites, during the fall 2012 migration season. ................................... 8

Figure 5. Clutter maps from vertical and horizontal scanning radars at study sites at our Iosco

County and West Huron County study sites, during the fall 2012 migration season. ......................................... 9

Figure 6. Schematic of the vertical scanning radar and standard front. .............................................................. 11 

Figure 7. A graphical representation of the structural volume of the vertical scanning radar within the

standard front. ............................................................................................................................................................. 13

Figure 8. Volume of 50-m altitude bands within the standard front as estimated with 

Monte Carlo integration. ............................................................................................................................................ 13

Figure 9. Images of tracks during one hour increments recorded by horizontal and vertical scanning

radars during a migration event at our West Delta County radar site. .............................................................. 15

Figure 10. Images of tracks during one hour increments recorded by horizontal and vertical scanning 

radars during a migration event at our Garden Peninsula radar site. ................................................................. 16

Figure 11. Target direction per hour during four biological periods during fall 2012 at our West 

Delta County and Garden Peninsula sites. .............................................................................................................. 18

Figure 12. Movement direction of targets for each night over the first part of the season. .............................. 19 

Figure 13. Hourly counts by horizontal and vertical radars from July 29 – September 1, 2012, West Delta

County. .......................................................................................................................................................................... 20

Figure 14. Hourly counts by horizontal and vertical radars from August 9 – September 1, 2012, Garden 

Peninsula. ..................................................................................................................................................................... 20

Figure 15. Box plots showing variability in target passage rate (targets/km/hr) during four biological 

periods for fall 2012 in West Delta County and Garden Peninsula. ..................................................................... 21

Figure 16. Mean hourly target passage rate (targets/km/hr) during fall 2012 at sites in West Delta County

and Garden Peninsula. ................................................................................................................................................ 22

Figure 17 Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in 

West Delta County and Garden Peninsula. ............................................................................................................. 22
Figure 18. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during fall 2012 at our West Delta County and Garden Peninsula radar sites. .................................................. 23

Figure 19. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during fall 2012 at our West Delta County and Garden Peninsula radar sites. ................................................. 24

Figure 20. Altitude profile of dawn, day, dusk and night targets at our West Delta County site. ..................... 26

Figure 21. Altitude profile of dawn, day, dusk and night targets at our Garden Peninsula site. ....................... 27

Figure 22. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume in 

West Delta County. ..................................................................................................................................................... 28

Figure 23. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume 

in Garden Peninsula. .................................................................................................................................................... 29

Figure 24. Altitude profile of target density below 400 meters at sites in West Delta County and 

Garden Peninsula. ...................................................................................................................................................... 30

Figure 25. Percent of nights when the maximum density (targets/1,000,000 m3/altitude band) 

or count (targets/altitude band) occurred within 50-m altitude bands at sites in West Delta County 

and Garden Peninsula. ................................................................................................................................................ 30

Figure 26. Percent of night hours when the maximum density (targets/1,000,00/m3/altitude band) 

or count (targets/altitude band) occurred within 50-m altitude bands at sites in West Delta County 

and Garden Peninsula. ................................................................................................................................................ 31

Figure 27. Mean hourly target height (m) during fall 2012 at our West Delta County and Garden

Peninsula sites. ............................................................................................................................................................ 32

Figure 28. Variation in flight altitudes based on target density (targets/1,000,000 m3/altitude band) 

at our West Delta County, Michigan site throughout the fall 2012 study period. .............................................. 33

Figure 29. Variation in flight altitudes based on target density (targets/1,000,000 m3/altitude band) 

at our Garden Peninsula, Michigan site throughout the fall 2012 study period. ................................................ 34

Figure 30. Images of tracks during one hour increments recorded by horizontal and vertical 

scanning radars during a migration event at our radar site in Iosco County. .................................................... 36

Figure 31. Images of tracks during one hour increments recorded by horizontal and vertical 

scanning radars during a migration event at our West Huron County radar site. ............................................ 37

Figure 32. Target direction per hour during four biological periods during fall 2012 at our Iosco County 

and West Huron County radar sites. ........................................................................................................................ 38

Figure 33. Movement direction of targets for each night over the second part of the season. ......................... 39

Figure 34. Hourly counts by horizontal and vertical scanning radars from September 6 - 

November 7, 2012 in Iosco County, Michigan. ........................................................................................................ 40

Figure 35. Hourly counts by horizontal and vertical scanning radars from September 2 – November 7, 2012

in Huron County, Michigan. ....................................................................................................................................... 41

iii
Figure 36. Box plots showing variability in target passage rate (targets/km/hr) during four 

biological periods for fall 2012 in Iosco and West Huron Counties. .................................................................... 42

Figure 37. Mean hourly target passage rate during fall 2012 at our Iosco County and 

West Huron County radar sites. ............................................................................................................................... 43

Figure 38. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) 

at our Iosco County and West Huron County radar sites during fall 2012. ........................................................ 44

Figure 39. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean)

during fall 2012 at our Iosco County and West Huron County sites .................................................................... 45

Figure 40. Comparison of nocturnal and diurnal target passage trends (based on a

moving 7-day mean) during fall 2012 at our Iosco County and West Huron County sites ............................... 46

Figure 41. Altitude profile at our Iosco County site. ............................................................................................... 48

Figure 42. Altitude profile at our West Huron County site. ................................................................................... 49

Figure 43. Mean hourly target height (m) during fall 2012 at our Iosco County and West Huron County

sites. ............................................................................................................................................................................. 50

Figure 44. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample 

volume at our West Huron County site during fall 2012. ....................................................................................... 51

Figure 45. Altitude profile of target density below 400 meters in at our sites in Iosco County 

and West Huron County during fall 2012. ............................................................................................................... 52

Figure 46. Percent of nights when the maximum density (targets/1,000,000 m3/ altitude band) or count 

(targets/altitude band) occurred within 50-m altitude bands at our Iosco County and

West Huron County study sites, during fall 2012. .................................................................................................. 53

Figure 47. Percent of night hours when the maximum density (targets/1,000,00/m3/altitude band) 

or count (targets/altitude band) occurred within 50-m altitude bands at sites in Iosco County 

and West Huron County. ............................................................................................................................................ 54

Figure 48. Figure 48 should read: Mean hourly target height (m) during fall 2012 at our Iosco County and 

West Huron County sites. .......................................................................................................................................... 55

Figure 49. Variation in flight altitudes based on target density (targets per million cubic m) at our West 

Huron County, Michigan site. .................................................................................................................................... 56

Figure 50. Variation in flight altitudes based on target density (targets per million cubic m) at our

Iosco County, Michigan site. ...................................................................................................................................... 57

Figure 51. Example of a hypothetical sampling schedule where data were collected once per 

week versus the actual continuous sampling schedule.......................................................................................... 59

iv
List of Tables

Table 1. Predominant land cover types found within a 3.7 km radius of the fall 2012 radar locations. ............ 4 

Table 2. Survey effort (hours) by vertical and horizontal scanning radars during fall 2012 at our radar sites

in West Delta County (WDC) and Garden Peninsula (GP). ...................................................................................14 

Table 3. Mean direction, angular concentration (r), and percentage of biological time periods 

with strong directionality (r ≥ 0.5) of targets during biological time periods at our West Delta County 

and Garden Peninsula sites. ........................................................................................................................................18

Table 4. Mean target passage rate (TPR) with standard deviations during four biological periods 

in West Delta County and Garden Peninsula during fall 2012. ............................................................................. 21

Table 5. Comparison of mean altitude (m) with standard deviations, median altitude, and altitude 

band that contained the maximum target density during four biological periods at our sites in 

West Delta County and Garden Peninsula during fall 2012. ................................................................................. 25

Table 6. Survey effort (hours) by vertical and horizontal scanning radars during fall 2012 at our Iosco

County (IC) and West Huron County (WHC) radar sites. .................................................................................... 35

Table 7. Mean direction, angular concentration (r), and percentage of biological time periods 

with strong directionality (r ≥ 0.5) of targets during biological time periods at our Iosco County 

and West Huron County sites during fall 2012. ...................................................................................................... 38

Table 8. Mean target passage rate (TPR) with standard deviations during four biological periods at our

Iosco County and West Huron County sites during fall 2012. .............................................................................. 42

Table 9. Comparison of mean altitude (m) with standard deviations, median altitude, 

and altitude band (50m bands) that contained the maximum target density during four 

biological periods at our sites in Michigan during fall 2012. ................................................................................. 47

v
Acknowledgements

This project would not have been possible without 

the funding provided through the Great Lakes 

Restoration Initiative for which we are very 

appreciative. We are grateful for the advice, 

technical assistance, and contributions of our 

collaborators Doug Johnson (U.S. Geological 

Service) and Kevin Heist (University of Minnesota). 

Jake Ferguson’s (University of Florida) statistical 

and programming expertise provided our model of 

the geometric shape of the radar beam. We thank 

the landowners that provided space for our radar 

units. We also want to thank other Service programs 

for their assistance during this season including 

Minnesota Valley National Wildlife Refuge, the 

Detroit Lakes Wetland Management District, and 

the East Lansing Field Office. This manuscript 

benefited from multiple external reviews and we 

thank those that contributed, which included: 

Katie Koch of the U.S. Fish & Wildlife Service, 

Amber Roth of the Midwest Landbird Migration 

Monitoring Network, and Bill Mueller and Brian 

Lenz of the Western Great Lakes Bird and Bat 

Observatory.

vi
Executive Summary

Global wind patterns help move millions of 

migrating birds and bats through the Great Lakes 

region where shorelines provide important stopover 

habitat. Shorelines are thought to concentrate 

migrants because they offer the last refuge near 

a geographic barrier and are likely used for 

navigation. Shorelines also offer areas attractive for 

wind energy development. With this potential for 

conflicting interests, more information is needed on 

the aeroecology of the Great Lakes shorelines. We 

used two avian radar systems to identify the activity 

patterns, timing, and duration of migration that 

occurred along the shorelines of the Great Lakes.

We split the season into two parts and surveyed 

two sites with avian radar systems in the Upper 

Peninsula of Michigan near the shorelines of Green 

Bay, Lake Michigan in August. We then surveyed 

two sites in the Lower Peninsula of Michigan near 

the shorelines of Saginaw Bay, Lake Huron for the 

remainder of the fall migration season (September 

through early November). While operating at 

each of the four sites, each of the avian radar 

systems tracked and recorded target (bird and bat) 

movements continuously. We calculated direction 

of movement, target passage rates, and altitude 

profiles for the air space above our study areas. 

We also developed a model of our vertical sample 

volume that allowed us to report an estimate of 

target density by altitude band.

Migration occurred at all of our study sites; however, 

by moving locations on the first of September, we 

likely missed the majority of fall migration at our 

Upper Peninsula study sites and only captured a 

few days of what appeared to be heavy migration.

We also were not able to document the duration 

of migration at the Upper Peninsula study sites; 

however, based on data collected at the study sites in 

the Lower Peninsula during the second part of our 

survey season, as well as from past seasons of data 

(Bowden et al. 2015, Horton et al. 2016c, Rathbun 

et al. 2016, Rathbun et al. 2017), we suspect that 

migration at these sites continued through at least 

October. The mean nocturnal passage rates were 

greater than the mean passage rates for dawn, 

day, and dusk combined at all of our locations. 

Nocturnal movement was generally orientated 

to the south for all sites. We also recorded other 

behaviors associated with migrants such as reverse 

migration, which was especially common at the sites 

in the Upper Peninsula, dawn ascent, and migrants 

over water returning to land at dawn. Peak density 

occurred between 100 - 350 m above ground-level; 

however, density may have been underestimated at 

higher and lower altitudes. 

The results of our research highlight the potential 

role of radar in implementing the Land-Based 

Wind Energy Guidelines and help identify areas 

where impacts to wildlife would be minimized. We 

documented migration activity in the air space above 

our study areas and suspect the density of targets 

at low altitudes may present conservation concerns. 

The data we collected showed the ebb and flow of 

migration across the sampling periods and that the 

nocturnal peaks continued through late October. 

Given the amount of time during which migration 

occurred, it seems that curtailing wind energy 

operations during nocturnal pulses could result in 

limited operational time along shorelines during the 

migration season. Combining the results of radar 

studies and fatality searches would greatly improve 

risk assessments and assist with the interpretation 

of standardized radar studies.

Avian radar is increasingly relied upon to perform 

surveys for pre-construction risk analysis. While it 

is recognized as an important tool, few regulatory 

agencies have experience implementing avian radar 

or otherwise recognize the strengths and limitations 

of the technology. This report highlights a number 

of considerations in the use of avian radar, and 

it reviews certain potentially confusing metrics 

In addition to providing information relevant to 

conservation in the Great Lakes region, the concepts 

we present in this report are widely relevant to 

reviews of avian radar studies, and we provide 

methods that identify components of migration such 

as:

n Nocturnal pulses

n Season length 

n Estimated density per altitude band

n Migrant behavior near a geographical obstacle

Given the rapid growth of the wind energy sector, 

our most effective conservation effort might be our 

ability to identify and avoid development in locations 

where migrants concentrate.

vii
viii
Introduction

Collectively, the Great Lakes constitute one of the 

largest bodies of freshwater on the planet, and they have 

a surface area of nearly 245,000 km2, and over 17,500 km 

of shoreline. Global wind patterns help to move millions 

of migrating birds and bats through the Great Lakes 

region (Rich et al. 2004, Liechti 2006, France et al. 2012), 

and globally recognized Important Bird Areas are often 

located on lake shorelines (Audubon 2013). Migrants 

passing through the region concentrate near shorelines 

(Ewert et al. 2011, Peterson and Niemi 2011, Buler 

and Dawson 2012, France et al. 2012), which provide 

important stopover habitats, or areas that are used 

temporarily for refueling, rest, and protection while 

en route to their breeding grounds. Compared with 

inland areas, these shorelines offer increased foraging 

opportunities relative to inland areas (Smith et al. 2004, 

2007, Bonter et al. 2007, 2009) and may serve as visual 

cues for navigation or as refuges for migrants before or 

after they cross open water (Buler and Moore 2011). 

Due to their location and size, the Great Lakes 

likely represent a geographic obstacle that migrants 

must cross or avoid based on the environmental and 

physiological conditions at the time they encounter 

the obstacle (Faaborg et al. 2010, Schmaljohann et 

al. 2011). For migrants that rely on powered flight, it 

is more efficient to make several short flights than a 

single long flight because of the cost of carrying high 

fuel loads (Alerstam 1990), and this may be one reason 

why migrants partially circumnavigate the Great Lakes 

despite being physiologically capable of crossing them 

(Alerstam 1990, 2001, Ruth 2007). Thus, the decision to 

cross likely represents a trade-off between minimizing 

costs (e.g., energy and time) and exposure to risk factors 

(e.g., predation and fatigue) associated with migration 

(McGuire et al. 2012a). Shorelines offer refuge when 

conditions do not favor flights over water. 

When challenged by an obstacle, migrants may 

temporarily reverse or deviate from seasonally 

appropriate flight directions or return to land to delay 

or recover from a crossing (Bruderer and Liechti 

1998, Akesson 1999, Ewert et al. 2011). Schmaljohann 

and Naef-Daenzer (2011) found that birds managing 

low fuel loads and/or unfavorable weather conditions 

returned to the shoreline habitat rather than continue 

across open water in the direction of migration. For 

bats, the migrants varied in their choice to cross over 

or circumnavigate lakes above the shorelines, and 

a number of long distance migrants use torpor to 

postpone migration in unfavorable conditions (McGuire 

et al. 2012b). These behavioral responses as well as 

the need to use stopover habitat during migration 

likely contribute to the increased use of shorelines 

and demonstrate the importance of these areas for 

conservation. 

Migrants concentrated along shorelines can be very 

mobile. In addition to using the shoreline habitats for 

immediate refueling and rest, migrants make broadscale flights between habitat patches, explore wind 

conditions, and orient themselves for migration. For 

example, radio-tagged bird and bat migrants on the 

north shore of Lake Erie made repeated movements 

between habitat patches, with individual birds and bats 

relocating as far as 18 and 30 km from their capture 

site, respectively, prior to resuming migration (Taylor 

et al. 2011). Nocturnal migrants, such as warblers and 

other Neotropical species, regularly engage in morning 

flights along shorelines (Wiedner et al. 1992). These 

flights typically occur within two hours of sunrise 

and likely represent reorientation along a geographic 

obstacle or movements between stopover habitats (Able 

1977, Moore et al. 1990, Wiedner et al. 1992). Flights 

of this nature often occur above the tree line (Bingman 

1980) but at heights lower than those associated with 

nocturnal migration (Harmata et al. 2000, Mabee and 

Cooper 2004, Newton 2008). 

Migrants have also been observed initiating nightly 

exploratory flights at stopover sites (Schmaljohann 

et al. 2011), and these flights are considered normal 

activities aimed at calibrating internal compasses and 

testing the wind speed and direction aloft. Migrants also 

follow north-south oriented shorelines en route to their 

destinations (Buler and Dawson 2012), whereas eastwest oriented shorelines may be used to circumnavigate 

open water or find narrow points for crossing (Alerstam 

2001, Diehl et al. 2003, France et al. 2012). Additionally, 

migrant birds may change their altitude many times 

over the course of a nocturnal migratory flight (Bowlin 

et al. 2015). Cumulatively, these activities define an 

area of use near lake shores and include a variety 

of movements and altitudes for landscape-level, 

exploratory, and migratory flights. However, these 

activities may increase the risk of collision with tall 

structures, such as buildings, communication towers, or 

wind turbines. 

Great Lakes Avian Radar - Fall 2012 1
Migrant populations may experience the greatest 

mortality pressure during migration (Newton 2006, 

2007; Sillett and Holmes 2002, Diehl et al. 2014), and the 

negative ramifications of compromised stopover habitat 

are becoming increasingly clear (Sillett and Holmes 

2002, Mehlman et al. 2005, Faaborg et al. 2010). Shoreline 

habitats along the Great Lakes are subject to pressures 

from urban and energy development, land conversion, 

and environmental contamination, which may limit habitat 

availability or reduce habitat quality (France et al. 2012). 

Of further concern is the devastation of hibernating 

bat populations by White-nose Syndrome, which has 

increased the need for identifying conservation areas 

as several of these species face extirpation in the Great 

Lakes region (Turner et al. 2011). The increased number 

of wind energy installations within the U.S. is further 

devastating bat populations by causing high numbers of 

fatalities to long-distance migratory tree bats (Kunz et 

al. 2007a, Cryan 2011, Arnett and Baerwald 2013, Hayes 

2013, Smallwood 2013). In response to such factors, 

substantial efforts are being made to identify and protect 

stopover habitat along the shorelines of the Great Lakes 

(Buler and Dawson 2012, Ewert et al. 2012, France et al. 

2012, Johnson, 2013), although careful planning is needed 

to balance the demands between increased renewable 

energy development to mitigate climate change and the 

conservation of migratory species. 

There is a national movement towards supplying 20% 

of the end-use electricity in the U.S. market by wind 

power by 2030 (U.S. D.O.E. 2008, 2015) and 35% by 2050 

(U.S. D.O.E. 2015). As of 2012, wind energy installations 

were on target to achieve the 2030 goal (AWEA 2015), 

which would represent a nearly five-fold increase in 

wind energy capacity over the next 15 years (Loss et al. 

2013). Coinciding with this national effort, wind energy 

development is increasing within the Great Lakes 

region, where windy shorelines are attractive areas for 

turbine placement (Mageau et al. 2008, Great Lakes 

Commission 2011). However, utility-grade wind facilities 

have been associated with mortality events in migrating 

vertebrates (Newton 2007, Arnett et al. 2008, Smallwood 

and Thelander 2008), and chronic fatalities across the 

U.S., particularly in bats, have become a concern (Timm 

1989, Johnson 2005, Arnett and Bearwald 2013, Hayes 

2013, Smallwood 2013). For example, approximately 75% 

of all bat mortalities occur in three species of long-distance 

migratory bats that are impacted by wind energy facilities 

(Cryan 2011, Kunz et al. 2007a, Arnett and Baerwald 

2013), and these migrants, the hoary bat ( Lasiurus 

cinereus), eastern red bat (Lasiurus borealis), and silverhaired bat (Lasionycteris noctivagans), typically account 

for the majority of bat fatalities at wind facilities in the 

Upper Midwest (Arnett et al. 2008). Three Wisconsin 

studies found high fatality rates for these same migrant 

species as well as substantial fatalities in the little brown 

bat (Myotis lucifugus) and big brown bat (Eptesicus 

fuscus) (Gruver et al. 2009, BHE Environmental 2010, 

Grodsky et al. 2012), although the presence of major 

hibernacula in the vicinity of wind facilities may have 

influenced the results. Additionally, low reproductive 

rates inhibit the ability of bats to rebound from population 

declines (Racey and Entwistle 2000), which have already 

begun in several species (Kunz et al. 2007a, Cryan 2011). 

