Great Lakes Avian Radar

Technical Report

Lake Huron Shoreline:

Presque Isle County and Alcona County, MI

Fall 2015 and Spring 2016

U.S. Fish & Wildlife Service

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Avian Report.indd 2 7/24/18 6:2
Great Lakes Avian Radar 

Technical Report

Lake Huron Shoreline: 

Presque Isle County 

and Alcona County, MI

Fall 2015 and Spring 2016

U.S. Fish and Wildlife Service, Region 3

Funding Provided by Great Lakes Restoration Initiative

March 2018

Principle Investigator

Jeff Gosse, Regional Energy Coordinator, USFWS Region 3

Authors

Michael Wells, Fish and Wildlife Biologist, USFWS Region 3

Kevin Heist, Fish and Wildlife Biologist, USFWS Region 3

Rebecca Horton, 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

Nathan Rathbun, Fish and Wildlife Biologist, USFWS Region 3

Avian Report.indd 3 7/24/18 6:2

ISBN-13: 978-1-938956-20-1 

ISBN-10: 1-938956-20-6 
Corresponding Authors

Michael T. Wells, PhD.

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5336

michael_wells@fws.gov

Authors’ Complete Contact Information

Jeffrey C. Gosse, PhD

Regional Energy Coordinator

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5138

jeff_gosse@fws.gov

Rebecca L. Horton

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5196

rebecca_horton@fws.gov

Kevin W. Heist, PhD.

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

Phone: 612/713 5196

Email: kevin_heist@fws.gov

Daniel C. Nolfi

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5195

daniel_nolfi@fws.gov

Erik C. Olson

Fish and Wildlife Biologist (GIS)

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5488

erik_olson@fws.gov

Nathan A. Rathbun

Fish and Wildlife Biologist

Ecological Services

5600 American Blvd. West, Suite 990

Bloomington, MN 55437

612/713 5182

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

Recommended citation: Wells, M.T., T. S. Bowden, 

K.W. Heist, R. L. Horton, D. C. Nolfi, E. C. Olson, 

Rathbun N. A., and J. C. Gosse. 2018. Great 

Lakes Avian Radar Technical Report Lake Huron 

Lakeshore: Alcona and Presque Isle, MI, Fall 2015 

and Spring 2016. U.S. Department of Interior, 

Fish and Wildlife Service, Biological Technical 

Publication FWS/BTP-XXXXX-2018

ISSN [Insert ISSSN#] Electronic ISSN [Insert 

Electronic ISSN#]

Biological Technical Publications online: 

http://digitalmedia.fws.gov/cdm/search/collection/

document/searchterm/Biological%20Technical%20

Publications/field/collec/mode/exact/conn/and/order/

nosort

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Table of Contents

List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

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

Objective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Study Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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

Data Collection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Data Processing And Quality Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Data Summary And Trends Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Trackplots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Directional Trends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Temporal Trends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Altitudinal Trends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Radar Study And Management Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Literature Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Appendices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

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i Great Lakes Avian Radar Technical Report Lake Huron Shoreline

List of Figures

Figure 1. Locations where MERLIN Avian Radar Systems were deployed during the fall 2015 

and spring 2016 migration seasons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 2. Land cover types found within a 3.7-km radius of the radar locations in Presque Isle Co. 

and Alcona Co. during fall 2015 and spring 2016. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

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

used in Michigan during fall 2015 and spring 2016. Graphic provided by DeTect, Inc.. . . . . . . . . . . . . . . . . . . 8

Figure 4. Vertical and horizontal clutter maps from Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . 10–11

Figure 5. Schematic of the vertical scanning radar and standard front. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 6. Graphical representation of the structural form of the vertical scanning radar 

within the standard front used for density estimates.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 7. Volume of 50-m altitude bands within the standard front as estimated with Monte Carlo integration. . . . . 16

Figure 8. Trackplots during 1-hour increments recorded by horizontal and vertical scanning 

radars during an apparent nighttime migration event in Presque Isle Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 9. Trackplots during 1-hour increments recorded by horizontal and vertical Scanning 

radars during an apparent nighttime migration event in Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 10. Target direction during four biological periods during fall 2015 and spring 2016 

at sites in Presque Isle Co. (left) and Alcona Co. (right).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 11. Hourly counts by horizontal and vertical radars from Aug. 3–Oct. 27, 2015 in Presque Isle Co... . . . . . . . . . 25

Figure 12. Hourly counts by vertical radars from Aug. 4-Oct.27, 2015 in Alcona Co... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 13. Box plots showing variability in target passage rate (targets/km/hr) during four biological 

periods for fall 2015 at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 14. Mean hourly target passage rate during fall 2015 at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . 28

Figure 15. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in Presque Isle Co. 

(top row) and Alcona Co. (bottom row) from August 7–October 23, 2015.... . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 16. Comparison of nocturnal and diurnal target passa8\9ge trends (based on a moving 7-day mean) 

during fall 2015 at sites in Presque Isle Co. and Alcona Co... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 17. Comparison of trends at Presque Isle Co. and Alcona Co. during night and day 

(based on a moving 7-day mean)....................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 18. Altitude profile of targets at sites in Presque Isle Co. by biological period. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 19. Altitude profile of targets at sites in Alcona Co. by biological period.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 20. A sample of hourly altitude profiles corrected for the shape of the sample volume in Presque Isle Co... . . 36

Figure 21. A sample of hourly altitude profiles corrected for the shape of the sample volume in Alcona Co. . . . . . . . . . 37

Figure 22. Altitude profile of target density below 400 meters at sites in Presque Isle Co.

and Alcona Co... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 23. Percentage of nights when the maximum density (targets/1,000,000 m3/altitude band) or count 

(targets/altitude band) occurred within an altitude band at sites in Presque Isle Co. and Alcona Co... . . 38-39

Figure 24. Percentage of night hours when the maximum density (targets/1,000,000 m3/ altitude band)

or count (targets/altitude band) occurred within an altitude band at sites in Presque Isle Co.

and Alcona Co. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

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Figure 25. Mean hourly target height (m) during fall at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . 40

Figure 26. Hourly variation in flight altitude based on target density (targets per million cubic m)

during fall 2015 in Presque Isle Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 27. Hourly variation in flight altitude based on target density (targets per million cubic m) 

during fall 2015 in Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 28. Predicted departure location of migrants based on average nightly flight paths.. . . . . . . . . . . . . . . . . . . . . . . 43

Figure 29. Trackplots during 1-hour increments recorded by horizontal and vertical scanning

radars during an apparent nighttime migration event in Presque Isle Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Figure 30. Trackplots during 1-hour increments recorded by horizontal and vertical Scanning

radars during an apparent nighttime migration event in Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 31. Target direction during four biological periods during fall 2015 and spring 2016 at sites in 

Presque Isle Co. (left) and Alcona Co. (right).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Figure 32. Hourly counts by horizontal and vertical radars from March 29–June 3, 2016 in Presque Isle Co.. . . . . . . . 52

Figure 33. Hourly counts by horizontal and vertical radars from March 29–June 3, 2016 in Alcona Co.. . . . . . . . . . . . . 54

Figure 34. Box plots showing variability in target passage rate (targets/km/hr) during four biological 

periods for spring 2016 at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Figure 35. Mean hourly target passage rate during spring 2016 at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . 56

Figure 36. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in Presque Isle Co. 

(top row) and Alcona Co. (bottom row) from April 1–June 10, 2016. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Figure 37. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during spring 2016 at sites in Presque Isle Co. and Alcona Co... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Figure 38. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during spring 2016 at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Figure 39. Altitude profile of targets during the four biological periods at Presque Isle Co.. . . . . . . . . . . . . . . . . . . . . . . 62

Figure 40. Altitude profile of targets during the four biological periods at Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Figure 41. A sample of hourly altitude profiles corrected for the shape of the sample volume 

in Presque Isle Co. (top) and Alcona Co. (bottom).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Figure 42. A sample of hourly altitude profiles corrected for the shape of the sample volume 

in Presque Isle Co. (top) and Alcona Co. (bottom). .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Figure 43. Altitude profile of target density below 400 meters at sites in Presque Isle Co. and Alcona Co. . . . . . . . . . . 68

Figure 44. Percentage of nights when the maximum density (targets/1,000,000 m3/altitude band) or count 

(targets/altitude band) occurred within an altitude band at sites in Presque Isle Co. and Alcona Co.. . . . . 69

Figure 45. Percentage of night hours when the maximum density (targets/1,000,000 m3/ altitude band) or count 

(targets/altitude band) occurred within an altitude band at sites in Presque Isle Co. and Alcona Co... . . . . 69

Figure 46. Mean hourly target height (m) during spring at sites in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . 70

Figure 47. Hourly variation in flight altitude based on target density (targets per million cubic m) 

during spring 2016 in Presque Isle Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Figure 48. Hourly variation in flight altitude based on target density (targets per million cubic m) 

during spring 2016 in Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Figure 49. Predicted departure location of migrants based on average nightly flight paths at Presque Isle.. . . . . . . . . 73

Figure 50. Predicted departure location of migrants based on average nightly flight paths at Alcona.. . . . . . . . . . . . . . 74

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

vs. a continuous sampling schedule (bottom graphic).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

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

Presque Isle Co. and Alcona Co. during fall 2015 and spring 2016.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Table 2. Survey effort (hrs) by vertical and horizontal scanning radars during fall 2015 and spring 2016 

in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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

(r ≥ 0.5) of targets during biological time periods in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . 23

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

Presque Isle Co. and Alcona Co. during fall 2015.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 5. Comparison of mean target passage rate (TPR) and mean height (m) with standard deviations 

during four biological time periods in Presque Isle Co. and Alcona fall Co. 2015. . . . . . . . . . . . . . . . . . . . . . . 32

Table 6. Survey effort (hrs) by vertical and horizontal scanning radars during spring 2016 in 

Presque Isle Co. and Alcona Co... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

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

(r ≥ 0.5) of targets during biological time periods in Presque Isle Co. and Alcona Co.. . . . . . . . . . . . . . . . . . . 51

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

in Presque Isle Co. and Alcona Co. during spring 2016.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Table 9. Comparison of mean target passage rate (TPR) and mean height (m) with standard deviations 

during four biological time periods in Presque Isle Co. and Alcona Co. spring 2016. . . . . . . . . . . . . . . . . . . . 61

List of Tables

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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 Anna Peterson (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 also 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 Michigan Field Office. This 

manuscript benefited from four external reviews 

and we thank those that contributed, which included 

Jennifer Wong and Scott Hicks, both of the USFWS

East Lansing, Michigan Field Office.

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v Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Executive Summary

density of targets at low altitudes may present 

conservation concerns. The data we collected 

showed the ebb and flow of migration across the 

sampling period and document that nocturnal peaks 

continued through early June for the spring and late 

October for the fall. Given the amount of time that 

migration occurred in the sampled sites, it seems 

that curtailing wind energy operations to minimize 

bird and bat mortality during nocturnal pulses could 

result in limited operational time along the shoreline 

during the migration season. Combining the 

results of radar studies and fatality searches would 

greatly improve risk assessments and assist with 

interpretation of standardized radar studies.

Avian radar is often relied upon to perform 

surveys for pre-construction risk analysis. While 

an important tool, few regulatory agencies 

have experience implementing avian radar or 

otherwise recognize the strengths and limitations 

of the technology. This report highlights some 

considerations about avian radar and reviews 

some potentially confusing metrics. In addition 

to providing information relevant to wildlife 

conservation in the Great Lakes region, the concepts 

we present in this report are widely relevant to 

reviews of avian radar studies and provide methods 

that identify components of migration such as:

■ Nocturnal pulses

■ Season length

■ Estimated density per altitude band

■ 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. Our use of commercialgrade avian radar to document migration is a broadscale effort toward that end. To our knowledge, this 

effort represents the first of its kind by the U.S. 

Fish and Wildlife Service.

Global wind patterns help to move millions of 

migrating birds and bats through the Great 

Lakes region where shorelines provide important 

stopover habitat. Shorelines are thought to 

concentrate migrants as they offer the last refuge 

near a geographic obstacle and are likely used for 

navigation. Shorelines also offer areas attractive for 

wind energy development, which are known to cause 

mortality of birds and bats. 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 activity 

patterns, timing, and duration of migration that 

occurred along shorelines of the Great Lakes.

We placed avian radar systems on the Western 

shore of Lake Huron where the automated 

systems tracked and recorded target (bird and bat) 

movements continuously from early August to late 

October, 2015, and from late March to Mid-June 

2016. 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 appeared strong along the western 

Lake Huron shoreline at both study sites. Mean 

nocturnal passage rates were greater than mean 

passage rates for dawn, day, and dusk combined 

at both of our locations. Nocturnal movement was 

typically oriented in a northerly direction; however, 

we also recorded other behaviors associated with 

migrants such as reverse migration, dawn ascent, 

and migrants over water returning to land at dawn. 