The cumulative impacts on migratory birds and bats 

are a concern that will increase with the growth of wind 

energy if methods to avoid or minimize mortality events 

are not implemented. A number of promising conservation 

measures have been proposed to reduce mortality levels, 

but the greatest benefit to the conservation of migrants 

might lie in our ability to identify and avoid future growth 

in locations where migrants concentrate. 

To help meet the needs of both renewable energy 

development and wildlife conservation communities, 

we established this project to identify the activity 

patterns, temporal patterns, and magnitude of migration 

occuring along the shorelines of the Great Lakes.

Since bats and many bird species migrate during the 

night throughout the spring and fall, documenting the 

migration is challenging because observing sporadic 

nocturnal movements is difficult. We used a combination 

of techniques to address this problem. We primarily used 

two avian radar units that simultaneously scanned the 

horizontal and vertical planes 24 hours per day, and we 

used automated ultrasonic/acoustic monitors to record 

and bat calls. We chose radar because of its ability to 

collect data on migrants at long range, to return data both 

at day and night, and to provide an alternative metric to 

our acoustic monitoring program, which has different 

strengths and weaknesses (Horton et al. 2015). The results 

of our acoustic monitoring study will be forthcoming in a 

separate report. Avian radar has been shown to reliably 

track targets that fly through its detection area, although 

the specific target counts are not indicative of true 

population counts (Gerringer et al. 2015). Migration traffic 

on radars has been shown to correlate with the density 

of birds in stopover habitat during the day (Horton et al. 

2016a), indicating that migrants using the airspace are 

also using stopover habitat in the area. 

Objectives

Our objectives for the portion of the study we are 

reporting on included the following:

n Monitor locations along the shorelines of 

 Lake Michigan and Lake Huron using a 

 consistent methodology;

n Maintain an archive of continuously recorded 

 radar data during the fall migration season;

n Identify the activity patterns captured by radar 

 that are diagnostic of migration;

n Document changes in the behavior of migrants 

 under varying conditions and during different 

 parts of the season.

2 Great Lakes Avian Radar - Fall 2012 
Methods

Study Area and Site Selection

During the fall 2012 season, we selected four sites for 

radar placement. Two sites were located in the Upper 

Peninsula of Michigan, and two sites were located in 

the Lower Peninsula of Michigan (Figure 1). We looked 

for sites located approximately 0.75 – 3 km from the 

shoreline in order to monitor airspace above inland, 

shoreline, and lake areas as well as to investigate 

movement across large bays. 

Both of the sites located in the Upper Peninsula were 

in Delta County. Our “West Delta County” site was 

on the western side of Green Bay, south of Escanaba. 

This site was at 45.6245° N, -87.2274° W and was 

approximately 175 m above sea level and 1.5 km from 

the nearest shoreline. The radar was placed in the 

middle of a grassy field, in an area where, according 

to our analysis using Esri ArcGIS software and the 

2011 National Land Cover Database (Jin et al. 2013), 

woody wetlands and open water were the predominant 

land cover types within range of the radar unit (Table 

1, Figure 2, Appendix 2). Our “Garden Peninsula” site 

was located along the eastern side of Green Bay, in 

approximately the center of the Garden Peninsula at 

45.7419° N, -86.5680° W. This site was approximately 

180 m above sea level and 2.6 km from the nearest 

shoreline (Portage Bay). Woody wetlands and 

evergreen forest were the predominant land cover 

types present within the range of the radar unit at this 

study site (Figure 2).

The two sites in the Lower Peninsula were on opposite 

sides of Saginaw Bay, in Iosco and Huron Counties.

Our “Iosco County” site was on the northern side of 

Saginaw Bay, south of Tawas City. This site was at 

44.1852° N, -83.5665° W and was approximately 188 m 

above sea level and 0.75 km from the nearest shoreline. 

The radar was placed in a non-active area of a gypsum 

mine where open water and woody wetlands were 

the predominant land cover types within range of the 

radar unit (Figure 2). The second site, “West Huron 

County,” was on the southern side of Saginaw Bay, 

west of Sebewaing at 43.7999° N, -83.3955° W and was 

approximately 181 m above sea level and 2.8 km from 

the nearest shoreline. Cultivated crops constituted the 

major land cover type present within the range of the 

radar unit at this study site. Major cultivated crops in 

this area of Michigan are field beans, sugar beets, corn, 

and wheat (Huron County, 2015).

Selection of radar sites was achieved by examining 

areas using aerial imagery in order to identify areas 

near the shoreline. Areas were considered suitable 

based on distance to shoreline and distance to forest 

and man-made structures. Once suitable areas were 

identified, biologists contacted property owners to 

obtain permission to visit their land for site visits and 

radar placement, in order to assess potential sites. 

This assessment included evaluating the land use, 

line of sight for the radar units, and accessibility for 

placement. If additional locations that were not initially 

identified were discovered during site visits, they were 

evaluated as well.

Great Lakes Avian Radar - Fall 2012 3
Figure 1. Locations where MERLIN Avian Radar Systems were deployed during the fall 2012 migration 

season. The basemap is the intellectual property of Esri and is used herein under license. Copyright © 2014 

Esri and its licensors. All rights reserved.

Table 1. Predominant land cover types found within a 3.7 km radius of the fall 2012 radar locations.

Land Cover Class

Percent Land Cover

West 

Delta 

County

Garden 

Peninsula

Iosco 

County

West 

Huron 

County

Cultivated crops/Hay pasture 3% 21% 5% 61%

Deciduous forest 6% 10% 10% 6%

Deveoloped1 4% 4% 8% 6%

Emergent herbaceous wetlands 2% 1% 7% 6%

Evergreen Forest 7% 18% 4% 0%

Mixed Forest 8% 10% 2% 0%

Open water 24% 7% 35% 10%

Other2 7% 8% 10% 1%

Woody wetlands 39% 22% 19% 9%

1 Includes low, medium, and high intensity development and developed open space.

2 Includes barren land, herbaceous, and shrub/scrub.

4 Great Lakes Avian Radar - Fall 2012 
Figure 2. Land cover types (Jin et al. 2013) found within a 3.7 km radius of our West Delta County, Garden 

Peninsula, Iosco County, and West Huron County radar sites.

Great Lakes Avian Radar - Fall 2012 5
Equipment

We used two model SS200DE MERLIN Avian 

Radar Systems (DeTect Inc., Panama City, FL) to 

document migration movements. These systems 

were selected because they are self-contained mobile 

units specifically designed to detect, track, and 

count bird and bat targets. Each system employed 

two marine radars that operated simultaneously, one 

that scanned the horizontal plane while the other 

scanned vertically (Figure 3). Additionally, each unit 

contained four computers for real-time automated 

data processing and a SQL server for processed 

data storage and review. The units were configured 

with a wireless router to allow remote access to the 

computers and automated status updates.

Description of radars. The solid state marine radar 

antennas (Kelvin Hughes, London, UK) employed 

by our systems were 3.9 m in length, with 170 

W peak power, S-band (10 cm) wavelength, and 

2.92 – 3.08 GHz frequency range, and they were 

configured to operate with both short and medium 

pulses (0.1 and 5 microseconds, respectively). The 

horizontal radar was also equipped with Doppler to 

help filter stationary targets. The radars emanated 

a fan-shaped beam that had an approximate 1° 

horizontal and 25° vertical span when operated in 

the horizontal plane. The S-band radar was selected 

because the longer wavelength is less sensitive 

to insect and weather contamination than that of 

X-band (3 cm wavelength) antenna (Bruderer 1997). 

It is also less sensitive to signal attenuation from 

ground clutter such as vegetation and structures 

(DeTect Inc., unpublished data, 2009). The radars 

spun perpendicular to each other at a rate of 20 

revolutions per minute and were synchronized so 

as not to emit over one another. The horizontal 

scanning radar (HSR) was affixed to a telescoping 

base that was raised to approximately 7 m above 

ground for operation. This radar rotated in the x-y 

plane with a 7° tilt to reduce the amount of ground 

clutter included within its view. While the radar had 

the capability to scan large distances, we selected 

a 3.7 km range setting for data collection in order 

to have higher resolution and to identify smaller 

targets such as passerines and bats. The HSR was 

primarily used to provide information on target 

direction. The vertical scanning radar (VSR) rotated 

in the x-z plane and scanned a 1° x 25° span of the 

atmosphere. We selected a 2.8 km range setting 

for this radar for increased resolution and used the 

VSR to provide information on the number and 

height of targets. 

Weather Station. Each system was equipped 

with a weather station (Davis Vantage Pro 2, 

Hayward, CA) that recorded wind speed and 

direction, humidity, temperature, precipitation, 

and barometric pressure. These weather data were 

summarized and stored every five minutes. The 

anemometer was attached to the radar unit and 

measured wind speed at a height of approximately 

six meters above ground level.

Figure 3. Computer representation of the potential survey volume scanned by the horizontal and vertical 

radars used by the U.S. Fish and Wildlife Service. Graphic provided by DeTect, Inc.

6 Great Lakes Avian Radar - Fall 2012
Great Lakes Avian Radar - Fall 2012 7

Radar Set Up and Data Collection

The radar systems were deployed to the Upper 

Peninsula of Michigan during the last week of 

July; however, due to radar malfunction full data 

collection did not begin until early August. Data 

collection continued through September 1 in the 

Upper Peninsula. We then moved to two new sites 

in the Lower Peninsula of Michigan, where data 

collection occurred from the first week of September 

through the first week of November.

Establishing radar systems at a selected site 

involved several activities including orienting the 

VSR, micro-site selection, and adjusting to ensure 

adequate information was captured. We anticipated 

a primarily southbound direction of migration 

during the fall season and orientated vertical 

scanning radars to an angle that was slightly off 

of perpendicular to the anticipated direction of 

traffic. This orientation was a compromise between 

a perpendicular angle that would intercept the 

greatest number of targets (birds or bats) and a 

parallel angle that would maximize the amount of 

travel time within the radar beam. The orientation 

was also influenced by micro-site selection. Microsite selection is important in that positioning the 

radar can affect the amount of interference from 

ground clutter or other sources of noise. In our 

study, if large areas were obstructed from the 

radar’s view or if substantial amounts of clutter 

impeded data collection, the systems were rotated 

incrementally to improve the radar’s view and/or 

reduce interference. 

Once a position was established, clear-air thresholds 

and the radar’s built-in sensitivity time control 

(STC) filters were employed to reduce small nontarget returns and improve tracking of distant 

targets. These settings are needed as an object 

reflects more energy at close range than it does 

when it is further from the radar. For example, an 

object at a 50 m range will return about 16-times 

more energy than when it is at 100 m range 

(Bruderer 1997, Schmaljohann et al. 2008). To 

further improve the data collection, clutter maps 

were generated using 60-scan composite images 

(Figures 4-5) during time periods with low biological 

activity to identify areas with constant returns 

(white areas) that were not biological targets, such 

as tree lines, fencerows and buildings. These areas 

were assigned a reflectivity threshold that precluded 

the constant returns from being included in the data, 

thus reducing our ability to detect targets in these 

areas. 

Following this initial set up, MERLIN software was 

adjusted to fit the site conditions. The MERLIN 

software provided real-time processing of raw 

radar data to identify and track targets while 

excluding non-targets and rain events. However, 

the parameters used by the tracking software 

required adjustments to account for site specific 

conditions and biologists established settings with 

the goal of minimizing inclusion of non-targets while 

maximizing cohesive tracks of targets.

Processed data were stored in an Access database 

and transferred daily to a SQL database where they 

were stored and later queried for data analysis.

Despite the radar system’s ability to be operated 

remotely for extended periods of time, biologists 

remained on site during the data collection period 

to ensure continuous function, monitor raw 

(unprocessed analog radar returns) and processed 

radar outputs, provide routine maintenance (such as 

fueling and oil changes), and manage data storage.

In addition to processed data, we maintained all raw 

radar data for potential reprocessing. Raw radar 

data were temporarily stored in the field on 2 TB 

external hard drives and regularly transported 

back to the USFWS Regional Office (Region 3) 

on ruggedized external drives where data were 

transferred to long term tape storage. 

Radar System Outputs

The MERLIN software generated more than 

30 measurements to describe target size, shape, 

location, speed, and direction of movement. These 

data were of the same type used by biologists when 

identifying biological targets on a radar screen 

(DeTect Inc., unpublished data, 2009), and this 

information was stored to the database for later 

analysis. To reduce potential false tracking, the 

MERLIN tracking algorithm removed tracks with 

fewer than five observations. As well, an automated 

filter was used to remove sectors of the sample 

volume that were dominated by rain. 

In addition to storing target attribute data, the 

DeTect software outputs included a two-dimensional 

digital display of targets being tracked in real-time 

and static images of tracked targets over a specified 

period of time (Trackplots) for both vertical and 

horizontal radars. During each site check, we viewed 

the real-time digital display to ensure that it was 

consistent with the raw radar display, and we later 

viewed 15-minute and 1-hour Trackplots to assess 

the target direction and height during the previous 

day’s activity.

Data Processing and Quality Control

Prior to the data analysis, the data processed by 

the MERLIN software were further evaluated for 

potential contamination by non-targets. Although 

an automated rain filter was used, it did not 

remove all of the rain from the recorded outputs 

during certain time periods. Additionally, insects 

and other forms of transient clutter may have 
Figure 4. Clutter maps from vertical (left) and horizontal (right) scanning radars at study sites at our West 

Delta County (top) and Garden Peninsula (bottom) study sites, during the fall 2012 migration season. Brighter 

areas represent static returns from stationary objects, such as tree lines and fencerows. Target detection may 

be obscured in these areas because of obstructions from the objects.

West Delta County Clutter Maps

Garden Peninsula Clutter Maps

8 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 9

Figure 5. Clutter maps from vertical (left) and horizontal (right) scanning radars at study sites at our Iosco 

County (top) and West Huron County (bottom) study sites, during the fall 2012 migration season. Brighter 

areas represent static returns from stationary objects, such as tree lines and fencerows. Target detection 

may be obscured in these areas because of obstructions from the objects.

Iosco County Clutter Maps

West Huron County Clutter Maps
been recorded during data collection. Therefore, 

biologists reviewed all of the data in 15-minute 

time increments and removed the time periods that 

were dominated by rain, although there were no 

time periods dominated by other forms of transient 

clutter that needed to be removed. 

We relied on visual inspections of the track patterns 

to discern contamination events. Rain and insect 

events form diagnostic patterns (Detect Inc., 

personal communication, 2011), and time periods 

with these types of track patterns can be removed. 

Unknown contamination that mimicked the patterns 

of desired targets was not removed from the 

database and contributed to the error associated 

with the indices. In addition, we evaluated initial 

counts by generating a time series of the variation 

in the number of targets per hour throughout the 

season for the HSR and VSR radars. In general, 

the HSR and VSR hourly counts were positively 

correlated with higher HSR counts, and in situations 

where the VSR counts were higher than the HSR 

counts or where the peak counts appeared to be 

outliers, the data were further investigated for 

evidence of contamination or potential issues with 

radar performance. On the rare occasions when 

time periods with anomalies appeared to represent 

artifacts that were unrelated to target movement 

(e.g., rain events, insects, or data processing errors), 

these periods were removed from further analysis.

Once the contaminated time periods were removed, 

we summarized the data using SQL queries 

provided with the MERLIN radar system. Data 

from the HSR were used to calculate hourly counts 

and target movement direction. All targets within 

3.7 km of the radar unit were included in the 

analysis. Data from the VSR were used to calculate 

hourly counts and height estimates, and these data 

were truncated to a 1-km front, or “standard front”. 

We adopted this sampling technique as it is the 

method used by the manufacturer of the MERLIN 

units (DeTect Inc., unpublished data, 2009) and 

has also been used by other researchers (Lowery 

1951, Liechti et al. 1995, Kunz et al. 2007b). The 

standard front was defined by a volume of space 

that extended 500 m to either side of the radar 

and continued up to the maximum height of data 

collection (2800 m) (Figure 6). Counts were further 

segregated into four biological time periods: dawn, 

day, dusk, and night. Dawn represented 30 minutes 

before sunrise to 30 minutes after sunrise; day 

represented 30 minutes after sunrise to 30 minutes 

before sunset; dusk represented 30 minutes before 

sunset to 30 minutes after sunset, and night 

represented 30 minutes after sunset to 30 minutes 

before sunrise.

Data Summary and Trends Analysis

We used the processed data to assess the activity 

patterns associated with migration. Horizontal 

Trackplots were viewed to identify changes in 

activity and investigate the behaviors of the 

migrants, such as reverse migration (Akesson 1999) 

and migrants moving toward the shore at dawn, 

and vertical Trackplots were viewed to investigate 

changes in activity, such as dawn ascent (Myres 

1964, Diehl et al. 2003). Target counts represented 

abundance, and we used these indices to identify 

directional, temporal, and altitudinal trends.

 

Directional Trends. The mean angle and 

concentration (r) of the target movement directions 

were analyzed following the methodology for 

circular statistics (Zar 1999) included in the DeTect 

SQL queries. The angular concentration value has 

a value of 1 when all of the angles are the same 

and a value of 0 when all of the angles cancel each 

other out, indicating that there is no predominant 

direction of travel (e.g., if 50% of the vectors 

are 180° and 50% are 360°, then no direction is 

predominant because there were as many targets 

heading south as there were heading north). We 

anticipated a generally southward direction of 

movement by the nocturnal targets during the fall 

migration season and reported the mean direction 

and the percent of nocturnal targets that traveled in 

a direction between southwest and southeast (112.5° 

– 247.5°). We used radial graphs to plot the number 

of targets per eight cardinal directions (i.e., eight 

groups centered on N, NE, E, SE, S, SW, W, and 

NW) during the four biological time periods (i.e., 

dawn, day, dusk, and night). 

Temporal Trends. We plotted the counts of targets 

per hour processed by the MERLIN software for 

both the HSR and VSR antennas as a time series 

to identify pulses of nocturnal activity, the duration 

of the season, and changes in activity patterns over 

time. The HSR and VSR radars have different 

strengths that complement one another and were 

plotted together. The HSR index tracks low flying 

targets in a 360° span around the radar unit, and 

compared with the VSR, detection is unaffected by 

the target’s direction of travel, although the HSR 

index is much more affected by ground clutter, 

which impacts target detection and tracking, and 

errors caused by ground clutter lead to both underand over-counting. Targets blocked by ground 

clutter may not be counted, and targets that fly in 

and out of areas with ground clutter may be counted 

multiple times. Such issues lead to HSR counts that 

are more influenced by site characteristics relative 

to the VSR counts; however, the HSR index better 

captures targets under certain conditions, such as 

when targets are primarily at low elevations and/

or traveling parallel to the VSR. The HSR is also 

10 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 11

more susceptible to beam-bending from dynamic 

atmospheric conditions relative to the VSR, which 

presents minimal beam refraction primarily 

because of its orientation. The VSR index was used 

to track targets captured within the standard front, 

and it exhibited more consistent detection than 

the HSR because it mostly tracked against clear 

air except in the lowest altitude bands. Detection 

by the VSR index was affected by target direction 

and distance from the radar (Bruderer 1997, 

Schmaljohann et al. 2008), and it was impacted 

by ground clutter, particularly at low elevations. 

Plotting these indices together provided a more 

comprehensive understanding of changes in target 

activity over time.