After correction, peak density occurred between 

50—150 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 to identify areas 

where impacts to wildlife could be minimized. We 

documented migration activity in the air space 

above our study areas, which indicates that the 

Avian Report.indd 10 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 1

Introduction

migration. For bats, available studies suggest 

migrants varied their choice to circumnavigate 

above shorelines or cross lakes and some longdistance migrants used torpor to postpone migration 

during periods of unfavorable conditions (McGuire 

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

as the necessity of using stopover habitat during 

migration likely contribute to the increased use of 

shorelines and emphasize the importance of these 

areas for conservation.

Migrants concentrated along shorelines can be 

very mobile. In addition to immediate refueling 

and rest, migrants make broad scale flights among 

habitat patches, explore wind conditions, and orient 

for migration. For example, radio tagged bird 

and bat migrants on the north shore of Lake Erie 

made repeated movements among habitat patches. 

Individuals relocated as far as 18 and 30 km from 

their capture site (maximum distance tracked for a 

bat and bird species, respectively) prior to resuming 

migration (Taylor et al. 2011). Nocturnal migrants 

such as warblers and other neotropical birds 

regularly engage in morning flights along shorelines 

(Wiedner et al. 1992). These flights typically 

occur within 2 hours of sunrise and are thought to 

represent reorientation along a geographic obstacle 

or movements among stopover habitats (Able 1977, 

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

this nature often occur above tree line (Bingman 

1980) but lower than heights 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). These flights are thought to represent 

normal activity of migrant birds and possibly bats 

as they calibrate their internal compass and test 

wind speed and direction aloft. In addition to these 

activities while in stopover, migration flights follow 

north-south oriented shorelines en route to their 

destination (Buler and Dawson 2012) while east-west 

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). Cumulatively, these types of activities define 

a use area near lake shores that include a variety 

of movements and altitudes for landscape level, 

exploratory, and migratory flights. These activities 

may increase vulnerability to collision risk with tall 

structures such as buildings, communication towers, 

or wind turbines.

The Great Lakes support one of the largest bodies of 

freshwater on the planet and collectively represent 

a surface area of nearly 245,000 km2

 with over 

17,500 km of shoreline. Global wind patterns help to 

move millions of migrating birds through the Great 

Lakes region (Rich et al. 2004, Liechti 2006, France 

et al. 2012) and lake shorelines feature widely 

recognized Important Bird Areas (Audubon 2013). 

Bat migration is less studied but findings suggest 

similar patterns of wind use (Dechmann et al. 2017). 

Migrants passing through the region concentrate 

near shorelines (Dzal et al. 2009, Ewert et al. 

2011, Peterson and Niemi 2011, Buler and Dawson 

2012, France et al. 2012), which provide important 

stopover habitats—en route areas used temporarily 

for refueling, rest, and protection. These shorelines 

offer increased foraging opportunities relative to 

inland areas (Smith et al. 2004, 2007; Bonter et 

al. 2007, 2009) and may be used as a visual cue for 

navigation or for refuge prior to or after crossing 

open water (Buler and Moore 2011).

Given their location and size, the Great Lakes likely 

represent a geographic obstacle that migrants 

choose to cross, or not, based on environmental and 

physiological conditions at the time of encounter 

(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 long 

flight due to the cost of carrying high fuel loads 

(Alerstam 1990). This is perhaps one reason why 

migrants partially circumnavigate the Great Lakes, 

which they have the physiological capability of 

crossing (Alerstam 1990, 2001; Ruth 2007). 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) that are associated with migration (McGuire 

et al. 2012a, 2012b). In this trade-off, shorelines 

offer refuge when conditions do not favor flights 

over water.

Migrants challenged by an obstacle 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 NaefDaenzer (2011) found that birds with low fuel loads 

and/or facing unfavorable weather conditions 

returned to shoreline habitat rather than continue 

across open water in a direction appropriate for 

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2 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Utility-grade wind facilities have been associated 

with mortality events for migrating vertebrates 

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

Thelander 2008), and chronic fatalities across the 

U.S., particularly for bats, are a concern (Timm 

1989, Johnson 2005, Arnett and Baerwald 2013, 

Hayes 2013, Smallwood 2013). For example, three 

species of long-distance migratory bats that are 

impacted by wind energy facilities account for 

approximately 75% of all bat mortalities (Kunz et al. 

2007a, Cryan 2011, Arnett and Baerwald 2013). 

These migrants, the hoary bat (Lasiurus cinereus), 

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

make up 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 but also found that 

little brown bat (Myotis lucifugus) and big brown 

bat (Eptesicus fuscus) fatalities were substantial 

(Gruver et al. 2009, BHE Environmental 2010, 

Grodsky et al. 2012).

Low reproductive rates inhibit the ability of bats 

to rebound from population decline (and Entwistle 

2000), and these declines have already begun for 

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

and have contributed to the Federal listing of the 

northern long-eared bat (Myotis septentrionalis) as 

a threatened species under the Endangered Species 

Act. Cumulative impacts on migrant bird and bat 

species are a concern, and this concern will increase 

with the growth of wind energy if methods to avoid 

or minimize mortality events are not established 

(Frick et al. 2017). Some promising conservation 

measures have been proposed to reduce mortality 

levels, such as reduced cut-in speeds; however, the 

greatest benefit to the conservation of migrants may 

lie in our ability to identify and avoid future growth 

in locations where migrants concentrate.

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 to migratory populations 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 that may limit habitat availability 

and/or reduce habitat quality (France et al. 2012). 

Furthermore, White-nose Syndrome is devastating 

hibernating bat populations and has increased the 

need to identify conservation areas as several of 

these species face the risk of extirpation in the Great 

Lakes region (Turner et al. 2011). In response to 

factors such as these, substantial efforts are being 

made to identify and protect stopover habitat along 

the Great Lakes shorelines (Buler and Dawson 2012, 

Ewert et al. 2012, France et al. 2012, Johnson, 2013). 

With climate change considerations calling for both 

an increase in renewable energy development and 

conservation of migratory species, careful planning 

is needed to balance these demands.

There is a national movement towards a 20% wind 

energy sector in the U.S. market by 2030 (U.S. 

DOE 2008). Wind energy installation is currently 

on target towards achieving this goal (U.S. EIA 

2017). If achieved, this would represent a nearly 

five-fold increase in wind energy capacity during 

the next 15 years (Loss et al. 2013). Additionally, the 

U.S. Department of Energy (2015) has conducted 

a study showing that 35% of the energy demands 

of the U.S. could be met by wind energy in 2050. 

Explorations have also been conducted by the 

National Renewable Energy Laboratory that 

conclude that over 400 GW of electricity could be 

produced by wind power in 2050, up from 60 GW in 

2012 (Mai et. al 2012, Loss et al. 2013). Coinciding 

with this national effort, wind energy developments 

are increasing within the Great Lakes region, where 

windy shorelines near population centers offer 

attractive areas for turbine placement (Mageau et 

al. 2008, Great Lakes Commission 2011).

Avian Report.indd 12 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 3

To help meet the needs of both renewable energy 

development and wildlife conservation, we 

established this project to identify the activity 

patterns, timing, and magnitude of migration 

occurring along shorelines of the Great Lakes. 

Because bats and many bird species migrate during 

the nighttime hours throughout the spring and 

fall, documenting the migration of these animals 

is challenging due to the difficulty of observing 

nocturnal movements that occur sporadically 

throughout the season. To address this challenge, 

we used two avian radar units that operated 

24 hours per day, and each unit simultaneously 

scanned horizontal and vertical planes. We chose 

radar because of these and other benefits and 

to provide an alternative metric to our acoustic 

monitoring program, which has different strengths 

and weaknesses (Horton et al. 2015). 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 (Bonter 

et al. 2009), indicating that migrants using the 

airspace are also using stopover habitat in the area. 

Our objectives for the portion of the study we are 

reporting on included the following:

■ Monitor locations along shorelines of Lake Huron 

using consistent methodology.

■ Maintain an archive of continuously recorded 

radar data during the fall and spring migration 

seasons.

■ Identify activity patterns captured by radar that 

are diagnostic of migration.

■ Estimate the duration of the migration season.

■ Document changes in the behavior of migrants 

under varying environmental conditions and during 

different parts of the season.

■ Document changes in behavior between fall and 

spring migration seasons.

Avian Report.indd 13 7/24/18 6:2
4 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Methods

Selection of radar monitoring sites was achieved 

through a combination of geographic modeling and 

on-site assessment to locate areas near shorelines 

with unimpeded views. First, large sections of 

Great Lakes shorelines were identified as potential 

study areas for the migration season. Esri ArcGIS 

software was used to model the areas of interest 

to find locations that could be suitable for radar 

siting. This suitability modeling incorporated 

datasets describing elevation, land cover, and 

shorelines of the Great Lakes. Additional landscape 

characteristics were derived from these datasets 

(elevation below local maximum elevation, percent 

forested, distance to forest, distance from shoreline, 

etc.) and ranked to create a continuous raster 

surface within the area of interest with estimated 

suitability values. Contiguous areas with high 

suitability identified through the GIS modeling 

process were targeted for on-site assessment.

Biologists were dispatched to areas of interest to 

do a more thorough assessment of potential sites 

identified by the modeling effort. This assessment 

included evaluating the land use, line of sight to 

shorelines, and accessibility 

for placement of radar units. 

Additional locations not 

identified through the modeling 

were frequently discovered 

through this process and 

evaluated as well. When a 

location was determined by field 

biologists to be highly suitable 

relative to the other locations 

visited in the field, contact was 

initiated with property owners 

to obtain permission to set up 

the radar units.

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 

Study Area and Site Selection

During the fall 2015 season, we selected two sites 

along Lake Huron for radar placement; one site was 

towards the northwest end of the lake in Michigan 

(Figure 1). We located sites within 1.5 km from the 

Lake Huron shoreline to monitor airspace above 

inland, shoreline and lake areas. The northern 

site, located in Presque Isle County, Michigan at 

45.396318° N, -83.720929° W was approximately 

1.5 km from the shoreline and 171 m above sea 

level. Here, the radar unit was placed in a hayfield 

in an area where wetlands and forest were the 

predominant land cover types within range of the 

radar unit according to our analysis using Esri 

ArcGIS software and the 2006 National Land 

Cover Database (Fry et al. 2011) (Table 1, Figure 2, 

Appendix 2). The southern site, located in Alcona 

County, Michigan at 44.67620° N, -83.29481° W was 

approximately 1.0 km from the shoreline and 285 

m above sea level. This radar was also placed in a 

hayfield in an area where forest was the primary 

land cover type within range of the radar unit 

(Table 1, Figure 2, Appendix 2).

Figure 1. Locations where MERLIN Avian Radar Systems were 

deployed during the fall 2015/spring 2016 migration seasons. Map 

image is the intellectual property of Esri and is used herein under 

license. Copyright© 2014 Esri and its licensors. All rights reserved.

Avian Report.indd 14 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 5

Figure 2. Land cover types found within a 3.7 km radius of the radar units located in Presque Isle and 

Alcona Counties during fall of 2015 and spring of 2106. Map image 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 radar locations located in 

Presque Isle and Alcona Counties during the fall of 2015 and spring of 2016.

National Land Cover Class Presque Island County Alcona County

Open Water 35.42% 33.79%

Developed1 4.48% 7.76%

Barren Land 10.22% 1.60%

Forest2 19.81% 36.12%

Grassland/Shrubland 7.08% 4.33%

Planted/Cultivated3 0.12% 4.27%

Wetlands4 22.87% 12.12%

1 Includes low, medium, and high intensity developed land and developed open space 

2 Includes deciduous, evergreen, and mixed forest 

3 Includes pasture/hay and cultivated crops 

4 Includes woody wetlands and emergent herbaceous wetlands

Avian Report.indd 15 7/24/18 6:2
6 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

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 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. Weather data were summarized and 

stored every 5 minutes. The anemometer was 

attached to the radar unit and measured wind 

speed at a height of about 6 m above ground level.

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—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, 2.92–

3.08 GHz frequency range, and were configured 

to operate with both short and medium pulse 

(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, which 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 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 

spin perpendicular to each other at a rate of 20 

revolutions per minute and were synchronized so 

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

radars used by the U.S. Fish and Wildlife Service during the fall 2015 and spring 2016. Graphic provided 

by DeTect, Inc.