We used the VSR index to calculate the target 

passage rate (TPR), which is the number of targets 

Figure 6. This schematic depicts the vertical scanning radar beam from two different views and pictures of 

the radar unit associated with those views. The top left graphic identifies the standard front used for data 

analysis, which extends to 500 m on either side of the radar and up to a height of 2800 m. In this graphic, the 

radar is situated at the bottom center, and the red dashed lines represent the lateral limits of the standard 

front. In the top right graphic, the radar rotation is suspended so that the beam is emitting directly upward; 

this view is an approximation of the beam dispersion as it travels away from the radar unit (schematic not 

drawn to scale).
per standard front per hour, using the DeTect 

SQL queries, and hour intervals with less than 

30 minutes of recording time were omitted from 

this calculation. For example, after removing all of 

the hours with less than 30 minutes of clean data, 

the nocturnal TPR for a given night (biological 

time period) was calculated by dividing the target 

count by the number of nighttime minutes and 

multiplying the value by 60 to yield the number of 

targets per hour during that night. We extended 

this metric to the season and calculated the mean 

TPR for the four biological time periods and hours 

of the season. The mean nocturnal TPR for the 

season is the sum of the night TPRs divided by 

the number of nights sampled. Similarly, the mean 

hourly TPR for the season is the sum of the TPRs 

for an hour-long period divided by the number 

times that hour was sampled. We also calculated 

mean nocturnal (night biological period) and 

diurnal (day biological period) TPR weekly during 

the sampling period using two methods. First, to 

demonstrate the variability among the sampled 

weeks, we divided the sum of the TPRs for a week 

(nocturnal or diurnal) by seven and reported the 

weekly mean TPR and its standard deviation. 

Second, to better illustrate the nocturnal and 

diurnal trends in TPR across the season, we plotted 

7-day moving TPR means as line graphs. 

Altitudinal Trends. The DeTect SQL queries 

were used to estimate the height of the targets 

tracked within the standard front from the VSR 

data. The height estimates were calculated based 

on the range and bearing of the target location 

with the largest radar echo and reported as the 

height above the ground as measured at the radar 

unit; this measurement did not consider changes 

in topography across the landscape. We used these 

estimates to calculate the mean altitude of the 

targets above the ground according to biological 

time period and hour, and we reported the mean 

and median altitudes for the season. 

Density per Altitude Band. In order to provide 

information on the density of targets per 50-m 

altitude band per hour within the standard front, 

we first estimated the volume of the radar beam’s 

approximate geometric shape. The width of the 

radar beam expanded as it traveled from the 

radar, resulting in increased survey volume with 

distance from origin. The shape of the survey 

volume contained the space in which targets had 

the potential of being detected and represented 

one of several considerations that define the 

realized or actual survey volume (Bruderer 1997, 

Schmaljohann et al. 2008). We calculated the volume 

contained by the shape of the radar beam and 

report the density of targets (targets/1,000,000 m3) 

per 50-m altitude band per hour for each biological 

period. This was calculated by dividing the number 

of targets per volume of an altitude band by the 

number of minutes with clean (uncluttered) data 

during the biological time period of interest and 

multiplied by 60. 

To estimate the volume of the 50-m altitude bands 

that were constrained by the standard front, we 

used Monte Carlo integration (Press et al. 2007), 

which is described in detail elsewhere (manuscript 

in preparation) and summarized here. The volume 

contained by the shape of the radar beam was 

calculated using spherical coordinates and multiple 

integration. However, subjecting this volume to 

Cartesian constraints (i.e., the standard front and 

the altitude bands) complicated the calculation, 

so the volume bands were more easily estimated 

using Monte Carlo integration, which is a method 

used to calculate an unknown volume by enclosing 

it in a known volume and saturating the space with 

random points. Monte Carlo integration requires 

rules that determine whether the randomly drawn 

points are inside or outside of the unknown volume, 

and the proportion of points that fall within these 

constraints multiplied by the volume of the known 

space is approximately equal to the unknown 

volume. In Monte Carlo integration, the estimate 

approaches the true value as the number of random 

points approaches infinity. 

We used R software (R Core Team 2012) to describe 

a box of known volume that was large enough 

to enclose the radar beam and then saturated 

this space with 10 million random points, and we 

determined two simple rules that defined whether 

a point was in the survey volume. The first rule was 

that the distance of the randomly drawn point from 

the origin had to be less than 2.8 km. The second 

rule was that the angle between a randomly drawn 

point and the vertical plane (the x-z axis in Figure 

7) had to be less than 12.5o (i.e., half the angle of 

the width of the beam). The volume of a full sweep 

of the radar beam, which was estimated by Monte 

Carlo integration, was within 5% of the analytical 

solution using spherical coordinates. Therefore, 

the number of random points we used provided 

a reasonable approximation of the volume. By 

determining the volume of a full sweep of the radar 

beam, we were able to further constrain the Monte 

Carlo integration to describe the structural volume 

of the radar beam within a standard front (Figure 7) 

and within altitude bands (Figure 8). 

12 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 13

Figure 7. A graphical representation of the structural volume of the vertical scanning radar within the 

standard front. In this graphic the radar unit is located at the origin, and the radar beam extends to 500 m 

on either side of the radar unit (x-axis) and up to a maximum height of 2800 m (z-axis). The y-axis represents 

the spread of the radar beam as it extends away from the origin. The orange semi-transparent points 

represent the volume contained by the structure of the radar beam. Dark gray points represent the volume 

that is within the box but is not included in the volume of the radar beam.

Figure 8. Volume of 50-m altitude bands within the standard front as estimated with Monte Carlo integration. Altitude band intervals represent the upper band limit. Target counts provided by the vertical scanning 

radar are limited to the structure of the standard front. The red line represents the top of the rotor swept 

zone at 130 m.

The number of targets per altitude band is often 

reported without providing a volume correction.

We wanted to compare our correction to the 

uncorrected method; however, count data and 

volume data are at different scales. For this reason, 

we compared our density estimate to a density 

estimate based on the number of targets per 

50-m altitude band per hour while assuming that 

there is an equal amount of volume within each 

altitude band (the volume of each altitude band is 

equal to the total volume divided by the number of 

altitude bands). An assumption implicit to reporting 

the number of targets per altitude band is that 

comparisons among bands can be made directly (i.e., 

that altitude bands are equal). For our comparison 

metric, we made this implicit assumption explicit 

(see Appendix 4).
14 Great Lakes Avian Radar - Fall 2012 

Results

Upper Peninsula of Michigan - Green Bay, Lake Michigan

During the fall 2012 season we began data collection 

at the West Delta County site on July 29 using the 

horizontal scanning radar. Due to water intrusion 

into the vertical scanning radar, which resulted in 

the radar’s malfunction and inability to collect data, 

we were not able to start collecting vertical scanning 

radar data until August 11. Water intrusion issues in 

the antenna also occurred with the radar unit that was 

placed at the Garden Peninsula site. Therefore, data 

collection from both vertical and horizontal radars 

started on August 9 at this site. Data collection ended 

at both sites on September 1, 2012. Our survey period 

at the West Delta County and Garden Peninsula sites 

captured migration activity; however, our survey 

period did not overlap with what is generally the peak 

of the fall migration season (generally September 

– October), so our results may not be indicative of 

what occurs during the height of migration. Data 

were recorded continuously while the radar units 

were operational, although gaps in the data collection 

occurred during rain events and when the radar 

units were not operational due to maintenance or 

malfunction (radar downtime). When correcting for 

radar downtime and removing the periods with rain, 

the vertical and horizontal radars collected usable data 

for 88% and 87% of the study period at the West Delta 

County site, and for 90% and 87% of the season at the 

Garden Peninsula site, respectively (Table 2).

Table 2. Survey effort (hours) by vertical and horizontal scanning radars during fall 2012 at our radar sites 

in West Delta County (WDC) and Garden Peninsula (GP). 

Site Radar

Survey 

Period

Radar 

Downtime

Time 

Radar 

Collected 

Data

Radar 

Data 

w/Rain

Useable 

Radar 

Data

% Survey 

Period 

with 

Collected 

Data

% Survey 

Period 

with 

Useable 

Data

WDC VSR1 570 52 518 15 503 91% 88%

WDC HSR 878 112 766 1 765 87 % 87%

GP VSR 562 37 525 17 508 93% 90%

GP HSR 562 72 490 1 488 87% 87%

1

Vertical and horizontal radars are not equally impacted by rain events or 

downtime.

Qualitative Assessments 

Plots of tracked targets showed images of nocturnal 

migration events at both locations (Figures 9 and 10). 

For example, on August 27 at the West Delta County 

site, the horizontal radar recorded scattered activity 

and the vertical radar recorded a low number of 

targets from 12:00 – 17:00 (Eastern Standard Time). 

During the 17:00 hour, a more directional movement 

of targets to the south and southwest began to occur, 

and vertical counts increased slightly. During the 20:00 

hour, directional movement to the south and southwest 

continued and targets began moving to the southeast 

as well; vertical counts increased at this time, with 

more targets at higher altitudes. A general southward 

movement continued throughout the night, with some 

western movement beginning around 01:00 on August 

28. As the night progressed, overall target counts 

tapered off, and target flight heights moved lower in 

altitude. At 06:00, some targets moved west off of the 

lake, and by 10:00 diurnal activity appeared similar to 

the proceeding day at 12:00 (Figure 9). This pattern of 

target movement and changes in flight altitude were 

indicative of a pulse of migratory activity.

A similar pattern of low target activity and flight 

heights during the day and increased directional 

activity and higher flight heights at night was also 

seen at the Garden Peninsula site (Figure 10). On 

August 26, targets moved southeast and east at 

20:00 and shifted to a mainly southeast direction by 

23:00. By 05:00 on August 27, the direction of target 

movement shifted again towards the south and west. 

This continued until after dawn, and by 11:00 target 

activity returned to non-directional diurnal movement. 

At the Garden Peninsula site, we also observed many 

1

Vertical and horizontal radars are not equally impacted by rain events or downtime.
Great Lakes Avian Radar - Fall 2012 15

Figure 9. Images of tracks during one hour increments recorded by horizontal and vertical scanning 

radars during a migration event at our West Delta County radar site. Horizontal radar images (columns 1 

and 3) show direction of targets as indicated by the color wheel (dark blue indicates travel to the north and 

red indicates travel to the south). Vertical radar images (columns 2 and 4) show target heights.
16 Great Lakes Avian Radar - Fall 2012 

Figure 10. Images of tracks during one hour increments recorded by horizontal and vertical scanning radars 

during a migration event at our Garden Peninsula radar site. Horizontal radar images (columns 1 and 3) 

show direction of targets as indicated by the color wheel (dark blue indicates travel to the north and red 

indicates travel to the south). Vertical radar images (columns 2 and 4) show target heights.
Photo Credit: B. Thompson

nights with reverse migration, with targets moving to 

the northeast. We attributed this to the early sampling 

dates that we had for this season. 

Also apparent on the Trackplots from both sites are 

areas not well recorded by the radar due to beam 

blockage from ground clutter (i.e., topography, 

vegetation, buildings, etc.) (Figure 4), thus resulting 

in reduced detection in the air space within the data 

collection range (e.g., south and west of the radar unit 

at the West Delta County site and north, east and 

west of the radar unit at the Garden Peninsula site, as 

observed in the horizontal Trackplots in Figures 9 and 

10). Rings of decreased detection near the radar unit 

and where the radar switched from short to medium 

pulse are also evident in both the horizontal (August 28, 

01:00) and vertical Trackplots (observed at a range of 

about 1,400 – 2,000 m).

Great Lakes Avian Radar - Fall 2012 17
18 Great Lakes Avian Radar - Fall 2012 

Directional Trends

During the fall 2012 season, the nocturnal target 

direction was generally south at West Delta County 

and southwest and southeast at the Garden Peninsula 

site (Figure 11). At our West Delta County site, the 

mean nocturnal direction was 152° (r = 0.17, n = 

2,681,116 targets) (Table 3) and during 52% of the 

nights the mean target direction was between the 

southeast and southwest (113.5° – 247.5°). Direction 

at the Garden Peninsula site had a mean nocturnal 

direction of 155° (r = 0.24, n = 1,634,581) with 62% 

of nights having a mean direction between southeast 

and southwest (Figure 11 and 12, Figure 3).

Figure 11. Target direction per hour during four biological periods during fall 2012 at our West Delta County (left) 

and Garden Peninsula (right) sites. Note different axis scales between the sites.

Table 3. Mean direction, angular concentration (r), and percentage of biological time periods with strong 

directionality (r ≥ 0.5) of targets during biological time periods at our West Delta County and 

Garden Peninsula sites. 

Target Direction per Hour during Four Biological Time Periods

West Delta County Garden Peninsula
Photo Credit: B. Thompson

Great Lakes Avian Radar - Fall 2012 19

Figure 12. Movement direction of targets for each night over the first part of the season. Each line represents the 

average movement direction targets were coming from for one night during the season. These directions assume that migrants move in a straight line, which is not the case, but it helps to show where the general direction 

of movement that migrants were coming from was located. These directions provide evidence that migrants fly 

along the Garden Peninsula and along the shoreline of Green Bay. The color of the lines indicates the magnitude of 

migration on that night. Count categories were derived using natural breaks (Jenks) classification. Date labels are 

missing for some lines that were too closely clumped together.

Temporal Trends

Time Series Plots. Hourly target counts provided 

by horizontal and vertical radars showed pulses of 

elevated nocturnal activity with nocturnal peaks 

occurring a few hours before and a few hours 

after midnight. Typically, we’ve seen this elevated 

nocturnal activity clustered into groups of several 

nights for many of our survey periods (see Figures 

13 and 14) (Bowden et al. 2015, Horton et al. 2016c, 

Rathbun et al. 2016, Rathbun et al. 2017). 

Elevated nocturnal activity occurred at the West 

Delta County and Garden Peninsula sites on August 

27 and continued through the last day of our survey 

period, September 1, with a lull in activity occurring 

on August 30 (Figures 13 and 14). Though at a lower 

magnitude, nocturnal activity occurred at these sites 

during the early parts of August as well.

Differences in detection capability of the vertical 

and horizontal scanning radars can be observed in 

Figures 13 and 14. For example, the horizontal radar 

at West Delta County shows an afternoon peak on 

August 20 at 13:00; however, this peak in activity 

is not represented by the counts obtained by the 

vertical scanning radar. This is possibly due to the 

flight path and lower altitudes of these targets. 
20 Great Lakes Avian Radar - Fall 2012 

Figure 13. Hourly counts by horizontal and vertical radars from July 29 – September 1, 2012, West Delta 

County. Due to water intrusion into the vertical scanning radar, resulting in the radar’s malfunction and 

inability to collect data, data collection from the vertical scanning radar began after repairs were made, on 

August 11. Light gray vertical lines represent midnight.

Figure 14. Hourly counts by horizontal and vertical radars from August 9 – September 1, 2012, Garden Peninsula. Light gray vertical lines represent midnight. 

Hourly Counts by Horizontal and Vertical Radars: West Delta County

Hourly Counts by Horizontal and Vertical Radars: Garden Peninsula
Great Lakes Avian Radar - Fall 2012 21

Target Passage Rate. The pattern of mean TPR 

among the four biological time periods was similar 

between the two study sites (Figure 15) with the 

mean TPR at night being greater than the combined 

means of the other three biological time periods 

(Table 4). The mean nocturnal TPR was 407 ± 

430 SD (n = 22 nights) and 392 ± 406 SD (n=23 

nights) at the West Delta County and Garden 

Peninsula sites, respectively. The mean TPR varied 

by hour with peak numbers reached during the 

21:00 and 22:00 hours at the West Delta County 

site and the 21:00 hour at the Garden Peninsula 

sight. An additional nighttime peak occurred after 

midnight at both sites and occurred at 01:00 at 

the West Delta County site and at 01:00 and 02:00 

at the Garden Peninsula site (Figure 16). At both 

locations, the mean TPR gradually decreased as 

the night progressed, with a more pronounced 

decline occurring between 05:00 and 06:00, which 

corresponds with the dawn time period.

Figure 15. Box plots showing variability in target passage rate (targets/km/hr) during four biological periods 

for fall 2012 in West Delta County and Garden Peninsula. Whiskers represent the 1st and 4th quartiles; 

boxes represent the 2nd and 3rd quartiles (with the line between indicating the median); the colored 

diamonds represent seasonal mean for the biological time period.

Table 4. Mean target passage rate (TPR) with standard deviations during four biological periods in West 

Delta County and Garden Peninsula during fall 2012.

Biological Period

West Delta 

County

Mean TPR

Garden 

Peninsula

Mean TPR

Dawn 100 ± 98 116 ± 117

Day 20 ± 17 32 ± 27

Dusk 44 ± 46 32 ± 21

Night 407 ± 430 392 ± 406
Weekly Mean of Target Passage Rates. Patterns 

of weekly means of nocturnal and diurnal target 

passage rates were similar at both sites (Figures 

17, 18 and 19). Weekly means of nocturnal TPR 

were consistently higher than weekly means of 

diurnal TPR. Nocturnal target passage rates were 

lower the first two weeks of the study period and 

increased during the third week of the study period, 

suggesting we left these sites just as migration was 

increasing. 

Figure 16. Mean hourly target passage rate (targets/km/hr) during fall 2012 at sites in West Delta County 

and Garden Peninsula.

Figure 17. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in West Delta County 

(top row) (August 11 – September 1, 2012) and Garden Peninsula (bottom row) (August 9 – September 1, 

2012). Error bars represent one standard deviation. Note different scales on nocturnal and diurnal plots.

22 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 23

Figure 18. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during fall 2012 at our West Delta County (top row) and Garden Peninsula (bottom row) radar sites. 
Figure 19. Comparison of nocturnal (top row) and diurnal (bottom row) target passage trends (based on a 

moving 7-day mean) during fall 2012 at our West Delta County and Garden Peninsula radar sites.

24 Great Lakes Avian Radar - Fall 2012 

Altitudinal Trends

Our density estimate that accounted for the 

geometric shape of the sampled space resulted 

in a substantially different density estimate than 

assuming an equal amount of sample volume 

per altitude band (Figures 20 and 21). Hourly 

altitude profiles at night revealed considerable 

variation in use of altitude bands (Figures 22 and 

23); however, over the course of the season, the 

200 – 250 m altitude band was the most densely 

used at both sites (Figure 24), with a total of 

3.26 targets/1,000,000 m3/night-hour and 3.22 

targets/1,000,000 m3/night-hour, respectively. The 

maximum density of targets was below 150 m during 

13.6% and 56.5% of the nights at the West Delta 

County and Garden Peninsula sites, respectively 

(Figure 25). A similar pattern occurred if the hours 

from 20:00 – 04:00 were considered individually, 

with the maximum density of targets occurring at 

less than 150 m during 17.0% and 55.4% of these 

night hours at the West Delta County and Garden 

Peninsula site, respectively (Figure 26).

At both sites, targets were observed within the 

entire range of altitude bands sampled. The mean 

altitude of nocturnal targets during the study 

period was 580 m ± 371 m SD and 526 m ± 370 m 

SD above the ground at our West Delta County 

and Garden Peninsula sites, respectively. Median 

altitude at night for the study period was 516 m 

and 459 m above ground at the West Delta County 

and Garden Peninsula sites, respectively. Mean and 

median altitudes were greatest during the dawn and 

night biological time periods (Table 5). The mean 

altitude per hour during the study period showed 
Great Lakes Avian Radar - Fall 2012 25

a similar pattern at both sites (Figure 27), where 

the mean altitude increased following dusk, peaked 

at 21:00, and generally decreased as the night 

progressed. An increase in mean altitude occurred 

near dawn at both sites.

Although many radar reports include estimates of 

the mean and median target altitudes, we found that 

these estimates were poor indicators of maximum 

density because of differences in the volume of air 

space sampled at various altitude bands. Figures 

28 and 29 are based on target density and show 

the variation in flight altitudes used by birds and 

bats that were counted by our vertical scanning 

radars throughout our survey period (August 11 – 

September 1, 2012 at the West Delta County site 

and August 9 – September 1, 2012 at the Garden 

Peninsula site). These graphics show the altitude 

bands of 0 – 1,300 m where most targets were 

counted (targets were counted up to 2,750 m, which 

is the extent of our sampling range). These graphics 

show that night hours at both sites had the highest 

density of flight activity and that the range of flight 

altitudes increased during the night hours. The 

graphics also show that many targets flew within, or 

just outside of a 30 – 130 m RSZ and that the mean 

and median altitudes do not reflect peak density 

altitudes, demonstrating how these values can 

misrepresent flight risk. 

Table 5. Comparison of mean altitude (m) with standard deviations, median altitude, and altitude band (50 m 

bands) that contained the maximum target density during four biological periods at our sites in West Delta 

County and Garden Peninsula during fall 2012. 

West Delta County Garden Peninsula

Biological 

Period Mean Median Max Band Density Mean Median Max Band Density

Dawn 632 ± 319 640 750 562 ± 338 515 300

Day 470 ± 387 400 200 341 ± 338 234 150

Dusk 400 ± 310 346 200 379 ± 351 297 150

Night 580 ± 371 516 200 526 ± 370 459 200
Figure 20. Altitude profile of targets at our site in West Delta County. Corrected lines depict target density 

(targets/1,000,000 m3) per 50-m altitude band per hour after adjusting for the structure of the sample 

volume. Uncorrected lines depict target density per 50-m altitude band per hour with an assumed uniform 

volume distribution (volume of each band is equal to the total volume divided by the number of bands). The 

red band represents the rotor swept zone (RSZ) between 30 – 130 m and the y-axis labels represent the top 

of the altitude band.

26 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 27

Figure 21. Altitude profile of targets at our site in Garden Peninsula. Corrected lines depict target density 

(targets/1,000,000 m3) per 50-m per hour altitude band after adjusting for the structure of the sample 

volume. Uncorrected lines depict target density per 50-m altitude band per hour with an assumed uniform 

volume distribution (volume of each band is equal to the total volume divided by the number of bands). 

The red band represents the rotor swept zone (RSZ) between 30 – 130 m and the y-axis labels represent 

the top of the altitude band.
Figure 22. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume at 

our site in West Delta County, during fall 2012. Hours were selected to portray the variability in density per 

altitude band of passing targets. The x-axis represents target density. The red line represents the top of the 

rotor swept zone at 130 m.

28 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 29

Figure 23. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume at 

our site in Garden Peninsula during fall 2012. Hours were selected to portray the variability in density per 

altitude band of passing targets. The x-axis represents target density. The red line represents the top of the 

rotor swept zone at 130 m.
Figure 24. Altitude profile of target density below 400 meters in West Delta County and Garden Peninsula. 

The x-axis represents target density (targets/1,000,000 m3) per 50-m altitude band. The y-axis represents 

altitude bands in meters.

Figure 25. Percent of nights when the maximum density (targets/1,000,000 m3/ altitude band) or count 

(targets/altitude band) occurred within 50-m altitude bands in West Delta County and Garden Peninsula, 

during fall 2012. 

30 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 31

Figure 26. Percent of night hours (20:00 – 04:00) when the maximum density (targets/1,000,000 m3/ altitude 

band) or count (targets/altitude band) occurred within 50-m altitude bands in West Delta County and 

Garden Peninsula, during fall 2012. 
Figure 27. Mean hourly target height (m) during fall 2012 at our West Delta County (top) and Garden 

Peninsula (bottom) sites. Orange and blue markers indicate the hours in which sunrise and sunset occurred 

during the season, respectively. Error bars represent one standard deviation.

32 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 33

Figure 28. Variation in flight altitudes based on target density (targets/1,000,000 m3) at our West Delta 

County site throughout the study period. Altitude bands are in meters, and labels represent the max value 

of each altitude band. Colors shown in each rectangle indicate the relative density observed for that altitude 

(key shown on the right) and time. The dark blue and light blue lines represent the nocturnal mean and 

median target heights, respectively. The black line at 130 m represents the max height of a turbine with a 

RSZ of 30 – 130 m. Note the difference in density scale used in other figures.
Figure 29. Variation in flight altitudes based on target density (targets/1,000,000 m3

) at our Garden 

Peninsula, Michigan site throughout the study period. Altitude bands are in meters, and labels represent the 

max value of each altitude band. Colors shown in each rectangle indicate the relative density observed for 

that altitude (key shown on the right) and time. The dark blue and light blue lines represent the nocturnal 

mean and median target heights, respectively. The black line at 130 m represents the max height of a 

turbine with a RSZ of 30 – 130 m. Note the difference in density scale used in other figures.

34 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 35

Table 6. Survey effort (hours) by vertical and horizontal scanning radars during fall 2012 at our Iosco 

County (IC) and West Huron County (WHC) radar sites. 

Lower Peninsula of Michigan – 

Saginaw Bay, Lake Huron

We began data collection September 2 and 6, 2012 

at the West Huron County and Iosco County sites, 

respectively. Data were recorded continuously while 

the radar units were operational, although gaps in 

the data collection occurred during rain events and 

when the radar units were not operational due

to maintenance or malfunction (radar downtime). 

When correcting for radar downtime and removing 

the periods with rain, the vertical and horizontal 

radars collected usable data for 89% and 99% of the 

study period at the Iosco County site, and for 88% 

and 99% of the season at the Garden Peninsula site, 

respectively (Table 6).

Qualitative Assessments

Plots of tracked targets showed images of nocturnal 

migration events at both locations (Figures 30 and 

31). For example, on October 26 at the Iosco County 

site the horizontal radar recorded scattered activity, 

and the vertical radar recorded a low number 

of targets from 12:00 – 15:00 (Eastern Standard 

Time). During the 17:00 hour, directional movement 

occurred with targets heading southward, and both 

horizontal and vertical target counts increased. 

Detection on both radars continued to increase 

as the night progressed, and the vertical radar 

detected more targets at higher altitudes around 

22:00. By 06:00, target counts decreased on both 

horizontal and vertical scanning radars, and 

westward movement towards shore occurred. 

By 12:00, diurnal activity appeared similar to the 

preceding day at 12:00 (Figure 30). This pattern 

of target movement and changes in altitude were 

indicative of a pulse of migratory activity. 

A similar pattern of low target activity and flight 

heights during the day and increased directional 

activity and higher flight heights at night was 

also seen at the West Huron County site. Figure 

31 shows targets moving southeast and south 

throughout the night. By 06:00, target movement 

shifted to the east, and the normal non-directional 

diurnal movement returned by 12:00.

Also apparent on the Trackplots from both sites are 

areas not well recorded by the radar due to beam 

blockage from ground clutter (due to topography, 

vegetation, buildings, etc.) (Figure 5), resulting 

in reduced detection in the air space that was 

within the range of data collection (e.g., north 

and northeast of the radar at Iosco County and 

in the center and southwestern areas of the West 

Huron County radar site, as seen in the horizontal 

Trackplots (Figures 30 and 31)). Rings of decreased 

detection near the radar unit and where the radar 

switched from short to medium pulse are also 

evident in both the vertical (October 26, 22:00 at 

Iosco County) and horizontal (October 21, 06:00 

at West Huron County) Trackplots (observed at a 

range of approximately 1,400 – 2,000 m).

Site Radar

Survey 

Period

Radar 

Downtime

Time 

Radar 

Collected 

Data

Radar 

Data 

w/Rain

Useable 

Radar 

Data

% Survey 

Period w/ 

Collected 

Data

% Survey 

Period w/

Useable 

Data

IC VSR1 1513 16 1497 150 1347 99% 89%

IC HSR 1513 11 1502 0 1502 99% 99%

WHC VSR 1609 23 1586 168 1418 99% 88%

WHC HSR 1609 19 1590 2 1588 99% 99% 1

Vertical and horizontal radars are not equally impacted by rain events or downtime.
Figure 30. Images of tracks during one hour increments recorded by horizontal and vertical scanning radars 

during a migration event at our radar site in Iosco County. Horizontal radar images (columns 1 and 3) show 

direction of targets as indicated by the color wheel (dark blue indicates travel to the north and red indicates 

travel to the south). Vertical radar images (columns 2 and 4) show target heights.

36 Great Lakes Avian Radar - Fall 2012 

 October 26, 12:00 October 26, 15:00
Great Lakes Avian Radar - Fall 2012 37

Figure 31. Images of tracks during one hour increments recorded by horizontal and vertical scanning radars 

during a migration event at our West Huron County radar site. Horizontal radar images (columns 1 and 3) 

show direction of targets as indicated by the color wheel (dark blue indicates travel to the north and red 

indicates travel to the south). Vertical radar images (columns 2 and 4) show target show target heights.

October 20, 11:00 October 20, 16:00
Figure 32. Target direction per hour during four biological periods during fall 2012 at our Iosco County (left) 

and West Huron County (right) radar sites. 

Table 7. Mean direction, angular concentration (r), and percentage of biological time periods with strong 

directionality (r ≥ 0.5) of targets during biological time periods at our Iosco County and West Huron County 

sites during fall 2012. 

38 Great Lakes Avian Radar - Fall 2012 

Directional Trends

During the fall 2012 season, nocturnal target 

direction was generally south/southwest at Iosco 

County and south/southeast at the West Huron 

County site (Table 7, Figure 32). At our Iosco 

County site, mean nocturnal direction was 191° 

(r = 0.48, n = 4,818,790 targets), and during 75% of 

nights mean target direction was between southeast

and southwest (113.5° – 247.5°). Direction at the 

West Huron County site had a mean nocturnal 

direction of 168° (r = 0.43, n = 4,232,783), with 60% 

of nights having a mean direction between southeast 

and southwest. Movement towards shore at dawn 

was observed at both sites (Figure 32). 

Iosco County West Huron County 

Biological 

Period

Mean 

Direction

(degrees) r

% Time 

r ≥ 0.5 n

Mean 

Direction

(degrees) r

% Time 

r ≥ 0.5 n

Dawn 217 0.34 36.5% 205,654 147 0.37 36.4% 272,882

Day 209 0.18 9.5% 903,062 218 0.03 1.5% 1,294,053

Dusk 187 0.21 20.6% 81,662 272 0.3 49.3% 117,913

Night 191 0.48 54.8% 4,818,790 168 0.43 65.2% 4,232,783

Target Direction per Hour during Four Biological Time Periods

 Iosco County West Huron County
Great Lakes Avian Radar - Fall 2012 39

Figure 33. Movement direction of targets for each night over the second part of the season. Each line 

represents the average movement direction targets were coming from for one night during the season. 

These directions assume that migrants move in a straight line, which was not the case, but it helped to show 

where the general direction of movement that migrants were coming from was located. The color of the 

lines indicates the magnitude of migration on that night. By focusing on the dark blue and pink lines (high 

migration nights), a pattern emerged at each site. In Iosco County, the migrants were mostly following the 

shoreline but had more than a few nights where they crossed over Saginaw Bay. In West Huron County, the 

majority of targets were arriving from across Saginaw Bay. These directions provide evidence that migrants 

are flying across the open water of the Great Lakes, as well as following along the shorelines. Count 

categories are derived using natural breaks (Jenks) classification. Date labels are missing for some lines 

that were too closely clumped together.

Temporal Trends

Time Series Plots – Hourly target counts provided 

by horizontal and vertical radars showed different 

activity patterns throughout the season, including 

pulses of elevated nocturnal activity. Across our 

sampling period, these pulses were often clustered 

into groups of several nights and were first observed 

on September 6 at both sites; September 6 was the 

first night of the survey period at Iosco County. 

Nocturnal peaks occurred a few hours before 

to a few hours after midnight. At both sites the 

occurrence and magnitude of nocturnal pulses 

decreased substantially by the end of October 

(Figures 34 and 35). 
Figure 34. Hourly counts by horizontal and vertical scanning radars from September 6 – November 7, 2012 

Iosco County, Michigan. Light gray vertical lines represent midnight.

40 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 41

Figure 35. Hourly counts by horizontal and vertical scanning radars from September 2 – November 7, 2012 

in Huron County, Michigan. Light gray vertical lines represent midnight.
42 Great Lakes Avian Radar - Fall 2012 

Target Passage Rate – The pattern of mean TPR 

among the four biological time periods was similar 

between the two study sites (Figure 36) with mean 

TPR at night being greater than the combined 

means of the other three biological time periods 

(Table 8). Mean nocturnal TPR was 664 ± 793 SD 

(n = 60 nights) and 344 ± 395 SD (n=62 nights) 

at the Iosco County and West Huron County sites, 

respectively. Mean TPR for the season varied by 

hour with peak numbers reached during the 22:00 

hour at Iosco County and at 20:00 at West Huron 

County. At both locations, mean TPR gradually 

decreased as the night progressed, with the most 

drastic decline occurring between 05:00 and 06:00 

(Figure 37).

Figure 36. Box plots showing variability in target passage rate (targets/km/hr) during four biological periods

for fall 2012 in Iosco and West Huron Counties. Whiskers represent the 1st and 4th quartiles;

boxes represent the 2nd and 3rd quartiles (with the line between indicating the median); the colored

diamonds represent seasonal mean for the biological time period.

Table 8. Mean target passage rate (TPR) with standard deviations during four biological periods at our 

Iosco County and West Huron County sites during fall 2012.
Great Lakes Avian Radar - Fall 2012 43

Figure 37. Mean hourly target passage rate during fall 2012 at our Iosco County and West Huron County 

radar sites. 

Weekly Mean of Target Passage Rates – The weekly 

means of nocturnal target passage rates were 

relatively high (compared to diurnal TPRs) at both 

sites, and both sites showed generally increasing 

means throughout the season, until late October, 

when the nocturnal mean TPRs began to decrease 

(Figure 38). The weekly means of nocturnal TPR 

were consistently higher than weekly means of 

diurnal TPR. As the recorded migration season 

subsided, there was less difference between the 

nocturnal and diurnal target passage rates (Figures 

39 and 40). Trends in both nocturnal and diurnal 

TPRs (7 day moving means) were similar at both 

sites.
44 Great Lakes Avian Radar - Fall 2012 

Figure 38. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) at our Iosco County 

(top row) and West Huron County (bottom row) radar sites during fall 2012. Error bars represent one 

standard deviation. Note different scales on nocturnal and diurnal plots.
Great Lakes Avian Radar - Fall 2012 45

Figure 39. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during fall 2012 at our Iosco County and West Huron County sites. 
46 Great Lakes Avian Radar - Fall 2012 

Figure 40. Comparison of nocturnal (top row) and diurnal (bottom row) target passage trends (based on a 

moving 7-day mean) during fall 2012 at our Iosco County (top row) and West Huron County sites (bottom 

row). 
Great Lakes Avian Radar - Fall 2012 47

Altitudinal Trends

Our density estimate that accounted for the 

geometric shape of the sampled space resulted 

in a substantially different density estimate than 

assuming an equal amount of sample volume 

per altitude band (Figures 41 and 42). Altitude 

profiles for all time periods differed between our 

two locations. Hourly altitude profiles at night 

revealed considerable variation in use of altitude 

bands (Figures 43 and 44); however over the 

course of the season, the 150 - 200 m altitude 

band and the 300 – 350 m altitude band were the 

most densely populated at the Iosco County and 

West Huron County sites (Figure 45), with a total 

of 6.03 targets/1,000,000 m3/night-hour and 3.08 

targets/1,000,000 m3/night-hour, respectively. The 

maximum density of targets was below 150 m during 

57.8% and 36.4% of the nights at the Iosco County 

and West Huron County sites, respectively (Figure 

46). A similar pattern occurred when considering 

nocturnal hours individually with the maximum 

density of targets being below 150 m during 50.3% 

and 33.4% of night hours (Figure 47).

At both sites, targets were observed within the 

entire range of altitude bands sampled. Mean 

altitude of nocturnal targets was 522 m ± 327 m 

SD and 505 m ± 296 m SD above radar elevation 

at the Iosco County and West Huron County sites, 

respectively (Table 9). The median altitude at night 

was 466 m and 460 m above radar elevation at the 

Iosco and West Huron County sites, respectively. 

The median altitude was greatest during the night 

and dawn biological time periods. The mean altitude 

per hour during the season showed a similar pattern 

at the two locations (Figure 48). The mean altitude 

increased around dusk and tapered an hour or two 

afterwards. The mean target heights gradually 

decreased throughout the night, with a spike in 

mean altitude occurring around dawn.

Although many radar reports include estimates of 

the mean and median target altitudes, we found that 

these estimates were poor indicators of maximum 

density because of differences in the volume of air 

space sampled at various altitude bands. Figures 

49 and 50 are based on target density and show 

the variation in flight altitudes used by targets 

that were counted by our vertical scanning radars 

throughout our survey period (Sept 6 – November 

7, 2012 at the Iosco County site and September 

2 – November 7, 2012 at the West Huron County 

site). These graphics show the altitude bands of 0 – 

1,300 m where most targets were counted (targets 

were counted up to 2,750 m, which is the extent 

of our sampling range). These graphics show that 

night hours at both sites had the highest density of 

flight activity and that the range of flight altitudes 

increased during the night hours. The graphics also 

show that many targets flew within, or just outside 

of a 30 – 130 m RSZ, and that the mean and median 

altitudes do not reflect peak density altitudes, 

demonstrating how these values can misrepresent 

flight risk. 

Table 9. Comparison of mean altitude (m) with standard deviations, median altitude, and altitude band (50 

m bands) that contained the maximum target density during four biological periods at our sites in Michigan 

during fall 2012. 

Iosco County West Huron County

Biological 

Period Mean Median Max Band Density Mean Median Max Band Density

Dawn 500 ± 366 432 100 471 ± 337 405 100

Day 386 ± 278 345 100 319 ± 314 210 100

Dusk 483 ± 338 388 100 309 ± 343 200 150

Night 522 ± 327 466 200 505 ± 296 460 350
48 Great Lakes Avian Radar - Fall 2012 

Figure 41. Altitude profile of targets at our Iosco County site. Corrected lines depict target density 

(targets/1,000,000 m3) per 50-m altitude band per hour after adjusting for the structure of the sample 

volume. Uncorrected lines depict target density per 50-m altitude band per hour with an assumed uniform 

volume distribution (volume of each band is equal to the total volume divided by the number of bands). The 

red band represents the rotor swept zone (RSZ) between 30 – 130 m, and the y-axis labels represent the top 

of the altitude band.
Great Lakes Avian Radar - Fall 2012 49

Figure 42. Altitude profile of targets at our West Huron County site. Corrected lines depict target density 

(targets/1,000,000 m3) per 50-m per hour altitude band after adjusting for the structure of the sample 

volume. Uncorrected lines depict target density per 50-m altitude band per hour with an assumed uniform 

volume distribution (volume of each band is equal to the total volume divided by the number of bands). The 

red band represents the rotor swept zone (RSZ) between 30 – 130 m, and the y-axis labels represent the top 

of the altitude band.
50 Great Lakes Avian Radar - Fall 2012 

Figure 43. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume 

at our site in Iosco County, during fall 2012. Hours were selected to portray the variability in density per 

altitude band of passing targets. The x-axis represents target density (targets/1,000,000 m3) per 50-m 

altitude band. The y-axis represents altitude bands in meters. The red line represents the top of the rotor 

swept zone at 130 m.
Great Lakes Avian Radar - Fall 2012 51

Figure 44. A sample of hourly nocturnal altitude profiles corrected for the shape of the sample volume

at our West Huron County site during fall 2012. Hours were selected to portray the variability in density 

per altitude band of passing targets. The x-axis represents target density (targets/1,000,000 m3) per 50-m 

altitude band. The y-axis represents altitude bands in meters. The red line represents the top of the rotor 

swept zone at 130 m.
52 Great Lakes Avian Radar - Fall 2012 

Figure 45. Altitude profile of target density below 400 meters in at our sites in Iosco County and West Huron 

County during fall 2012. The x-axis represents target density (targets/1,000,000 m3) per 50-m altitude band. 
Great Lakes Avian Radar - Fall 2012 53

Figure 46. Percent of nights when the maximum density (targets/1,000,000 m3/ altitude band) or count

(targets/altitude band) occurred within 50-m altitude bands at our Iosco County and

West Huron County study sites, during fall 2012. 
Figure 47. These graphics show the percent of night hours (20:00 – 04:00) when the maximum density

(targets/1,000,000 m3/ altitude band) or count (targets/altitude band) occurred within 50-m altitude bands

our Iosco County and West Huron County study sites, during fall 2012.