Avian Report.indd 16 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 7

Biologists returned to the site periodically during 

the data collection period to ensure continuous 

function, monitor raw (unprocessed analog radar 

returns) and processed radar outputs, provide 

routine maintenance (such as re-fueling and oil 

changes), and manage data storage. In addition to 

processed data, we maintained all raw radar data for 

potential reprocessing until the end of the season.

Radar System Outputs

The MERLIN software generates more than 

30 measurements to describe target size, shape, 

location, speed, and direction of movement. These 

data are 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 

less 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, 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 it agreed with 

the raw radar display. We later viewed 15-minute 

and 1-hour Trackplots to assess target direction and 

height both on site and remotely on a regular basis 

during the season.

Data Processing and Quality Control

Prior to data analysis, data processed by MERLIN 

software were further evaluated for potential 

contamination by non-targets. While an automated 

rain filter was used, during some time periods it did 

not remove all rain from the recorded outputs. In 

addition, insects and other forms of transient clutter 

may be recorded during data collection. Biologists 

reviewed all data in 15-minute time increments and 

removed time periods that were dominated by rain; 

data were also reviewed for time periods dominated 

by insects or other forms of transient clutter; 

however, there were no time periods where these 

types of non-desirable targets needed to be removed 

from the dataset. We relied on visual inspection of 

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 when present. Unknown contamination 

that mimicked patterns of desired targets was not 

removed from the database and, to the extent that 

this occurred, contributed to error associated with 

indices. In addition, we evaluated initial counts by 

generating a time series to show the variation in the 

number of targets per hour across the season for 

both HSR and VSR radars. In general, the HSR 

and VSR hourly counts are positively correlated, 

with the HSR having higher counts due to a 

larger sampled area. In situations where the VSR 

Radar Set Up and Data Collection

Radar systems were deployed during the fall season 

from the first week of August to the last week of 

October of 2015. We continued our study for the 

spring season from the last week of March to the 

second week of June.

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 north-south axis of migration along the 

shoreline of Lake Huron during the fall and spring 

seasons, and oriented vertical scanning radars to 

an angle that was slightly off of perpendicular to 

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 microsite selection. Micro-site selection is important in 

that positioning the radar can affect the amount of 

interference from ground clutter or other sources of 

radar interference. If large areas were obstructed 

from the radar view or if substantial amounts of 

clutter impeded data collection, 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 data collection, clutter maps were 

generated using 60-scan composite images (Figure 

4) at time periods with low biological activity in 

order to identify areas with constant returns (areas 

that are white) 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 

and, as a result, also reduced our ability to detect 

targets in these areas.

Following this initial set up, MERLIN software was 

fitted to site conditions. The MERLIN software 

provides real-time processing of raw radar data to 

locate and track targets while excluding non-targets 

and rain events. However, parameters used by the 

tracking software require adjustments to account 

for site-specific conditions. DeTect personnel trained 

our biologists in establishing these 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.

Avian Report.indd 17 7/24/18 6:2
8 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 4a. Clutter maps from vertical (left) and 

horizontal (right) scanning radars at study sites 

in Presque Isle and Alcona Counties during 

the fall of 2015 migration season. Due to loss of 

motor and gearbox, the horizontal radar was 

not present at the Alcona County site. Brighter 

areas represent static returns from stationary 

objects such as tree lines and fencerows. Detection 

of targets may be lost in these areas due to 

obstruction from these objects.

Presque Isle County, MI Fall 2015 Cluster Maps

Alcona County, MI Fall 2015 Cluster Maps

Avian Report.indd 18 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 9

Figure 4b. Clutter maps from vertical (left) and horizontal (right) scanning radars at study sites in 

Presque Isle and Alcona Counties during the spring of 2016 migration season.

Presque Isle County, MI Spring 2016 Cluster Maps

Alcona County, MI Spring 2016 Cluster Maps

Avian Report.indd 19 7/24/18 6:2
10 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

target 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 and this metric 

is also reported 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 5).

resulted in higher counts than the HSR or where 

peak counts appeared to be outliers, the data were 

further investigated for evidence of contamination 

or potential issues with radar performance. On 

rare occasions when time periods with anomalies 

appeared to represent artifacts not related to 

target movement (e.g., rain events, insects or data 

processing errors) they were removed from further 

analysis.

Once contaminated time periods were removed, 

we summarized data using SQL queries provided 

with the MERLIN radar system. Data from the 

HSR were used to calculate hourly counts and 

Figure 5. This schematic depicts the vertical scanning radar beam from two different views and pictures of 

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

The standard front 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 bottom graphic the radar rotation is suspended so that the beam emits directly 

upward; this view is an approximation of the beam dispersion as it travels away from the radar unit 

(schematic not drawn to scale).

Avian Report.indd 20 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 11

Biological Time Periods

For each site location, sunrise and sunset times 

were calculated and target counts were further 

segregated into four biological time periods: dawn, 

day, dusk, and night; with dawn representing 30 

minutes before sunrise to 30 minutes after sunrise, 

day representing 30 minutes after sunrise to 

30 minutes before sunset, dusk representing 

30 minutes before to sunset to 30 minutes after 

sunset, and night representing 30 minutes after 

sunset to 30 minutes before sunrise.

Data Summary and Trends Analysis

We used the processed data to assess activity 

patterns that are associated with migration. 

Horizontal Trackplots were viewed to identify 

changes in activity and to investigate migrant 

behaviors such as reverse migration (Akesson 1999) 

and migrants moving toward shore at dawn; vertical 

Trackplots were viewed to investigate changes in 

activity such as dawn ascent (Myres 1964, Diehl 

et al. 2003). We used target counts as an index of 

abundance to identify directional, temporal, and 

altitudinal trends.

Directional Trends—Mean angle and concentration 

(r) of target directions were analyzed following 

methodology for circular statistics (Zar 1999) 

provided within DeTect SQL queries. The angular 

concentration value has a value of 1 when all angles 

are the same and a value of 0 when all angles cancel 

each other (e.g., if 50% of the vectors are 180° 

and 50% are 360°, then there is not a predominate 

direction because there were as many targets 

heading south as there were heading north and thus 

the angular concentration is 0), indicating that there 

is no predominant direction of travel. We anticipated 

a generally southwards direction of movement 

from nocturnal targets during the fall migration 

season, and northwards direction in spring. We 

report the mean direction of nocturnal targets and 

the percent of nights targets traveled in a direction 

between northwest or southwest and northeast or 

southeast for spring (315°—45°) and fall (135°—

225°), respectively. We used radial graphs to plot 

the number of targets per 8-cardinal directions (i.e., 

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

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

day, dusk, night).

Temporal Trends—We plotted counts of targets 

per hour processed by MERLIN software for both 

HSR and VSR antennas as a time series to identify 

pulses of nocturnal activity, season duration, and 

changes in patterns of activity over time. The HSR 

and VSR radars have different strengths that 

complement one another; these indices were plotted 

together. The HSR index tracks low-flying targets 

in a 360 ̊ span around the radar unit and detection 

is not affected by the target’s direction of travel as 

with the VSR. However, this index is much more 

affected by ground clutter than the VSR, which 

affects target detection and tracking. Errors caused 

by ground clutter lead to both under- and overcounting; targets blocked by ground clutter may not 

get counted, and targets that fly in and out of areas 

with ground clutter may get counted multiple times. 

This leads to HSR counts that are more influenced 

by site conditions than VSR counts. However, the 

HSR index better captures targets under certain 

conditions, such as when targets are primarily at low 

elevation and/or traveling parallel to the VSR. The 

HSR is also much more susceptible than the VSR to 

beam bending from dynamic atmospheric conditions; 

beam refraction in the VSR is minimal primarily due 

to its orientation. The VSR index was used to track 

targets captured within the standard front and has 

more consistent detection than HSR as it mostly 

tracks against clear air, except in the lowest altitude 

bands. Its detection is affected by target direction 

and distance from the radar (Bruderer 1997, 

Schmaljohann et al. 2008). The VSR is also impacted 

by ground clutter. Plotting these indices together 

provided a more comprehensive understanding of 

changes in target activity over time.

We used the VSR index to calculate target passage 

rate (TPR). We calculated TPR as the number of 

targets per standard front per hour using DeTect 

SQL queries. Hours with less than 30 minutes of 

recording time were omitted from this calculation. 

For example, after removing all hours with less 

than 30 minutes of clean data, nocturnal TPR for a 

given night (biological time period) was calculated 

by dividing the target count by the number of 

nighttime minutes and multiplying by 60 to provide 

the number of targets per hour during that night. 

We extended this metric to the season and calculated 

mean TPR for biological time periods and hours of 

the season. Mean nocturnal TPR for the season is 

the sum of night TPRs divided by the number of 

nights sampled. Similarly, mean hourly TPR for 

the season is the sum of TPRs for an hour period 

divided by the number times that hour was sampled. 

We also calculated mean nocturnal (night biological 

period) and diurnal (day biological period) TPR 

for weeks during the sampling period. These were 

calculated in two ways. To show the variability 

among 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. To better illustrate nocturnal and diurnal 

trends in TPR across the season, we plotted 7-day 

moving means of TPR as line graphs.

Altitudinal Trends—DeTect SQL queries calculated 

height estimates from the VSR data of targets 

tracked within the standard front. 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 ground level as 

measured at the radar unit; this measurement does 

not take into account changes in topography as you 

move across the landscape. Both sites were in areas 

with generally flat topography, and little distortion 

due to topography was expected. We used these 

estimates to calculate mean altitude of targets above 

ground level by biological time period and hour and 

report mean and median altitudes for the season.

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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 saturated this space 

with 10 million random points. For the radar beam, 

we determined two simple rules that defi ned 

whether a point was in the survey volume. The fi rst 

rule was that the distance of the randomly drawn 

point from the origin was 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 6) was less than 12.5o (i.e., half the angle of 

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

beam as estimated via Monte Carlo integration was 

within 0.5% of the analytical solution using spherical 

coordinates; thus, the number of random points 

that we used provided a reasonable approximation 

of the volume. With the volume of a full sweep of 

the radar beam described, we were able to further 

constrain the Monte Carlo integration to describe 

the structural volume of the radar beam within a 

standard front (Figure 6) and within altitude bands 

(Figure 7).

The number of targets per altitude band is often 

reported by other researchers; however, a volume 

correction is not often reported. We wanted 

to compare our correction to the uncorrected 

method; however, count data and volume data are 

on different scales. For this reason, we compare 

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).

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 fi rst estimated the volume of the radar beam’s 

approximate geometric shape. The width of the 

radar beam expands as it travels from the radar 

resulting in increased survey volume with distance 

from origin. The shape of the survey volume 

contains the space in which targets have the 

potential of being detected and represents one of 

several considerations that defi ne 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 density of 

targets (targets per 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 data during the biological time period of 

interest and multiplying by 60.

To estimate the volume of 50-m altitude bands that 

are constrained by the standard front we used 

Monte Carlo integration (Press et al. 2007). The 

volume contained by the shape of the radar beam 

can be calculated using spherical coordinates and 

multiple integration. However, subjecting this 

volume to Cartesian constraints (i.e., the standard 

front and altitude bands) complicates the calculation 

and the volume bands are more easily estimated 

using Monte Carlo integration. Monte Carlo 

integration is a method 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. 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, as the number of random points 

approaches infi nity, the estimation approaches truth 

(an exact calculation).

Figure 6. 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 are not 

included in the volume of the radar beam.

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Figure 7. 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 200 m.

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Results-Fall 2015

During the fall 2015 season, we began data collection 

August 3 and 4 at the Presque Isle and Alcona 

County sites, respectively. Data collection ended on 

October 27, 2015 at both sites, resulting in a survey 

period of 2042 hours at Presque Isle County and 

Alcona County sites (Table 2). Data were recorded 

continuously while the radar units were operational. 

Gaps in analyzed data occurred during rain events 

and when the radar units were not operational due 

to maintenance or malfunction (radar downtime). 

The motor and gearbox for the HSR were lost at the 

beginning of the season for the Alcona County site, 

and due to lack of available parts, could not be fixed 

during the fall 2015 season; subsequently, no HSR 

data was collected at this site. When correcting for 

radar downtime and removal of periods with rain, 

the radars collected useable data 85.5% and 70.3% 

of the season in Presque Isle County for vertical 

and horizontal radars, respectively, and 88.6% of 

the fall season for vertical radars in Alcona County. 

As mentioned above, no data were collected for the 

Alcona County HSR. There we no usable data from 

horizontal radar in Alcona County, MI.