54 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 55

Figure 48. Mean hourly target height (m) during fall 2012 at our Iosco County (top) and West Huron County 

(bottom) sites. Orange and blue markers indicate the hours in which sunrise and sunset occurred during the 

season, respectively. Error bars represent one standard deviation.
56 Great Lakes Avian Radar - Fall 2012 

Figure 49. Variation in flight altitudes based on target density (targets per million cubic m) at our Iosco 

County, Michigan site throughout the fall 2012 study period. Altitude bands are in meters, and labels 

represent the max value of each altitude band. Colors shown in each rectangle indicate the relative density 

observed for that altitude (key shown on the right) and time. The dark blue and light blue lines represent 

the nocturnal mean and median target heights, respectively. The black line at 130 m represents the max 

height of a turbine with a RSZ of 30 – 130 m. Note the difference in density scale used in other figures. 
Figure 50. Variation in flight altitudes based on target density (targets per million cubic m) at our West 

Huron County, Michigan site throughout the fall 2012 study period. Altitude bands are in meters, and labels 

represent the max value of each altitude band. Colors shown in each rectangle indicate the relative density 

observed for that altitude (key shown on the right) and time. The dark blue and light blue lines represent 

the nocturnal mean and median target heights, respectively. The black line at 130 m represents the max 

height of a turbine with a RSZ of 30 – 130 m. Note the difference in density scales used in other figures. 

Great Lakes Avian Radar - Fall 2012 57
58 Great Lakes Avian Radar - Fall 2012 

Discussion

We undertook this study to document migration 

along the shorelines of the Great Lakes. We found 

that migration movements were common along the 

shorelines of northern Lake Michigan and western 

Lake Huron (where we established our study sites), 

and we believe that the data collected at these four 

sites are generally representative of migration along 

these shorelines, even if our time on northern Lake 

Michigan was for a short part of the season. Our 

research contributes to a growing body of literature 

that documents various aspects of migration and 

identifies the Great Lakes shorelines as areas 

important for conservation of migratory species. Our 

data provide unique observations about the magnitude 

and timing of nocturnal migration that could not be 

observed without the aid of radar technology.

Additionally, the gathered data may be useful outside 

of its application to wind energy development.

Areas viewed as concentration areas may be higher 

prioritized for habitat conservation or enhancement. 

While specific habitat patches may be hard to evaluate 

using marine radar data, general trends of where 

migrants are traveling to can be found and further 

investigated with on the ground surveys. 

Sampling Regime 

Sampling regime is an important consideration for 

migration studies. Migratory movements are guided, in 

part, by environmental conditions and occur in pulses 

across the migratory season (Alerstam 1990). Our 

continuous sampling scheme captured the timing of 

migration events and provided a more complete picture 

of the migratory season than a systematic or random 

sampling scheme, which may have missed pulses of 

activity (Figure 51). Even with splitting the season 

and our short amount of time in the Upper Peninsula, 

we were able to see patterns in migration using our 

continuous sampling scheme. We used diurnal radar 

observations to provide a baseline for comparing 

nocturnal activity, and including this time period 

helped to distinguish the magnitude of migration 

events (Figures 15 and 36). Our sampling regime was 

also useful in showing when the migration season for 

passerines and bats declined in late October. Although 

by moving from the Upper Peninsula sites to the 

Lower Peninsula sites in early September, we missed 

documenting the full migration for each site. As more 

data are collected, we will be able to better describe the 

migration season and how it varies with location and 

year. This information will help conservation efforts to 

be tailored to appropriate time frames. 

Site Comparison Considerations

Target counts provided by radar are influenced by 

radar type and calibration, filtering of non-intended 

targets, count algorithms, frequency band, antenna 

orientation, sampling scheme, and how researchers 

account for variation in detection probability and 

sample volume (Bruderer 1997, Harmata et al. 1999, 

Schmaljohann et al. 2008). Even when the same 

equipment and methodology are used among sites 

or studies, comparisons should be made cautiously 

if the probability of detection and sampling volume 

are ignored (Schmaljohan et al. 2008). Recognizing 

that our counts represent an index of target passage 

that is relative to a site, we are cautious in making 

comparisons among sites or studies. Rather than 

relying solely on the magnitude of the target passage 

as an indication of migration, we assess the patterns of 

activity among sites to compare the relative strength of 

migration. For example, a site with a nocturnal passage 

rate that shows peaks that are many times larger than 

nocturnal lulls for the majority of the sampling period 

would likely be considered to have more migration than 

a site with less of a discrepancy between nocturnal 

peaks and lulls or a site that had a nocturnal passage 

rate that only occasionally spiked above a baseline of 

nocturnal passage rates. 
Great Lakes Avian Radar - Fall 2012 59

Figure 51. Example of a hypothetical sampling schedule where data were collected once per week (top 

graphic) versus the actual continuous sampling schedule (bottom graphic). Red lines represent the number 

of targets counted per hour by the vertical scanning radar from September 6 – October 5, 2012 at our Iosco 

County site.

Migration Patterns

The patterns of movement we recorded were 

consistent with other observations of migration 

(Newton 2008) and they indicated that nocturnal 

migratory flights occurred regularly in fall 2012 

at our surveyed locations. The nocturnal activity 

we observed was typically oriented in a southerly 

direction (Figures 11-12 and 32-33) and occurred 

in pulses across the season that were captured by 

horizontal and vertical radars (Figures 13, 14, 34, 

and 35). During the night, targets often traveled 

perpendicular to the shorelines, heading out over 

the water to cross to the other side, while at dawn 

we observed targets that were flying over water 

return to shorelines. Movement towards shore at 

dawn may be due to migrants drifting with the wind 

as they migrate and needing to adjust their position 

at dawn to find suitable stopover habitat to rest and 

refuel (Horton et al. 2016b). While these patterns 

were common, they were not observed every night. 

Occasionally we observed migration in the opposite 

direction, indicating that reverse migration occurred 

at all sites, although this was more common earlier 

in the season. Target passage rate (mean for the 

season) was greatest during the nocturnal biological 

time period at all locations (Tables 4 and 8, Figures 

15 and 36). Mean hourly heights showed a pattern 

previously associated with migration (Harmata et 

al. 2000, Mabee and Cooper 2004) with heights that 

increased near dusk, peaked at night, and began 

to decrease prior to dawn. The slight increase in 

mean height near dawn at our sites (Figure 27 

and 48) is consistent with a migratory behavior 

described as dawn ascent (Myres 1964, Diehl et 

al. 2003). This behavior is attributed to migrants 

increasing altitude to gain a broader view of the 

surrounding landscape before selecting stopover 

habitat or returning to the shoreline if they were 

flying over water. Taken together, we attribute these 

nocturnal observations to migrants and suggest that 

the shorelines we studied are important for their 

conservation.
60 Great Lakes Avian Radar - Fall 2012 

While comparing direct numbers between sites 

is problematic, overall trends can be more easily 

compared. In general, we observed similar 

behaviors at similar times when looking at different 

sites. Nocturnal migration started at generally the 

same time and often moved in generally the same 

direction when comparing West Delta County with 

Garden Peninsula or Iosco County with West Huron 

County. General magnitude was also similar between 

sites on a given night, and there were rarely times 

when one of the sites had large numbers and the 

other site did not. These pattern comparisons 

provide evidence for broad scale movements of 

migrants across the landscape and that these 

movements may be due to broad scale influences 

such as weather front movements.

At our four sample locations, nocturnal targets 

appeared to move across the landscape in waves 

with peaks starting on August 27 at both of our 

sites located near Lake Michigan (Figures 13 and 

14). Due to our longer sampling period at our Iosco 

and West Huron County sites, located near Lake 

Huron, we were able to capture a series of peaks 

that occurred beginning in early September and 

extending through late October (Figures 34 and 

35). These fluctuations may be related to broad 

scale weather fronts, variation in timing among 

guilds of migrants, or a combination of these and 

other factors (Newton 2008). The pattern of these 

trends at our study locations suggests broadscale influences and could indicate that further 

investigation into their cause would allow prediction 

of high migration events. 

The weekly mean nocturnal TPR estimates were 

consistently higher than weekly mean diurnal TPR 

estimates throughout the data collection period 

(Figures 18 and 39), with peaks between late 

August and late October. The difference between 

peaks was diminished in early August, late October, 

and early November. This shift from time periods 

with significantly higher nocturnal activity to time 

periods with diminished nocturnal activity indicates 

that migration substantially contributed to the 

aeroecology above our study areas.

Flight Altitude

Altitude profiles indicated that most nocturnal 

targets passed below 800 m, with peak density 

between the 100 and 350 m altitude bands 

(Figures 20, 21, 24, 41, 42 and 45). We corrected 

for the approximate shape of the survey volume 

and included this correction in our density 

estimates, although this correction is based on 

the manufacturer’s estimate of beam geometry, 

which may not be precise. Furthermore, beam 

propagation was not consistent over time because it 

was affected by side lobes, target size and distance, 

and atmospheric conditions. Nevertheless, we 

believe that the correction was an improvement 

over the altitude profiles that ignored beam 

geometry and sampling effort. We were not able 

to correct for the loss of detection with distance 

from the radar (Schmaljohann et al. 2008), and our 

vertical scanning radars lost detection at a range 

of approximately 1,400 – 2,000 m, which was where 

the radar transitioned from the short to medium 

pulse. For these reasons, our estimates likely 

under-represented the density as altitude increases. 

However, the densities per altitude band were 

already decreasing (Figure 20-21 and 41-42) before 

the 1,400 m band, and any undercount would be 

unlikely to change the overall picture.

The reported altitude profiles varied considerably 

among nocturnal hours at our four study sites 

(Figures 22, 23, 43 and 44). Migrants likely adjusted 

flight altitude with wind direction and speed, 

visibility, time, and landscape below flight trajectory 

(Alerstam 1990, Hueppop et al. 2006, Liechti 2006). 

For example, head winds aloft have resulted in 

migrants moving en masse to lower altitudes that 

present lower wind speeds (Gauthreaux 1991). In 

addition, migrants are typically on land at least 

twice during every 24-hour period. Changes in flight 

altitude can occur at various times over the course of 

the night and are associated with targets ascending 

from and descending to stopover sites. Depending 

on location, these altitude changes may place 

migrants at risk of collision with wind turbines. 

Radar Study Considerations

Although radar may be the best tool available 

for gathering large amounts of data on nocturnal 

migration, the interpretation of radar data can be 

challenging. Marine radar is the most common type 

of radar used to track the movements of birds and 

bats (Larkin 2005), and its use in risk assessments 

will likely increase with the expected increase in 

wind energy development. Despite this growing 

trend, standardized equipment and methodologies 

for establishing radar settings, ground-truthing 

biological targets, and data processing have not 

been adopted, although such considerations would 

substantially improve the quality of the data and 

the conclusions drawn from them. Standardization 

presents an enormous challenge; however, without 

it, comparisons among studies may be more 

reflective of changes in equipment, methodology, and 

site conditions rather than differences in migratory 

activity among sites. 

Additionally, the metrics reported in radar surveys 

can be misleading to anyone unfamiliar with avian 

radar. For example, the mean altitude of target 

passage is often reported to be above the rotorswept zone and has been interpreted to indicate low 
Great Lakes Avian Radar - Fall 2012 61

risk. However, the mean altitude can be well above 

the rotor-swept zone, even when there is a high rate 

of target passage within the zone because of the long 

range over which radars collect altitude data, which 

was up to 3 km above the ground in our study; thus, 

high flying targets can inflate the mean altitude. This 

bias was apparent in our data and can be observed 

by comparing the mean altitude of nocturnal targets 

to the most densely populated altitude band (Figures 

24-26, 28-29, 45-47, 49-50, and Tables 5 and 9). It is 

also misleading to compare the percent of targets 

below and above the height of the rotor-swept zone 

without addressing the inherent difference in radar 

sampling effort at various altitude bands. Within 

our sampling framework, there were three 50-m 

altitude bands below 150 m (an estimate for the 

height of the rotor-swept zone) and 53 altitude bands 

above 150 m. Based on our model, we estimated that 

approximately 1% of the potential survey volume 

was below 150 m. Therefore, we would expect a 

small percentage of targets to be recorded at or 

below the rotor-swept zone, although this does not 

necessarily indicate low risk. Additionally, sampling 

in areas in the lower altitude bands is often poor due 

to the effects of ground clutter (Figure 4 and 5).

When examining general migration patterns, high 

nighttime migrant activity was documented at our 

Lake Michigan and Lake Huron radar sites as 

demonstrated by our Trackplots (Figures 9, 10, 30, 

31), the time series plots from each site (Figures 

13, 14, 34, and 35), and high target passage rates 

(Figures 15, 16, 36, and 37 and Tables 4 and 8). 

Percent of targets within a 30 – 130 m rotor-swept 

zone were high during all biological time periods, 

with target density being highest at night (Figures 

15-21 and 36-42). Throughout the migration season, 

nighttime targets were recorded flying along the 

shorelines and across the lake (Figures 9, 10, 12, 30, 

31 and 33). As dawn approaches nighttime migrants 

need a place for refuge, rest, and foraging, thus 

migrants flying over water have been recorded 

returning towards shore around dawn. The 

combination of these behaviors indicates that high 

numbers of nighttime migrants may be at risk of 

collision with wind facilities, communication towers, 

or other tall structures located along the shorelines 

of Lakes Michigan and Huron. 

Although the target passage rate and target 

density were lower during the dawn, day, and dusk 

periods, the migrants may still be at risk of collision 

during these time periods. Targets were recorded 

flying along the lakeshore, indicating that the 

Lakes Michigan and Huron shorelines are used by 

migrants during all times of the day in the migration 

season for both migratory flightpaths and stopover 

habitat. 

Conclusions

In this report we provide examples of methodology 

and analyses that we find helpful in interpreting 

radar data. We suggest the relative change in counts 

at a site indicate the level of migration activity, 

and this is a better indicator than comparing the 

magnitude of counts among studies. As well, careful 

attention should be given to how these indices 

fluctuate over fine temporal scales, such as hourly, 

as opposed to monthly or seasonal summaries. The 

clutter maps we include provided information about 

our ability to detect targets at various altitudes, 

and we think it is important, particularly for risk 

assessment, that radar operators address their 

ability to detect targets at low altitude. We provided 

a method to account for the structure of the sample 

volume that, while not without limitations, provided 

a partial solution rather than ignoring the biases 

associated with sampling effort. Overall, we found 

that radar provided insight into nocturnal migration 

that would otherwise be unattainable, and we 

think that its continued development and careful 

interpretation will result in valuable contributions to 

the management and conservation of migrants.

The results of our research highlight the potential 

role of radar in implementing recommendations 

from the Land-based Wind Energy Guidelines 

(USFWS 2012) for the identification of areas 

where impacts to wildlife should be minimized. We 

documented examples of migrant activity along 

the northern shorelines of Lake Michigan and the 

western shorelines of Lake Huron at our study sites, 

and the density of targets at lower altitudes is a 

potential concern. Additionally, increases in turbine 

heights and blade lengths increase the size of the 

rotor-swept zone, thus creating larger areas of flight 

risk for birds and bats. The collected data may be 

of interest to public and private entities involved 

with wind energy development and the potential 

placement of turbines in the Great Lakes region as 

well as decision makers evaluating land conservation 

and stopover habitat use. Coupling avian radar 

systems with other forms of research or using 

radar in conjunction with post-construction fatality 

searches may broaden the utility of their use in risk 

assessments of wind energy developments. 
62 Great Lakes Avian Radar - Fall 2012 

Literature Cited

Able, K. P. 1977. The flight behaviour of individual 

passerine nocturnal migrants: a tracking radar 

study. Animal Behaviour 25:924–935.

Akesson, S. 1999. Do passerine migrants captured at 

an inland site perform temporary reverse 

migration in autumn? Ardea 87:129-138.

Alerstam, T. 1990. Bird Migration. Cambridge 

University Press, Cambridge.

Alerstam, T. 2001. Detours in bird migration. Journal 

of Theoretical Biology 209:319-331.

Arnett, E. B., and E. F. Baerwald. 2013. Impacts of 

wind energy development on bats: Implications 

for conservation. Pages 435–456 in R. A. Adams 

and S. C. Pederson. Editors. Bat Ecology, 

Evolution and Conservation. Faller Science 

Press, New York, USA.

Arnett, E. B., W. K. Brown, W. P. Erickson, 

J. K. Fiedler, B. L. Hamilton, T. H. Henry, 

A. Jain, G. D. Johnson, J. Kerns, R. R. Koford, 

C. P. Nicholson, T. J. O’Connell, M. D. 

Piorkowski, and R. D. Tankersley, Jr. 2008. 

Patterns of bat fatalities at wind energy 

facilities in North America. Journal of Wildlife 

Management 72:61-78.

Audubon. 2013. Important Bird Areas Program. 

http://web4.audubon.org/bird/iba/. Last 

accessed August 2013.

AWEA. 2015. American Wind Energy 

Association. http://www.awea.org/Issues/

Content.aspx?ItemNumber=4437. 

Last accessed January 2015.

BHE Environmental, Inc. 2010. Post-construction

bird and bat mortality study Cedar Ridge wind 

farm Fond Du Lac County, Wisconsin.

Unpublished interim report.

www.bheenvironmental.com

Bingman, V. P. 1980. Inland morning flight behavior 

of nocturnal passerine migrants in eastern 

New York. Auk 97: 465-472.

Bonter, D., T. Donovan, and E. Brooks. 2007. Daily 

mass changes in landbirds during migration 

stopover on the south shore of Lake Ontario.

Auk 124:122–133.

Bonter, D., S. A. Gauthreaux, Jr., and T. M. Donovan. 

2009. Characteristics of important stopover 

locations for migrating birds: remote sensing 

with radar in the Great Lakes Basin.

Conservation Biology 23:440-448.

Bowden, T. S., E. C. Olson, N. A. Rathbun, D. C. Nolfi, 

R. L. Horton, D. J. Larson, and J. C. Gosse. 

2015. Great Lakes Avian Radar Technical 

Report Huron and Oceana Counties, Michigan.

U.S. Department of Interior, Fish and Wildlife 

Service, Biological Technical Publication 

FWS/BTP-R3011-2015 

Bowlin, M.S., D.A. Enstrom, B.J. Murphy, E. Plaza, 

P. Jurich, and J. Cochran. 2015. Unexplained 

altitude changes in a migrating thrush: 

Long-flight altitude data from radio-telemetry.

The Auk: Ornithological Advances 132: 808-816.

Bruderer, B. 1997. The study of bird migration by 

radar, Part 1: The technical basis.

Naturwissenschaften 84: 1-8.

Bruderer, B., and F. Liechti. 1998. Flight behaviour 

of nocturnally migrating birds in coastal areas - 

crossing or coasting. Journal of Avian Biology 

29:499-507.

Buler, J. J. and F. Moore. 2011. Migrant-habitat 

relationships during stopover along an 

ecological barrier: extrinsic constraints and 

conservation implications. Journal of 

Ornithology 152:101-112.

Buler, J. J. and D. K. Dawson. 2012. Radar analysis 

of fall bird migration stopover sites in the 

Northeast U.S. Final Report. Cooperative 

Agreement USGS and University of Delaware.

Cryan, P.M. 2011. Wind turbines as landscape 

impediments to the migratory connectivity of 

bats. Environ Law. 41:355-370.

DeTect, Inc. 2009. MERLIN avian radar survey for a 

proposed wind project. Unpublished technical 

report. Panama City, FL.

Diehl, R. H., R. P. Larkin, and J. E. Black. 2003. Radar

 observations of bird migration over the Great 

Lakes. Auk 120:278-290.

Diehl, R. H., J. E. Bates, D. E. Willard, and 

T. P. Gnoske. 2014. The hazards of nocturnal 

migration over Lake Michigan: a case study.

Wilson Journal of Ornithology. 126:19-29.

Ewert, D.N., P.J. Doran, K.R. Hall, A. Froelich, 

J. Cannon, J.B. Cole, and K.E. France. 2012. 

On a wing and a (GIS) layer: Prioritizing 

migratory bird stopover habitat along Great

Lakes Shorelines. Final report to the Upper 

Midwest/Great Lakes Landscape Conservation 

Cooperative.
Great Lakes Avian Radar - Fall 2012 63

Ewert, D. N., M. J. Hamas, R. J. Smith, 

M. E. Dallman, and S. W. Jorgensen. 2011. 

Distribution of migratory landbirds along the 

northern Lake Huron shoreline. Wilson Journal

of Ornithology 123:536-547.