Qualitative Assessments

Plots of tracked targets showed images of nocturnal 

migration events at both locations (Figure 8 and 

9). For example, on October 9 at the Presque 

Isle County site (Figure 8), the horizontal radar 

recorded scattered activity and low numbers from 

12:00-18:00. During the 18:00 hour, there was an 

increase in southward movement recorded on the 

horizontal radar, but still relatively few targets 

are recorded on the vertical radar at a relatively 

low altitude. During the 20:00 hour, most targets 

were oriented in a southern direction, and vertical 

radar recorded significantly more targets with 

a greater range of altitudes being used. Targets 

continued south during the 23:00 hour, with some 

shifts to the southeast and southwest. Vertical radar 

continued to record large numbers of targets and 

a wide range of heights at this time. By 04:00 on 

October 10, target directions began to scatter in 

multiple directions and continued to 05:00, possibly 

as migrants began to search for suitable stopover 

habitat near dawn. Vertical radar recorded a decline 

in activity in the 04:00 and 05:00 hours compared 

with the peak of the last several hours. By 12:00, the 

activity had returned to the low activity levels seen 

the previous day from 12:00-18:00. The patterns 

here (directionality changes, changes in height 

and density of targets) are indicative of a pulse of 

migration activity.

While the Alcona County site did not record 

horizontal data, the vertical radar also showed a 

pattern of migratory activity. From 12:00-18:00 on 

October 13, there were few targets moving, and they 

were generally low in altitude. During the 18:00 

hour, the number of targets rose, and increased in 

height. Further increases in number and altitude 

use continued at 20:00, with airspace below 750 

m saturated with targets and with considerable 

numbers up to 2000 m. Migratory activity peaked 

between 23:00 and 01:00 on October 14, with heavy 

use of airspace up to 1500 m and continued common 

use up to 2000 m. Numbers of targets declined 

during the pre-dawn and dawn hours of 04:00-0:600, 

but continued to use wide altitude bands. By 12:00, 

the densities returned to the same levels as the 

previous daytime, generally following the pattern 

of the Presque Isle County site and indicative of a 

migratory pulse.

Table 2. Survey effort (hours) by vertical and horizontal scanning radars during fall 2015 at our radar sites 

in Presque Isle and Alcona Counties.

Site Radar Survey Radar Time Radar Radar Data Usable % Usable

 Period Downtime1 Collected Data w/Rain Radar Data Data

Presque Isle VSR 2042 160 1882 135 1747 86%

Presque Isle HSR 2042 199 1843 407 1435 70%

Alcona VSR 2042 87 1955 147 1808 89%

Alcona HSR2 2042 2042 0 0 0 0%

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

2 The Horizontal radar malfunctioned and did not collect data for the survey period.

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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 4), resulting in 

reduced detection in the air space that was within 

the range of data collection (e.g., ~500 m altitude 

Figure 8. Images of tracks during 1-hour increments recorded by horizontal and vertical scanning radars 

during a migration event at our radar site in Presque Isle County. Horizontal radar images (columns 1 

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

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

October 9, 12:00

October 9, 20:00

October 10, 01:00

October 10, 05:00

October 9, 18:00

October 9, 23:00

October 10, 04:00

October 10, 12:00

on the right side of the Alcona County VSR (Figure 

9). 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 

(October 9, 23:00) and vertical (October 9, 23:00) 

Trackplots (seen at a range of about 1,400—2,000 m).

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Figure 9. Images of tracks during 1-hour increments recorded by vertical scanning radar during a 

migration event at our radar site in Alcona County, MI. Vertical radar images show target heights. 

Due to malfunction of the radar motor, horizontal radar was not functional.

October 13, 12:00 October 13, 18:00

October 14, 01:00 October 14, 04:00

October 13, 20:00 October 13, 23:00

October 14, 06:00 October 14, 12:00

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Directional Trends

During the fall 2015 season, nocturnal target 

direction was generally south at the Presque Isle 

County site (Figure 10). At the Presque Isle County 

site, mean nocturnal direction was 174° with an 

angular concentration (r) of 0.60 (n = 2,344,277 

targets), and during 65% of nights, mean target 

direction was between southwest and southeast 

(112.5°—247.5°). Onshore movement to the west at 

dawn was visible (Figure 10). Mean nightly direction 

at Presque Isle County came from all directions, but 

included vectors over substantial stretches of open 

water (Figure 28).

Temporal Trends

Time Series Plots—Hourly target counts provided 

by horizontal and vertical radars showed pulses of 

elevated nocturnal activity with peaks occurring 

a few hours before midnight at our study sites. 

Across our sampling period, these events were 

often clustered into groups of several nights and 

were first observed on September 1 and September 

19 at the Presque Isle County and Alcona County 

sites, respectively (Figures 11 and 12). At both sites, 

the occurrence and magnitude of nocturnal pulses 

continued through the season’s end.

Figure 10. Target direction per hour during four 

biological periods during fall 2015 at our sites in 

Presque Isle County, MI. Due to the malfunction of 

the horizontal radar, we could not present data from 

our Alcona County, MI site.

Presque Isle County, Mi Target Direction per Hour 

During Four Biological Time Periods Fall 2015

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

directionality (r ≥ 0.5) of targets during biological time periods at our sites in Presque Isle County 

during the fall 2015 season. 

Presque Isle 

Biological Period Mean Direction (degrees) r % time r ≥ 0.5 n

Dawn 217 0.24 56.9% 118975

Day 208 0.10 23.1% 449342

Dusk 8 0.21 38.5% 47509

Night 184 0.41 78.8% 2344277

The HSR of Alcona County was nonfunctional during the fall 2015 season.

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continues until the end of the recorded season in late 

October, indicating a continued migration through 

the end of the month and potentially beyond. Also 

apparent are differences in detection capability of 

the vertical and horizontal scanning radars. For 

instance, the shift to south-oriented targets at 18:00 

on October 9 is not detected by the vertical radar 

(Figure 8).

Different patterns of activity are apparent as the 

season progresses at our study sites. For example, 

beginning in early September activity patterns 

become dominated by nocturnal pulses that are seen 

on both horizontal and vertical radars in Presque 

Isle County; this pattern is apparent on the vertical 

radar for Alcona County as well (the horizontal 

radar malfunctioned during this season at our unit 

in Alcona County; Figures 11, 12). This pattern 

Hourly Counts by Horizontal and Vertical Radars: Presque Isle County, MI, Fall 2015

Figure 11. Hourly counts by horizontal and vertical radars from August 3–October 27, 2015 at the 

Presque Isle County site, MI. Light gray vertical lines represent midnight.