Faaborg, J., R. T. Holmes, A. D. Anders, 

K. L. Bildstein, K. M. Dugger, 

S. A. Gauthreaux, Jr., P. Heglund, K. A. Hobson, 

A. E. Jahn, D. H. Johnson, S. C. Latta, 

D. J. Levey, P. P. Marra, C. L. Merkord, 

E. Nol, S. I. Rothstein, T. W. Sherry, 

T. S. Sillett, F. R. Thompson, III, and 

N. Warnock. 2010. Conserving migratory 

land birds in the New World: Do we know 

enough? Ecological Applications 20:398-418.

France, K. E., M. Burger, T. G. Howard, 

M. D. Schlesinger, K. A. Perkins, M. MacNeil, 

D. Klein, and D. N. Ewert. 2012. Final 

report for Lake Ontario Migratory Bird 

Stopover Project. Prepared by The Nature 

Conservancy for the New York State 

Department of Environmental Conservation, 

in fulfillment of a grant from the New York 

Great Lakes Protection Fund (C303907).

Gauthreaux, S. A. 1991. The flight behavior of 

migrating birds in changing wind fields – radar 

and visual analyses. American Zoologist 

31:187-204.

Gerringer, M.B., S.L. Lima, T. L. DeVault. 2015. 

Evaluation of an avian radar system in a 

Midwestern landscape. Wildlife Society 

Bulletin 1-10.

Great Lakes Commission. 2011. State of the science: 

an assessment of research on the ecological 

impacts of wind energy in the Great 

Lakes Region. Report by the Great Lakes 

Wind Collaborative, Great Lakes 

Commission, 19 p.

Grodsky, S. M., C.S. Jennelle, D. Drake, and 

T. Virizi. 2012. Bat mortality at a wind-energy 

facility in southeastern Wisconsin. Wildlife 

Society Bulletin 36(4):773-783.

Gruver, J., M. Sonnenburg, K. Bay, and W. Erickson. 

2009. Post-construction bat and bird fatality 

study at the Blue Sky Green Field Wind 

Energy Center, Fond Du Lac County, 

Wisconsin. Western EcoSystems Technology, 

Inc. Unpublished final report. 

Harmata, A. R., K. M. Podruzny, J. R. Zelenak, 

and M. L. Morrison. 1999. Using marine 

surveillance radar to study bird movements 

and impact assessment. Wildlife Society 

Bulletin 27:44-52.

Harmata, A. R., K. M. Podruzny, J. R. Zelenak, and 

M. L. Morrison. 2000. Passage rates and timing 

of bird migration in Montana. American 

Midland Naturalist 143:30-40.

Hayes, M. 2013. Bats killed in large numbers at 

United States Wind Energy Facilities.

Bioscience 63: 975-979.

Horton, K.G., W.G. Shriver, and J.J. Buler. 2015. 

A comparison of traffic estimates of nocturnal 

 flying animals usingradar, thermal imaging, and 

acoustic recording. Ecological Applications 

25(2): 390-401.

Horton, K.G., W.G. Shriver, and J.J. Buler. 2016a. 

An assessment of spatio-temporal relationships 

between nocturnal bird migration traffic rates 

and diurnal bird stopover density. Movement 

Ecology 4: 1.

Horton, K.G., B.M. Van Doren, P.M. Stepanian, 

W.M. Hochachka, A. Farnsworth, and J.F. Kelly. 

2016b. Nocturnally migrating songbirds drift 

when they can and compensate when they must.

Scientific Reports 6: 1-8.

Horton, R.L., N.A. Rathbun, T. S., Bowden, 

D. C. Nolfi, E. C. Olson, D. J. Larson, and

 J. C. Gosse. 2016c. Great Lakes Avian Radar 

Technical Report Lake Erie Shoreline: Erie 

County, Ohio and Erie County, Pennsylvania.

Spring 2012. U.S. Department of Interior, 

Fish and Wildlife Service, Biological Technical 

Publication FWS/BTP-R3013-2016 

Hueppop, O., J. Dierschke, K. M. Exo, E. Fredrich, 

and R. Hill. 2006. Bird migration studies and 

potential collision risk with offshore wind 

turbines. Ibis 148:90-109.

Huron County. 2015. http://www.co.huron.mi.us/about_

overview.asp. Last accessed February 2015.

Jin, S., Yang, L., Danielson, P., Homer, C., 

Fry, J., and Xian, G. 2013. A comprehensive 

change detection method for updating the 

National Land Cover Database to circa 2011.

Remote Sensing of Environment, 132: 159 – 175.

Johnson, G.D. 2005. A review of bat mortality at 

wind-energy developments in the United States.

Bat Research News. 46: 45-49. 

Johnson, P. L. 2013. Migratory Stopover of Songbirds 

in the Western Lake Erie Basin (Doctoral 

dissertation, The West Delta County State 

University).

Kunz, T. H., E. B. Arnett, W. P. Erickson, A. Hoar, 

G. Johnson, R. Larkin, M.D. Strickland, 

R. Thresher, and M. Tuttle. 2007a. Ecological 

impacts of wind energy development on bats: 

questions, research needs, and hypotheses.

Frontiers of Ecology and the Environment

 5(6):315-324.

Kunz, T. H., E. B. Arnett, B. M. Cooper, 

W. P. Erickson, R. P. Larkin, T. Mabee, 

M. L. Morrison, M. D. Strickland, and 

J. M. Szewczak. 2007b. Assessing impacts of 

wind-energy development on nocturnally 

active birds and bats: a guidance document.

Journal of Wildlife Management 71:2449–2486.
64 Great Lakes Avian Radar - Fall 2012 

Larkin, R.P. 2005. Radar techniques for wildlife 

biology. Pages 448-464 In: C. E. Braun, 

editor Techniques for wildlife investigations 

and management, 6th Edition. The Wildlife 

Society, Bethesda, Maryland, USA.

Liechti, F., B. Bruderer, and H. Paproth. 1995. 

Quantification of nocturnal bird migration by 

moonwatching: comparison with radar and 

infrared observations. J. Field Ornithol. 

66: 457–468.

Liechti, F. 2006. Birds: blowin’ by the wind? Journal 

of Ornithology 147:202-211.

Loss, S., T. Will, and P. Marra. 2013. Estimates of 

bird collision mortality at wind facilities in the 

contiguous United States. Biological 

Conservation, 168:201-209.

Lowery, G.H. Jr. 1951. A quantitative study of the 

nocturnal migration of birds. Univ. Kansas 

Publ. Mus. Natural History 3: 361–472.

Mabee, T. J. and B. A. Cooper. 2004. Nocturnal bird 

migration in northeastern Oregon and 

southeastern Washington. Northwestern 

Naturalist 85:39-47.

Mageau, M., B. Sunderland, and S. Stark. 2008. 

Minnesota’s Lake Superior coastal program 

wind resource development in the Minnesota 

coastal zone. University of Minnesota Center 

for Sustainable Community Development.

Project No. 306-02-08. Contract No. A92528.

McGuire, L. P., K. A. Jonasson, and C. G. Guglielmo. 

2012a. Torpor-assisted migration in bats. In: 

The Society for Integrated & Comparative 

Biology; January 4, 2012; Charleston, 

SC. Session 20.

McGuire, L. P., C. G. Guglielmo, S. A. Mackenzie, 

and P. D. Taylor. 2012b. Migratory stopover 

in the long-distance migrant silver-haired bat, 

Lasionycteris noctivagans. Journal of Animal 

Ecology 81: 377–385.

Mehlman, D. W., S. E. Mabey, D. N. Ewert, C. Duncan, 

B. Abel, D. Cimprich, R. D. Sutter, and 

M. Woodrey. 2005. Conserving stopover sites 

for forest-dwelling migratory landbirds. Auk 

122:1281-1290.

Moore, F.R., P. Kerlinger, T. R. Simons. 1990. Stopover 

on a Gulf Coast Barrier Island by fall trans-Gulf 

migrants. Wilson Bulletin. 102: 487-501.

Myres, M. T. 1964. Dawn ascent and reorientation of 

Scandanavian thrushes (Turdus spp.) migrating 

at night over the northeastern Atlantic Ocean in 

autumn. Ibis 106:7–51.

Newton, I. 2006. Can conditions experienced during 

migration limit the population levels of

birds? Journal of Ornithology 147:146-166.

Newton, I. 2007. Weather-related mass-mortality 

events in migrants. Ibis 149:453-467.

Newton, I. 2008. Migration ecology of birds. Academic 

Press, Elsevier. UK. 975 pp.

Peterson, A. and G. J. Niemi. 2011. Development of a 

comprehensive conservation strategy for 

the North Shore Highlands Region of 

Minnesota in the context of future wind 

development. Final Report. Natural Resources 

Research Institute technical report: 

NRRI/TR-2012/13.

Press, W. H., S. A. Teukolsky, W. T. Vetterling, and 

B. P. Flannery. 2007. Numerical Recipes: 

The Art of Scientific Computing (3rd ed.). 

New York: Cambridge University Press.

R Core Team. 2012. R: A language and environment 

for statistical computing. R Foundation 

for Statistical Computing, Vienna, Austria.

ISBN 3-900051-07-0, 

URL http://www.R-project.org/. 

Racey, P., and A. Entwistle. 2000. Life-history and 

reproductive strategies of bats.

Reproductive biology of bats, 363-414.

Rathbun, N.A., T. S., Bowden , R. L. Horton, 

D. C. Nolfi, E. C. Olson, D. J. Larson, and 

J. C. Gosse. 2016. Great Lakes Avian Radar 

Technical Report Niagara, Genesee, Wayne, 

and Jefferson Counties, New York. U.S. 

Department of Interior, Fish and Wildlife 

Service, Biological Technical Publication 

FWS/BTP-R3012-2016 

Rathbun, N.A., R. L. Horton, T. S., Bowden , 

D. C. Nolfi, E. C. Olson, D. J. Larson, and 

J. C. Gosse. 2017. Great Lakes Avian Radar 

Technical Report Lake County, MN, Bayfield 

County, WI, Keweenaw County Fall 2014.

U.S. Department of Interior, Fish and Wildlife 

Service, Biological Technical Publication

FWS/BTP-R3014-2017

Rich, T. D., C. J. Beardmore, H. Berlanga, 

P. J. Blancher, M. S. W. Bradstreet, 

G. S. Butcher, D. W. Demarest, E. H. Dunn, 

W. C. Hunter, E. E. Iñigo-Elias, J. A. Kennedy, 

A. M. Martell, A. O. Panjabi, D. N. Pashley, K. V. 

Rosenberg, C. M. Rustay, J. S. Wendt, T. C. Will. 

2004. Partners in Flight North American 

Landbird Conservation Plan. Cornell Lab 

of Ornithology. Ithaca, NY.

Ruth, J. M., editor. 2007. Applying radar technology 

to migratory bird conservation and 

management: strengthening and expanding 

a collaborative. Fort Collins, CO, U. S. 

Geological Survey, Biological Resources 

Discipline. Open-File Report 2007 – 1361, 

84p.

Schmaljohann, H., P. J. J. Becker, H. Karaardic, 

F. Liechti, B. Naef-Daenzer, and C. Grande. 

2011. Nocturnal exploratory flights, departure 

time, and direction in a migratory songbird.

Journal of Ornithology 152:439-452.
Great Lakes Avian Radar - Fall 2012 65

Schmaljohann, H., F. Liechti, E. Baechler, T. Steuri, 

and B. Bruderer. 2008. Quantification of bird 

migration by radar - a detection probability 

problem. Ibis 150:342-355.

Schmaljohann, H. and B. Naef-Daenzer. 2011. 

Body condition and wind support initiate the 

shift of migratory direction and timing of 

nocturnal departure in a songbird. Journal of 

Animal Ecology 80:1115-1122.

Sillett, T. S. and R. T. Holmes. 2002. Variation in 

survivorship of a migratory songbird 

throughout its annual cycle. Journal of 

Animal Ecology 71:296-308.

Smallwood, K.S. 2013. Comparing bird and bat fatalityrate estimates among North American windenergy projects. Wildlife Society 

Bulletin 37: 19-33.

Smallwood, K. S. and C. Thelander. 2008. Bird 

mortality in the Altamont Pass wind resource 

area, California. Journal of Wildlife 

Management 72:853-853.

Smith, R. J., M. J. Hamas, D. N. Ewert, and 

M. E. Dallman. 2004. Spatial foraging 

differences in American redstarts along 

the shoreline of northern Lake Huron during 

fall migration. Wilson Bulletin 116:48-55.

Smith, R. J., F. R. Moore, and C. A. May. 2007. 

Stopover habitat along the shoreline of northern 

Lake Huron, Michigan: Emergent aquatic 

insects as a food resource for fall migrating 

landbirds. Auk 124:107-121.

Taylor, P. D., S. A. Mackenzie, B. G. Thurber, 

A. M. Calvert, A. M. Mills, L. P. McGuire, 

and C. G. Guglielmo. 2011. Landscape 

Movements of Migratory Birds and Bats Reveal 

an Expanded Scale of Stopover. Plos One 6.

Timm, R.M. 1989. Migration and molt patterns of red 

bats. Illinois Bull. Chicago Academy of

Science.

Turner, G. G., D. M. Reeder, and J. T. H. Coleman. 

2011. A Five-year Assessment of Mortality and 

Geographic Spread of White-Nose Syndrome 

in North American Bats, with a Look at the 

Future. Update of White-Nose Syndrome in 

bats. Bat Research News, 52:13-27. 

U.S. Department of Energy. 2008. 20% Wind energy 

by 2030: increasing wind energy’s contribution 

to U.S. electricity supply. U.S. Department of 

Energy, Office of Scientific and Technical 

Information, Oak Ridge, Tennessee. <http://

www.nrel.gov/docs/fy08osti/41869.pdf> 

(accessed November 2013).

U.S. Department of Energy. 2015. Wind Vision: 

A New Era for Wind Power in the Uniter 

States. U.S. Department of Energy, Office 

of Scientific and Technical Information, Oak 

Ridge, Tennessee. http://www.energy.gov/sites/

prod/files/WindVision_Report_final.pdf 

(accessed August 2015)

USFWS. 2012. U.S. Fish and Wildlife land-based wind 

energy guidelines. OMB Control No. 1018-0148.

Wiedner, D. S., P. Kerlinger, D. A Sibley, P. Holt, 

J. Hough, and R. Cmssley. 1992. Visible morning

 flights of neotropical landbird migrants at Cape 

May, New Jersey. Auk 109 (3): 500-510.

Zar, J.H. 1999. Biostatistical Analysis, 4th ed. 

Prentice Hall, Upper Saddle River, NJ. 662 pp.
66 Great Lakes Avian Radar - Fall 2012 
Great Lakes Avian Radar - Fall 2012 67

Appendices

Appendix 1: Fall 2012 Report Summary

Appendix 2: Percent Land Cover Associated with Study Sites and the 2011 

 National Land Cover Database Classification

Appendix 3: Corrected Density per Hour by Biological Period

Appendix 4: Comparison of Static and Corrected Density Estimates
Appendix 1

Fall 2012 Report Summary

n Migration occurred at our four fall study sites 

• Migration occurred on the western and northern shoreline of Lake Michigan on both sides of 

 Green Bay during fall 2012 (West Delta County and Garden Peninsula sites)

• Migration occurred on the western shoreline of Lake Huron on both sides of Saginaw Bay during 

 fall 2012 (Iosco County and West Huron County sites)

• Migration is identified by uniformity of movement of direction (south) at night, high target passage 

 rate, and peaking of numbers a couple of hours before to a couple of hours after midnight 

• Patterns and timing of migration were similar between the paired sites

 • Lake Michigan sites:

 • A wave of migration occurred at our West Delta County and Garden Peninsula sites 

 beginning on August 27

 • Lake Huron sites:

 • Waves of migration occurred at our Iosco County and West Huron County sites early 

 September through mid/late October 

 • Highest concentrations occurred the first and last week of September

n Date range of pulses that occurred during the fall 2012 survey period 

• August 27 through September 1 at our Lake Michigan sites (September 1 was the last day of 

 the survey period)

• September 6 through mid/late October at our Lake Huron sites (survey period started on 

 September 2 and 6 at these sites) 

n Patterns of activity were different between Dawn, Day, Dusk, and Night time periods

• Movement south during the night: Lake Michigan sites

 • 52% of nights surveyed the mean direction of travel was generally southerly at our West 

 Delta County site

 • 62% of nights surveyed the mean direction of travel was generally southerly at our 

 Garden Peninsula site

• Movement south during the night: Lake Huron sites

 • 75% of nights surveyed the mean direction of travel was generally southerly at our Iosco 

 County site

 • 60% of nights surveyed the mean direction of travel was generally southerly at our 

 West Huron County site

• Movement in towards shore at dawn

 • Observed all sites

• Highest target passage rate at night 

• Dawn ascent

 • Increase in height around dawn hours observed at all sites

68 Great Lakes Avian Radar - Fall 2012 
n Peak density of targets in volume corrected counts

• Lake Michigan sites:

 • Max density below 150 m 14% of nights and 17% of night hours our West Delta County site 

 • Max density below 150 m 56% of nights and 55% of night hours at our Garden Peninsula site 

• Lake Huron sites:

 • Max density below 150 m 58% of nights and 50% of night hours our Iosco County site 

 • Max density below 150 m 36% of nights and 33% of night hours at our West Huron

 County site 

n Standards for radar studies need to be established, and recommendations are included in this report

 • Using radar counts as an index of activity and not a population estimate

 • Surveying continuously over the whole migration season

 • Examining smaller time periods (Dawn/Day/Dusk/Night or Hourly) rather than seasonal 

 metrics

 • Using volume corrected counts on the vertical radar to better estimate use of low altitudes and 

 the rotor swept zone

 • Using 50-m altitude bands to represent height distributions rather than mean or 

 median heights

 • Examining the most densely populated altitude bands rather than comparing numbers or 

 percentages of targets below, within, and above the rotor swept zone

 • Recognizing that migrants change altitude for various reasons over time and that targets 

 flying several altitude bands above the rotor swept zone may still be at risk.

Great Lakes Avian Radar - Fall 2012 69
Appendix 2

Percent Land Cover Associated with Study Sites

and the 2011 National Land Cover Database Classification

Land Cover Class

Percent Land Cover

West

Delta 

County

Garden 

Peninsula

Iosco 

County

West

Huron 

County

Cultivated crops/Hay pasture 3% 21% 5% 61%

Deciduous forest 6% 10% 10% 6%

Deveoloped1 4% 4% 8% 6%

Emergent herbaceous wetlands 2% 1% 7% 6%

Evergreen Forest 7% 18% 4% 0%

Mixed Forest 8% 10% 2% 0%

Open water 24% 7% 35% 10%

Other2 7% 8% 10% 1%

Woody wetlands 39% 22% 19% 9%

1 Includes low, medium and high intensity development and developed open space.

2 Includes barren land, herbaceous and shrub/scrub.

Percent land cover found within 3.7 km of radar locations at our West Delta County, Garden Peninsula, Iosco County, 

and West Huron County sites.

Classification Description for the 2011 National Land Cover Database 

(http://www.mrlc.gov/nlcd2011.php).

70 Great Lakes Avian Radar - Fall 2012 

Water

Open Water - areas of open water, generally with less than 25% cover of vegetation or soil.

Perennial Ice/Snow - area characterized by a perennial cover of ice and/or snow, generally 

greater than 25% of total cover.

Developed

Developed, Open Space - areas with a mixture of some constructed materials, but mostly 

vegetation in the form of lawn grasses. Impervious surfaces account for less than 20% of total 

cover, These areas most commonly include large-lot single family housing units, parks, golf 

courses, and vegetation planted in developed settings for recreation, erosion control, or aesthetic purposes.

Developed, Low Intensity - areas with a mixture of constructed materials and vegetation. 

Impervious surfaces account for 20% to 49% percent of total cover. These areas most commonly 

include single-family housing units.

Developed, Medium Intensity - areas with a mixture of constructed materials and vegetation. 

Impervious surfaces account for 50% to 79% of total cover. These areas most commonly include 

single-family housing units.

Developed, High Intesity - highly developed areas where people reside or work in high 

numbers. Examples include apartment complexes, row houses and commercial/industrial. 

Impervious surfaces account for 80% to 100% of the total cover.

Classification Description
(Appendix 2 continued)

Great Lakes Avian Radar - Fall 2012 71

Barren

Barren Land (Rock/Sand/Clay) - areas of bedrock, desert pavement, scarps, talus, slides, 

volcanic material, glacial debris, sand dunes, strip mines, gravel pits and other accumulations of 

earthen material. Generally, vegetation accounts for less than 15% of total cover.

Forest

Deciduous Forest - areas dominated by trees generally greater than 5 meters tall, and greater 

than 20% of total vegetation cover. More than 75% of the tree species shed foliage 

simultaneously in response to seasonal change.

Evergreen Forest - areas dominated by trees generally greater than 5 meters tall, and greater 

than 20% of total vegetation cover. More than 75% of the tree species maintain their leaves all 

year. Canopy is never without green foliage.

Mixed Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 

20% of total vegetation cover. Neither deciduous nor evergreen species are greater than 75% of 

total tree cover.

Shrubland

Dwarf Scrub - Alaska only areas dominated by shrubs less than 20 centimeters tall with shrub 

canopy typically greater than 20% of total vegetation. This type is often co-associated with 

grasses, sedges, herbs, and non-vascular vegetation.

Shrub/Scrub - areas dominated by shrubs; less than 5 meters tall with shrub canopy typically 

greater than 20% of total vegetation. This class includes true shrubs, young trees in an early 

successional stage or trees stunted from environmental conditions.

Herbaceous

Grassland/Herbaceous - areas dominated by gramanoid or herbaceous vegetation, generally 

greater than 80% of total vegetation. These areas are not subject to intensive management such 

as tilling, but can be utilized for grazing.

Sedge/Herbaceous - Alaska only areas dominated by sedges and forbs, generally greater than 

80% of total vegetation. This type can occur with significant other grasses or other grass like 

plants, and includes sedge tundra, and sedge tussock tundra.

Lichens - Alaska only areas dominated by fruticose or foliose lichens generally greater than 

80% of total vegetation.

Moss - Alaska only areas dominated by mosses, generally greater than 80% of total vegetation.

Planted/Cultivated

Pasture/Hay – areas of grasses, legumes, or grass-legume mixtures planted for livestock 

grazing or the production of seed or hay crops, typically on a perennial cycle. Pasture/hay 

vegetation accounts for greater than 20% of total vegetation.

Cultivated Crops – areas used for the production of annual crops, such as corn, soybeans, 

vegetables, tobacco, and cotton, and also perennial woody crops such as orchards and vineyards. 

Crop vegetation accounts for greater than 20% of total vegetation. This class also includes all 

land being actively tilled.

Wetlands

Woody Wetlands - areas where forest or shrubland vegetation accounts for greater than 20% of

vegetative cover and the soil or substrate is periodically saturated with or covered with water.

Emergent Herbaceous Wetlands - Areas where perennial herbaceous vegetation accounts for 

greater than 80% of vegetative cover and the soil or substrate is periodically saturated with or 

covered with water.
Appendix 3

Corrected Density per Hour by Biological Period

Altitude	

Band	(m) Dawn Day Dusk Night

50 0.1 0.1 0.1 0.2

100 0.5 0.3 0.4 1.3

150 0.3 0.2 0.3 1.7

200 0.4 0.3 0.7 3.3

250 0.3 0.2 0.6 3.0

300 0.4 0.1 0.4 2.8

350 0.4 0.1 0.5 3.1

400 0.3 0.1 0.4 2.7

450 0.5 0.1 0.3 2.5

500 0.5 0.1 0.3 2.2

550 0.4 0.1 0.2 1.9

600 0.4 0.0 0.1 1.5

650 0.5 0.0 0.1 1.5

700 0.4 0.0 0.1 1.3

750 0.5 0.0 0.1 1.3

800 0.4 0.0 0.0 1.0

850 0.2 0.0 0.0 0.8

900 0.3 0.0 0.0 0.7

950 0.2 0.0 0.0 0.5

1000 0.2 0.0 0.0 0.5

Altitude	

Band	(m) Dawn Day Dusk Night

50 0.4 0.2 0.2 1.5

100 0.6 0.6 0.5 2.8

150 0.6 0.7 0.5 3.1

200 0.6 0.5 0.4 3.2

250 0.7 0.4 0.4 3.0

300 0.8 0.2 0.3 3.0

350 0.7 0.2 0.2 2.7

400 0.4 0.1 0.3 2.6

450 0.7 0.1 0.2 2.5

500 0.8 0.1 0.1 2.2

550 0.6 0.1 0.1 1.8

600 0.4 0.1 0.1 1.5

650 0.4 0.1 0.1 1.2

700 0.3 0.0 0.0 1.0

750 0.3 0.0 0.0 0.8

800 0.3 0.0 0.0 0.7

850 0.2 0.0 0.0 0.6

900 0.2 0.0 0.0 0.5

950 0.2 0.0 0.0 0.4

1000 0.2 0.0 0.0 0.4

Estimated target density by altitude band during fall 

2012 biological time periods in West Delta County. 

Estimated target density by altitude band during fall 

2012 biological time periods in Garden Peninsula. 

72 Great Lakes Avian Radar - Fall 2012 
Altitude	

Band	(m) Dawn Day Dusk Night

50 0.2 0.1 0.1 0.2

100 1.4 0.5 0.3 3.7

150 1.0 0.3 0.2 5.2

200 0.9 0.3 0.3 6.0

250 0.8 0.3 0.3 5.4

300 0.8 0.3 0.3 4.9

350 1.0 0.4 0.3 5.1

400 0.8 0.3 0.2 4.2

450 0.7 0.2 0.2 3.9

500 0.6 0.2 0.1 3.3

550 0.5 0.1 0.1 2.8

600 0.4 0.1 0.1 2.5

650 0.3 0.1 0.1 2.1

700 0.2 0.0 0.1 1.8

750 0.2 0.0 0.0 1.6

800 0.2 0.0 0.0 1.3

850 0.1 0.0 0.0 1.1

900 0.1 0.0 0.0 0.9

950 0.1 0.0 0.0 0.8

1000 0.1 0.0 0.0 0.6

Altitude	

Band	(m) Dawn Day Dusk Night

50 0.0 0.1 0.0 0.0

100 1.1 1.0 0.7 1.1

150 1.0 0.6 0.8 2.4

200 0.9 0.4 0.5 2.8

250 0.6 0.3 0.3 2.9

300 0.5 0.2 0.2 2.8

350 0.6 0.2 0.2 3.1

400 0.6 0.1 0.1 2.6

450 0.4 0.1 0.1 2.2

500 0.4 0.1 0.1 1.9

550 0.3 0.1 0.0 1.7

600 0.2 0.0 0.0 1.5

650 0.2 0.0 0.0 1.2

700 0.2 0.0 0.0 1.1

750 0.2 0.0 0.0 0.9

800 0.1 0.0 0.0 0.7

850 0.1 0.0 0.0 0.6

900 0.1 0.0 0.0 0.5

950 0.1 0.0 0.0 0.3

1000 0.1 0.0 0.0 0.3

Estimated target density by altitude band during fall 

2012 biological time periods in Iosco County. 

Estimated target density by altitude band during fall 

2012 biological time periods in West Huron County. 

Great Lakes Avian Radar - Fall 2012 73
Appendix 4

Comparison of Static and Corrected Density Estimates

Comparison of methods to estimated target density by altitude band during the dawn biological period in West 

Delta County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 16 16 31.3 5.6 0.0 0.1 0.7% 0.7% 1.8%

100 65 81 31.3 5.9 0.1 0.5 3.0% 3.0% 6.8%

150 38 119 31.3 6.5 0.1 0.3 1.8% 1.8% 3.6%

200 66 185 31.3 7.1 0.1 0.4 3.0% 3.0% 5.7%

250 58 243 31.3 7.9 0.1 0.3 2.7% 2.7% 4.5%

300 71 314 31.3 8.5 0.1 0.4 3.3% 3.3% 5.2%

350 82 396 31.3 9.5 0.1 0.4 3.8% 3.8% 5.4%

400 76 472 31.3 10.3 0.1 0.3 3.5% 3.5% 4.5%

450 113 585 31.3 11.2 0.2 0.5 5.2% 5.2% 6.2%

500 138 723 31.3 12.2 0.2 0.5 6.4% 6.4% 7.0%

550 121 844 31.3 13.3 0.2 0.4 5.6% 5.6% 5.6%

600 116 960 31.3 14.1 0.2 0.4 5.4% 5.4% 5.1%

650 152 1,112 31.3 15.3 0.2 0.5 7.0% 7.0% 6.1%

700 124 1,236 31.3 16.2 0.2 0.4 5.7% 5.7% 4.7%

750 201 1,437 31.3 17.2 0.3 0.5 9.3% 9.3% 7.2%

800 151 1,588 31.3 18.2 0.2 0.4 7.0% 7.0% 5.1%

850 96 1,684 31.3 19.4 0.1 0.2 4.4% 4.4% 3.1%

900 112 1,796 31.3 20.4 0.2 0.3 5.2% 5.2% 3.4%

950 70 1,866 31.3 21.4 0.1 0.2 3.2% 3.2% 2.0%

1,000 74 1,940 31.3 22.4 0.1 0.2 3.4% 3.4% 2.0% 1 Total target counts recorded up to the 2,800 m band during the dawn time period was 2,168.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 7.55.

74 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the day biological period in West Delta 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 122 122 31.3 5.6 0.0 0.1 2.3% 2.3% 1.1%

100 421 543 31.3 5.9 0.1 0.3 8.0% 8.0% 3.7%

150 351 894 31.3 6.5 0.0 0.2 6.6% 6.6% 2.8%

200 516 1,410 31.3 7.1 0.1 0.3 9.8% 9.8% 3.8%

250 328 1,738 31.3 7.9 0.0 0.2 6.2% 6.2% 2.2%

300 246 1,984 31.3 8.5 0.0 0.1 4.7% 4.7% 1.5%

350 303 2,287 31.3 9.5 0.0 0.1 5.7% 5.7% 1.7%

400 261 2,548 31.3 10.3 0.0 0.1 4.9% 4.9% 1.3%

450 396 2,944 31.3 11.2 0.0 0.1 7.5% 7.5% 1.8%

500 376 3,320 31.3 12.2 0.0 0.1 7.1% 7.1% 1.6%

550 243 3,563 31.3 13.3 0.0 0.1 4.6% 4.6% 1.0%

600 151 3,714 31.3 14.1 0.0 0.0 2.9% 2.9% 0.6%

650 152 3,866 31.3 15.3 0.0 0.0 2.9% 2.9% 0.5%

700 154 4,020 31.3 16.2 0.0 0.0 2.9% 2.9% 0.5%

750 167 4,187 31.3 17.2 0.0 0.0 3.2% 3.2% 0.5%

800 124 4,311 31.3 18.2 0.0 0.0 2.3% 2.3% 0.4%

850 103 4,414 31.3 19.4 0.0 0.0 2.0% 2.0% 0.3%

900 105 4,519 31.3 20.4 0.0 0.0 2.0% 2.0% 0.3%

950 86 4,605 31.3 21.4 0.0 0.0 1.6% 1.6% 0.2%

1,000 82 4,687 31.3 22.4 0.0 0.0 1.6% 1.6% 0.2% 1 Total target counts recorded up to the 2,800 m band during the day time period was 5,280.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 2.02.

Great Lakes Avian Radar - Fall 2012 75
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dusk biological period in West Delta 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 12 12 31.3 5.6 0.0 0.1 1.3% 1.3% 2.3%

100 50 62 31.3 5.9 0.1 0.4 5.4% 5.4% 8.9%

150 38 100 31.3 6.5 0.1 0.3 4.1% 4.1% 6.2%

200 98 198 31.3 7.1 0.2 0.7 10.6% 10.6% 14.6%

250 91 289 31.3 7.9 0.1 0.6 9.8% 9.8% 12.1%

300 75 364 31.3 8.5 0.1 0.4 8.1% 8.1% 9.3%

350 93 457 31.3 9.5 0.1 0.5 10.0% 10.0% 10.4%

400 79 536 31.3 10.3 0.1 0.4 8.5% 8.5% 8.1%

450 74 610 31.3 11.2 0.1 0.3 8.0% 8.0% 7.0%

500 79 689 31.3 12.2 0.1 0.3 8.5% 8.5% 6.8%

550 51 740 31.3 13.3 0.1 0.2 5.5% 5.5% 4.0%

600 31 771 31.3 14.1 0.0 0.1 3.3% 3.3% 2.3%

650 35 806 31.3 15.3 0.1 0.1 3.8% 3.8% 2.4%

700 23 829 31.3 16.2 0.0 0.1 2.5% 2.5% 1.5%

750 24 853 31.3 17.2 0.0 0.1 2.6% 2.6% 1.5%

800 5 858 31.3 18.2 0.0 0.0 0.5% 0.5% 0.3%

850 3 861 31.3 19.4 0.0 0.0 0.3% 0.3% 0.2%

900 11 872 31.3 20.4 0.0 0.0 1.2% 1.2% 0.6%

950 5 877 31.3 21.4 0.0 0.0 0.5% 0.5% 0.2%

1,000 5 882 31.3 22.4 0.0 0.0 0.5% 0.5% 0.0% 1 Total target counts recorded up to the 2,800 m band during the dusk time period was 926. 2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 4.57.

76 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the night biological period in West Delta 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 192 192 31.3 5.6 0.0 0.2 0.2% 0.2% 0.5%

100 1,534 1,726 31.3 5.9 0.2 1.3 1.8% 1.8% 3.7%

150 2,182 3,908 31.3 6.5 0.4 1.7 2.6% 2.6% 4.9%

200 4,554 8,462 31.3 7.1 0.7 3.3 5.5% 5.5% 9.3%

250 4,730 13,192 31.3 7.9 0.8 3.0 5.7% 5.7% 8.7%

300 4,607 17,799 31.3 8.5 0.7 2.8 5.5% 5.5% 7.9%

350 5,755 23,554 31.3 9.5 0.9 3.1 6.9% 6.9% 8.8%

400 5,469 29,023 31.3 10.3 0.9 2.7 6.6% 6.6% 7.7%

450 5,537 34,560 31.3 11.2 0.9 2.5 6.6% 6.6% 7.1%

500 5,410 39,970 31.3 12.2 0.9 2.2 6.5% 6.5% 6.4%

550 4,944 44,914 31.3 13.3 0.8 1.9 5.9% 5.9% 5.4%

600 4,175 49,089 31.3 14.1 0.7 1.5 5.0% 5.0% 4.3%

650 4,421 53,510 31.3 15.3 0.7 1.5 5.3% 5.3% 4.2%

700 4,226 57,736 31.3 16.2 0.7 1.3 5.1% 5.1% 3.8%

750 4,279 62,015 31.3 17.2 0.7 1.3 5.1% 5.1% 3.6%

800 3,698 65,713 31.3 18.2 0.6 1.0 4.4% 4.4% 2.9%

850 3,092 68,805 31.3 19.4 0.5 0.8 3.7% 3.7% 2.3%

900 2,706 71,511 31.3 20.4 0.4 0.7 3.2% 3.2% 1.9%

950 2,194 73,705 31.3 21.4 0.4 0.5 2.6% 2.6% 1.5%

1,000 2,010 75,715 31.3 22.4 0.3 0.5 2.4% 2.4% 1.3% 1 Total target counts recorded up to the 2,800 m band during the night time period was 83,384.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 35.02.

Great Lakes Avian Radar - Fall 2012 77
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dawn biological period in Garden 

Peninsula, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 51 51 31.3 5.6 0.1 0.4 1.9% 1.9% 4.1%

100 86 137 31.3 5.9 0.1 0.6 3.3% 3.3% 6.5%

150 91 228 31.3 6.5 0.1 0.6 3.5% 3.5% 6.4%

200 98 326 31.3 7.1 0.1 0.6 3.7% 3.7% 6.2%

250 127 453 31.3 7.9 0.2 0.7 4.8% 4.8% 7.3%

300 160 613 31.3 8.5 0.2 0.8 6.1% 6.1% 8.5%

350 146 759 31.3 9.5 0.2 0.7 5.6% 5.6% 7.0%

400 87 846 31.3 10.3 0.1 0.4 3.3% 3.3% 3.8%

450 178 1,024 31.3 11.2 0.3 0.7 6.8% 6.8% 7.2%

500 217 1,241 31.3 12.2 0.3 0.8 8.3% 8.3% 8.0%

550 169 1,410 31.3 13.3 0.2 0.6 6.4% 6.4% 5.7%

600 134 1,544 31.3 14.1 0.2 0.4 5.1% 5.1% 4.3%

650 125 1,669 31.3 15.3 0.2 0.4 4.8% 4.8% 3.7%

700 127 1,796 31.3 16.2 0.2 0.3 4.8% 4.8% 3.5%

750 111 1,907 31.3 17.2 0.2 0.3 4.2% 4.2% 2.9%

800 117 2,024 31.3 18.2 0.2 0.3 4.5% 4.5% 2.9%

850 100 2,124 31.3 19.4 0.1 0.2 3.8% 3.8% 2.3%

900 90 2,214 31.3 20.4 0.1 0.2 3.4% 3.4% 2.0%

950 100 2,314 31.3 21.4 0.1 0.2 3.8% 3.8% 2.1%

1,000 77 2,391 31.3 22.4 0.1 0.2 2.9% 2.9% 1.6% 1 Total target counts recorded up to the 2,800 m band during the dawn time period was 2,626. 2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 9.74.

78 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the day biological period in Garden 

Peninsula, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 341 341 31.3 5.6 0.0 0.2 4.3% 4.3% 2.4%

100 911 1,252 31.3 5.9 0.1 0.6 11.4% 11.4% 6.1%

150 1,174 2,426 31.3 6.5 0.1 0.7 14.7% 14.7% 7.2%

200 939 3,365 31.3 7.1 0.1 0.5 11.8% 11.8% 5.2%

250 731 4,096 31.3 7.9 0.1 0.4 9.2% 9.2% 3.7%

300 536 4,632 31.3 8.5 0.1 0.2 6.7% 6.7% 2.5%

350 409 5,041 31.3 9.5 0.1 0.2 5.1% 5.1% 1.7%

400 268 5,309 31.3 10.3 0.0 0.1 3.4% 3.4% 1.0%

450 354 5,663 31.3 11.2 0.0 0.1 4.4% 4.4% 1.2%

500 429 6,092 31.3 12.2 0.1 0.1 5.4% 5.4% 1.4%

550 353 6,445 31.3 13.3 0.0 0.1 4.4% 4.4% 1.1%

600 253 6,698 31.3 14.1 0.0 0.1 3.2% 3.2% 0.7%

650 212 6,910 31.3 15.3 0.0 0.1 2.7% 2.7% 0.5%

700 175 7,085 31.3 16.2 0.0 0.0 2.2% 2.2% 0.4%

750 169 7,254 31.3 17.2 0.0 0.0 2.1% 2.1% 0.4%

800 143 7,397 31.3 18.2 0.0 0.0 1.8% 1.8% 0.3%

850 93 7,490 31.3 19.4 0.0 0.0 1.2% 1.2% 0.2%

900 80 7,570 31.3 20.4 0.0 0.0 1.0% 1.0% 0.2%

950 66 7,636 31.3 21.4 0.0 0.0 0.8% 0.8% 0.1%

1,000 46 7,682 31.3 22.4 0.0 0.0 0.6% 0.6% 0.1% 1 Total target counts recorded up to the 2,800 m band during the day time period was 7,988.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 3.59.

Great Lakes Avian Radar - Fall 2012 79
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dusk biological period in Garden 

Peninsula, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 24 24 31.3 5.6 0.0 0.2 3.5% 3.5% 5.7%

100 61 85 31.3 5.9 0.1 0.5 9.0% 9.0% 13.7%

150 71 156 31.3 6.5 0.1 0.5 10.5% 10.5% 14.7%

200 62 218 31.3 7.1 0.1 0.4 9.1% 9.1% 11.7%

250 63 281 31.3 7.9 0.1 0.4 9.3% 9.3% 10.7%

300 54 335 31.3 8.5 0.1 0.3 8.0% 8.0% 8.5%

350 48 383 31.3 9.5 0.1 0.2 7.1% 7.1% 6.8%

400 57 440 31.3 10.3 0.1 0.3 8.4% 8.4% 7.4%

450 37 477 31.3 11.2 0.1 0.2 5.4% 5.4% 4.4%

500 34 511 31.3 12.2 0.1 0.1 5.0% 5.0% 3.7%

550 29 540 31.3 13.3 0.0 0.1 4.3% 4.3% 2.9%

600 19 559 31.3 14.1 0.0 0.1 2.8% 2.8% 1.8%

650 18 577 31.3 15.3 0.0 0.1 2.7% 2.7% 1.6%

700 12 589 31.3 16.2 0.0 0.0 1.8% 1.8% 1.0%

750 11 600 31.3 17.2 0.0 0.0 1.6% 1.6% 0.9%

800 8 608 31.3 18.2 0.0 0.0 1.2% 1.2% 0.6%

850 13 621 31.3 19.4 0.0 0.0 1.9% 1.9% 0.9%

900 18 639 31.3 20.4 0.0 0.0 2.7% 2.7% 1.2%

950 6 645 31.3 21.4 0.0 0.0 0.9% 0.9% 0.4%

1,000 6 651 31.3 22.4 0.0 0.0 0.9% 0.9% 0.0% 1 Total target counts recorded up to the 2,800 m band during the dusk time period was 679.

2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 3.5.

80 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the night biological period in Garden 

Peninsula, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 1,690 1,690 31.3 5.6 0.3 1.5 2.0% 2.0% 4.0%

100 3,476 5,166 31.3 5.9 0.5 2.8 4.2% 4.2% 7.7%

150 4,086 9,252 31.3 6.5 0.6 3.1 4.9% 4.9% 8.4%

200 4,703 13,955 31.3 7.1 0.7 3.2 5.6% 5.6% 8.8%

250 4,970 18,925 31.3 7.9 0.8 3.0 6.0% 6.0% 8.3%

300 5,241 24,166 31.3 8.5 0.8 3.0 6.3% 6.3% 8.2%

350 5,239 29,405 31.3 9.5 0.8 2.7 6.3% 6.3% 7.3%

400 5,446 34,851 31.3 10.3 0.8 2.6 6.5% 6.5% 7.0%

450 5,800 40,651 31.3 11.2 0.9 2.5 7.0% 7.0% 6.8%

500 5,572 46,223 31.3 12.2 0.9 2.2 6.7% 6.7% 6.0%

550 4,970 51,193 31.3 13.3 0.8 1.8 6.0% 6.0% 4.9%

600 4,257 55,450 31.3 14.1 0.7 1.5 5.1% 5.1% 4.0%

650 3,651 59,101 31.3 15.3 0.6 1.2 4.4% 4.4% 3.2%

700 3,321 62,422 31.3 16.2 0.5 1.0 4.0% 4.0% 2.7%

750 2,899 65,321 31.3 17.2 0.4 0.8 3.5% 3.5% 2.2%

800 2,526 67,847 31.3 18.2 0.4 0.7 3.0% 3.0% 1.8%

850 2,276 70,123 31.3 19.4 0.4 0.6 2.7% 2.7% 1.6%

900 2,174 72,297 31.3 20.4 0.3 0.5 2.6% 2.6% 1.4%

950 1,821 74,118 31.3 21.4 0.3 0.4 2.2% 2.2% 1.1%

1,000 1,627 75,745 31.3 22.4 0.3 0.4 2.0% 2.0% 1.0% 1 Total target counts recorded up to the 2,800 m band during the night time period was 83,259.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 36.63.

Great Lakes Avian Radar - Fall 2012 81
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dawn biological period in Iosco 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 70 70 31.3 5.6 0.0 0.2 1.1% 1.1% 2.0%

100 470 540 31.3 5.9 0.3 1.4 7.3% 7.3% 13.0%

150 376 916 31.3 6.5 0.2 1.0 5.8% 5.8% 9.5%

200 358 1,274 31.3 7.1 0.2 0.9 5.5% 5.5% 8.3%

250 346 1,620 31.3 7.9 0.2 0.8 5.3% 5.3% 7.2%

300 366 1,986 31.3 8.5 0.2 0.8 5.7% 5.7% 7.1%

350 537 2,523 31.3 9.5 0.3 1.0 8.3% 8.3% 9.3%

400 438 2,961 31.3 10.3 0.2 0.8 6.8% 6.8% 7.0%

450 443 3,404 31.3 11.2 0.3 0.7 6.8% 6.8% 6.5%

500 415 3,819 31.3 12.2 0.2 0.6 6.4% 6.4% 5.6%

550 394 4,213 31.3 13.3 0.2 0.5 6.1% 6.1% 4.9%

600 329 4,542 31.3 14.1 0.2 0.4 5.1% 5.1% 3.8%

650 295 4,837 31.3 15.3 0.2 0.3 4.6% 4.6% 3.2%

700 205 5,042 31.3 16.2 0.1 0.2 3.2% 3.2% 2.1%

750 218 5,260 31.3 17.2 0.1 0.2 3.4% 3.4% 2.1%

800 154 5,414 31.3 18.2 0.1 0.2 2.4% 2.4% 1.4%

850 159 5,573 31.3 19.4 0.1 0.1 2.5% 2.5% 1.3%

900 131 5,704 31.3 20.4 0.1 0.1 2.0% 2.0% 1.1%

950 117 5,821 31.3 21.4 0.1 0.1 1.8% 1.8% 0.9%

1,000 125 5,946 31.3 22.4 0.1 0.1 1.9% 1.9% 0.9% 1 Total target counts recorded up to the 2,800 m band during the dawn time period was 6,470.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 10.86.

82 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the day biological period in Iosco 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% Corrected 

Density

50 355 355 31.3 5.6 0.0 0.1 2.0% 2.0% 1.0%

100 1,680 2,035 31.3 5.9 0.1 0.5 9.5% 9.5% 4.5%

150 1,118 3,153 31.3 6.5 0.1 0.3 6.3% 6.3% 2.8%

200 1,431 4,584 31.3 7.1 0.1 0.3 8.1% 8.1% 3.2%

250 1,263 5,847 31.3 7.9 0.1 0.3 7.1% 7.1% 2.5%

300 1,264 7,111 31.3 8.5 0.1 0.3 7.1% 7.1% 2.4%

350 1,961 9,072 31.3 9.5 0.1 0.4 11.0% 11.0% 3.3%

400 1,579 10,651 31.3 10.3 0.1 0.3 8.9% 8.9% 2.4%

450 1,556 12,207 31.3 11.2 0.1 0.2 8.8% 8.8% 2.2%

500 1,197 13,404 31.3 12.2 0.1 0.2 6.7% 6.7% 1.6%

550 890 14,294 31.3 13.3 0.0 0.1 5.0% 5.0% 1.1%

600 776 15,070 31.3 14.1 0.0 0.1 4.4% 4.4% 0.9%

650 504 15,574 31.3 15.3 0.0 0.1 2.8% 2.8% 0.5%

700 427 16,001 31.3 16.2 0.0 0.0 2.4% 2.4% 0.4%

750 345 16,346 31.3 17.2 0.0 0.0 1.9% 1.9% 0.3%

800 266 16,612 31.3 18.2 0.0 0.0 1.5% 1.5% 0.2%

850 204 16,816 31.3 19.4 0.0 0.0 1.1% 1.1% 0.2%

900 143 16,959 31.3 20.4 0.0 0.0 0.8% 0.8% 0.1%

950 107 17,066 31.3 21.4 0.0 0.0 0.6% 0.6% 0.1%

1,000 87 17,153 31.3 22.4 0.0 0.0 0.5% 0.5% 0.1% 1 Total target counts recorded up to the 2,800 m band during the day time period was 17,754.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 3.27.

Great Lakes Avian Radar - Fall 2012 83
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dusk biological period in Iosco 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% Corrected 

Density

50 27 27 31.3 5.6 0.0 0.1 1.7% 1.7% 3.2%

100 96 123 31.3 5.9 0.1 0.3 6.1% 6.1% 10.7%

150 66 189 31.3 6.5 0.0 0.2 4.2% 4.2% 6.7%

200 116 305 31.3 7.1 0.1 0.3 7.4% 7.4% 10.8%

250 117 422 31.3 7.9 0.1 0.3 7.4% 7.4% 9.8%

300 125 547 31.3 8.5 0.1 0.3 7.9% 7.9% 9.7%

350 143 690 31.3 9.5 0.1 0.3 9.1% 9.1% 10.0%

400 126 816 31.3 10.3 0.1 0.2 8.0% 8.0% 8.1%

450 100 916 31.3 11.2 0.1 0.2 6.3% 6.3% 5.9%

500 66 982 31.3 12.2 0.0 0.1 4.2% 4.2% 3.6%

550 81 1,063 31.3 13.3 0.0 0.1 5.1% 5.1% 4.0%

600 64 1,127 31.3 14.1 0.0 0.1 4.1% 4.1% 3.0%

650 64 1,191 31.3 15.3 0.0 0.1 4.1% 4.1% 2.8%

700 47 1,238 31.3 16.2 0.0 0.1 3.0% 3.0% 1.9%

750 33 1,271 31.3 17.2 0.0 0.0 2.1% 2.1% 1.3%

800 41 1,312 31.3 18.2 0.0 0.0 2.6% 2.6% 1.5%

850 28 1,340 31.3 19.4 0.0 0.0 1.8% 1.8% 1.0%

900 35 1,375 31.3 20.4 0.0 0.0 2.2% 2.2% 1.1%

950 20 1,395 31.3 21.4 0.0 0.0 1.3% 1.3% 0.6%

1,000 27 1,422 31.3 22.4 0.0 0.0 1.7% 1.7% 0.0% 1 Total target counts recorded up to the 2,800 m band during the dusk time period was 1,577. 2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 2.62.

84 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the night biological period in Iosco 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 869 869 31.3 5.6 0.0 0.2 0.2% 0.2% 0.4%

100 14,541 15,410 31.3 5.9 0.7 3.7 3.3% 3.3% 6.3%

150 21,969 37,379 31.3 6.5 1.1 5.2 5.0% 5.0% 8.7%

200 28,116 65,495 31.3 7.1 1.4 6.0 6.4% 6.4% 10.2%

250 28,268 93,763 31.3 7.9 1.4 5.4 6.5% 6.5% 9.2%

300 27,456 121,219 31.3 8.5 1.3 4.9 6.3% 6.3% 8.3%

350 31,728 152,947 31.3 9.5 1.5 5.1 7.3% 7.3% 8.6%

400 28,638 181,585 31.3 10.3 1.4 4.2 6.6% 6.6% 7.1%

450 28,503 210,088 31.3 11.2 1.4 3.9 6.5% 6.5% 6.5%

500 26,347 236,435 31.3 12.2 1.3 3.3 6.0% 6.0% 5.5%

550 24,736 261,171 31.3 13.3 1.2 2.8 5.7% 5.7% 4.8%

600 22,825 283,996 31.3 14.1 1.1 2.5 5.2% 5.2% 4.1%

650 21,435 305,431 31.3 15.3 1.0 2.1 4.9% 4.9% 3.6%

700 19,714 325,145 31.3 16.2 1.0 1.8 4.5% 4.5% 3.1%

750 17,637 342,782 31.3 17.2 0.9 1.6 4.0% 4.0% 2.6%

800 15,461 358,243 31.3 18.2 0.8 1.3 3.5% 3.5% 2.2%

850 13,464 371,707 31.3 19.4 0.7 1.1 3.1% 3.1% 1.8%

900 12,292 383,999 31.3 20.4 0.6 0.9 2.8% 2.8% 1.5%

950 10,554 394,553 31.3 21.4 0.5 0.8 2.4% 2.4% 1.3%

1,000 8,901 403,454 31.3 22.4 0.4 0.6 2.0% 2.0% 1.0% 1 Total target counts recorded up to the 2,800 m band during the night time period was 436,554.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 59.31.

Great Lakes Avian Radar - Fall 2012 85
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dawn biological period in West 

Huron County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 15 15 31.3 5.6 0.0 0.0 0.3% 0.3% 0.6%

100 390 405 31.3 5.9 0.2 1.1 8.3% 8.3% 14.3%

150 388 793 31.3 6.5 0.2 1.0 8.3% 8.3% 13.1%

200 389 1,182 31.3 7.1 0.2 0.9 8.3% 8.3% 12.0%

250 259 1,441 31.3 7.9 0.1 0.6 5.5% 5.5% 7.1%

300 230 1,671 31.3 8.5 0.1 0.5 4.9% 4.9% 5.9%

350 324 1,995 31.3 9.5 0.2 0.6 6.9% 6.9% 7.5%

400 331 2,326 31.3 10.3 0.2 0.6 7.0% 7.0% 7.0%

450 254 2,580 31.3 11.2 0.1 0.4 5.4% 5.4% 4.9%

500 258 2,838 31.3 12.2 0.1 0.4 5.5% 5.5% 4.6%

550 230 3,068 31.3 13.3 0.1 0.3 4.9% 4.9% 3.8%

600 199 3,267 31.3 14.1 0.1 0.2 4.2% 4.2% 3.1%

650 187 3,454 31.3 15.3 0.1 0.2 4.0% 4.0% 2.7%

700 199 3,653 31.3 16.2 0.1 0.2 4.2% 4.2% 2.7%

750 165 3,818 31.3 17.2 0.1 0.2 3.5% 3.5% 2.1%

800 130 3,948 31.3 18.2 0.1 0.1 2.8% 2.8% 1.6%

850 130 4,078 31.3 19.4 0.1 0.1 2.8% 2.8% 1.5%

900 121 4,199 31.3 20.4 0.1 0.1 2.6% 2.6% 1.3%

950 116 4,315 31.3 21.4 0.1 0.1 2.5% 2.5% 1.2%

1,000 78 4,393 31.3 22.4 0.0 0.1 1.7% 1.7% 0.8% 1 Total target counts recorded up to the 2,800 m band during the dawn time period was 4,696. 2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 7.89.

86 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the day biological period in West Huron 

County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 196 196 31.3 5.6 0.0 0.1 1.1% 1.1% 0.7%

100 3,739 3,935 31.3 5.9 0.2 1.0 21.3% 21.3% 12.8%

150 2,569 6,504 31.3 6.5 0.1 0.6 14.7% 14.7% 8.1%

200 1,886 8,390 31.3 7.1 0.1 0.4 10.8% 10.8% 5.4%

250 1,423 9,813 31.3 7.9 0.1 0.3 8.1% 8.1% 3.7%

300 1,052 10,865 31.3 8.5 0.1 0.2 6.0% 6.0% 2.5%

350 1,069 11,934 31.3 9.5 0.1 0.2 6.1% 6.1% 2.3%

400 856 12,790 31.3 10.3 0.0 0.1 4.9% 4.9% 1.7%

450 717 13,507 31.3 11.2 0.0 0.1 4.1% 4.1% 1.3%

500 557 14,064 31.3 12.2 0.0 0.1 3.2% 3.2% 0.9%

550 476 14,540 31.3 13.3 0.0 0.1 2.7% 2.7% 0.7%

600 360 14,900 31.3 14.1 0.0 0.0 2.1% 2.1% 0.5%

650 344 15,244 31.3 15.3 0.0 0.0 2.0% 2.0% 0.5%

700 291 15,535 31.3 16.2 0.0 0.0 1.7% 1.7% 0.4%

750 278 15,813 31.3 17.2 0.0 0.0 1.6% 1.6% 0.3%

800 249 16,062 31.3 18.2 0.0 0.0 1.4% 1.4% 0.3%

850 222 16,284 31.3 19.4 0.0 0.0 1.3% 1.3% 0.2%

900 264 16,548 31.3 20.4 0.0 0.0 1.5% 1.5% 0.3%

950 213 16,761 31.3 21.4 0.0 0.0 1.2% 1.2% 0.2%

1,000 188 16,949 31.3 22.4 0.0 0.0 1.1% 1.1% 0.2% 1 Total target counts recorded up to the 2,800 m band during the day time period was 17,529. 2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 3.41.

Great Lakes Avian Radar - Fall 2012 87
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the dusk biological period in West 

Huron County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 4 4 31.3 5.6 0.0 0.0 0.3% 0.3% 0.4%

100 246 250 31.3 5.9 0.1 0.7 16.2% 16.2% 22.1%

150 292 542 31.3 6.5 0.2 0.8 19.3% 19.3% 24.1%

200 210 752 31.3 7.1 0.1 0.5 13.9% 13.9% 15.8%

250 152 904 31.3 7.9 0.1 0.3 10.0% 10.0% 10.2%

300 109 1,013 31.3 8.5 0.1 0.2 7.2% 7.2% 6.8%

350 105 1,118 31.3 9.5 0.1 0.2 6.9% 6.9% 5.9%

400 90 1,208 31.3 10.3 0.0 0.1 5.9% 5.9% 4.6%

450 40 1,248 31.3 11.2 0.0 0.1 2.6% 2.6% 1.9%

500 42 1,290 31.3 12.2 0.0 0.1 2.8% 2.8% 1.8%

550 30 1,320 31.3 13.3 0.0 0.0 2.0% 2.0% 1.2%

600 30 1,350 31.3 14.1 0.0 0.0 2.0% 2.0% 1.1%

650 19 1,369 31.3 15.3 0.0 0.0 1.3% 1.3% 0.7%

700 17 1,386 31.3 16.2 0.0 0.0 1.1% 1.1% 0.6%

750 14 1,400 31.3 17.2 0.0 0.0 0.9% 0.9% 0.4%

800 8 1,408 31.3 18.2 0.0 0.0 0.5% 0.5% 0.2%

850 13 1,421 31.3 19.4 0.0 0.0 0.9% 0.9% 0.4%

900 12 1,433 31.3 20.4 0.0 0.0 0.8% 0.8% 0.3%

950 8 1,441 31.3 21.4 0.0 0.0 0.5% 0.5% 0.2%

1,000 9 1,450 31.3 22.4 0.0 0.0 0.6% 0.6% 0.0% 1 Total target counts recorded up to the 2,800 m band during the dusk time period was 1,514. 2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 3.13.

88 Great Lakes Avian Radar - Fall 2012 
(Appendix 4 continued)

Comparison of methods to estimated target density by altitude band during the night biological period in West 

Huron County, fall 2012.

Altitude 

Band 

(m)

Target 

Count

Running 

Total 

Target 

Count1

Static 

Volume

Corrected 

Volume

Static 

Target 

Density 

per Hour

Corrected 

Target 

Density per 

Hour2

% Total 

Targets

% Static 

Density

% 

Corrected 

Density

50 157 157 31.3 5.6 0.0 0.0 0.1% 0.1% 0.1%

100 4,495 4,652 31.3 5.9 0.2 1.1 1.9% 1.9% 3.6%

150 10,383 15,035 31.3 6.5 0.5 2.4 4.4% 4.4% 7.7%

200 13,306 28,341 31.3 7.1 0.6 2.8 5.7% 5.7% 8.9%

250 15,242 43,583 31.3 7.9 0.7 2.9 6.5% 6.5% 9.2%

300 16,282 59,865 31.3 8.5 0.8 2.8 6.9% 6.9% 9.1%

350 19,719 79,584 31.3 9.5 0.9 3.1 8.4% 8.4% 9.9%

400 18,052 97,636 31.3 10.3 0.9 2.6 7.7% 7.7% 8.3%

450 17,015 114,651 31.3 11.2 0.8 2.2 7.2% 7.2% 7.2%

500 15,908 130,559 31.3 12.2 0.8 1.9 6.8% 6.8% 6.2%

550 15,102 145,661 31.3 13.3 0.7 1.7 6.4% 6.4% 5.4%

600 14,142 159,803 31.3 14.1 0.7 1.5 6.0% 6.0% 4.8%

650 12,805 172,608 31.3 15.3 0.6 1.2 5.4% 5.4% 4.0%

700 11,611 184,219 31.3 16.2 0.5 1.1 4.9% 4.9% 3.4%

750 10,128 194,347 31.3 17.2 0.5 0.9 4.3% 4.3% 2.8%

800 8,905 203,252 31.3 18.2 0.4 0.7 3.8% 3.8% 2.3%

850 7,660 210,912 31.3 19.4 0.4 0.6 3.3% 3.3% 1.9%

900 6,437 217,349 31.3 20.4 0.3 0.5 2.7% 2.7% 1.5%

950 4,772 222,121 31.3 21.4 0.2 0.3 2.0% 2.0% 1.1%

1,000 3,800 225,921 31.3 22.4 0.2 0.3 1.6% 1.6% 0.8% 1 Total target counts recorded up to the 2,800 m band during the night time period was 235,486. 2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 31.03.

Great Lakes Avian Radar - Fall 2012 89
Fall 2012