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Hourly Counts by Horizontal and Vertical Radars: Alcona County, Mi, Fall 2015

Figure 12. Hourly counts by vertical radar from Alcona County, MI in fall 2015. Light gray vertical 

lines represent midnight. Note differing scale from Figure 11.

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20 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

(approximately dusk through an hour after sunset). 

Peak timing differed by site, with the more northern 

Presque Isle County site having a peak near 

22:00-23:00, and the Southern Alcona County site 

at 21:00-22:00. This difference is likely due to 

migrants needing to cross open water to reach the 

northern site, as discussed below. At both locations, 

mean TPR gradually decreased as the night 

progressed, with the most drastic decline occurring 

around 06:00 and 07:00, which roughly corresponds 

with dawn (Figure 14).

Target Passage Rate—The pattern of mean TPR 

among the four biological time periods was similar 

between the two study sites (Figure 13) with mean 

TPR at night being greater than the combined 

means of the other three biological time periods 

(Table 4). Mean nocturnal TPR was 343± 428 SD 

(n = 84 nights) and 434 ± 430 SD (n=85 nights) at 

the Presque Isle County and Alcona County sites, 

respectively. Mean TPR varied by hour with peak 

numbers reached during the 20:00 and 23:00 hours 

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

Presque Isle County and Alcona County during fall 2015.

Biological Period Calcite Mean TPR Medor Rd. Mean TPR

Dawn 64 ± 82 86 ± 114

Day 18 ± 25 18 ± 20

Dusk 32 ± 41 37 ± 44

Night 343 ± 428 434 ± 430

Figure 13. Box plots showing variability in target passage rate (targets/km/hr) during four biological 

periods for fall 2015 in Presque Isle County and Alcona County. Whiskers represent the 1st and 4th

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

and blue diamonds represent seasonal mean for the time.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 21

Figure 14. Mean hourly target passage rate (targets/km/hr) during fall, 2015 at sites in Presque Isle and 

Alcona Counties, MI.

Weekly Mean of Target Passage Rates—At both 

sites, weekly means of nocturnal target passage 

rates were relatively high compared to diurnal 

target passage rates and both sites showed a 

generally increasing mean through mid-October. 

After mid-October, nocturnal migration rates 

declined. Weekly means of nocturnal TPR were 

consistently higher than weekly means of diurnal 

TPR (Figures 15). As the recorded migration 

season began, there was less difference between 

the nocturnal and diurnal target passage rates 

(Figures 15 and 16), but the difference at the end of 

the recorded migration season was still substantial. 

Trends in both nocturnal and diurnal TPRs 

(7-day moving means) were similar at both sites 

(Figure 17).

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. Altitude profiles for dawn and night 

differed between our two locations, with density 

at low elevation being greater at our Presque Isle 

County site (Figures 18 and 19). Hourly altitude 

profiles at night revealed considerable variation in 

use of altitude bands (Figures 20 and 21); however, 

over the course of the season, the 100—150 m 

altitude band was observed to be the most densely 

used at both sites (Figure 22), with a total of 4.60 

targets per 1,000,000 m3

 per night-hour and 3.45 

targets per 1,000,000 m3 per night-hour, at Presque 

Isle County and Alcona County, respectively. The 

maximum density of targets was below 150 m during 

79.7% and 65.1% of the nights at the Presque Isle 

County and Alcona County, respectively (Figure 

23). A similar pattern, although with more variation, 

occurred if the hours from 20:00—04:00, with the 

maximum density of targets occurring at less than 

150 m during 51.1% and 49.6% of these night hours 

at the Presque Isle County and Alcona County, 

respectively (Figure 24).

At both sites, targets were observed within the 

entire range of altitude bands sampled. Mean 

altitude of nocturnal targets was 528 m ± 435 m 

SD and 681 m ± 502 m SD above ground level at 

our Presque Isle County and Alcona County sites, 

respectively. Median altitude at night was 377 m and 

533 m above ground level at the Presque Isle County 

and Alcona County sites, respectively. Median 

altitude was greatest during the night and dawn 

biological time periods. While many radar reports 

include estimates of mean and median altitude of 

targets, we found that these estimates were poor 

indicators of maximum density (Table 5) due to the 

difference in volume of sampled air space at various 

altitude bands.

Mean altitude per hour during the season showed 

a similar pattern at the two locations (Figure 25). 

Mean altitude increased following dusk, tapered 

around the 20:00 and 22:00 hours, and decreased 

following midnight. A spike in mean altitude 

occurred during the 06:00 hour, which corresponds 

to the dawn or near dawn during at least a portion 

of the survey period. Density of targets was 

highest during the nighttime hours. However, the 

highest density of targets was below 500 m for the 

Presque Isle County site (Figure 26), and below 

800 m for the Alcona County site (Figure 27). These 

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density findings show the distribution of migrants 

is most dense at lower altitudes. Importantly, 

density distributions are skewed and mean altitude 

measures do not accurately reflect the underlying 

distribution of migrants at these sites.

Figure 15. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in Presque Isle 

County (top row) and Alcona County (bottom row) from August 7-October 23, 2015. Error bars represent 

one standard deviation. Note different scales on nocturnal and diurnal plots.

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Figure 16. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during fall 2015 in Presque Isle County (top row) and Alcona County (bottom row).

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Figure 17. Comparison of nocturnal (top row) and diurnal (bottom row) target passage trends (based on a 

moving 7-day mean) during fall 2015 in Presque Isle County and Alcona County, MI.

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 Presque Isle 

County and Alcona County during fall, 2015. Max band densities represent the top of the altitude band.

Presque Isle Alcona 

Biological Mean Median Max Band Mean Median Max Band

Period Density Density

Dawn 594 ± 491 401.27 250 680 ± 544 486.92 350

Day 392 ± 340 292.61 300 475 ± 445 344.12 350

Dusk 314 ± 331 237.44 150 365 ± 364 269.90 250

Night 528 ± 435 377.34 150 681 ± 502 533.40 150

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Figure 18. Altitude profile of targets at our site in Presque Isle County, MI. 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). Tan band represents the rotor swept zone (RSZ) between 30—200 m. Y-axis labels represent the top 

of the altitude band.

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26 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 19. Altitude profile of targets at our site in Alcona County, MI. 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). 

Tan band represents the rotor swept zone (RSZ) between 30—200 m. Y-axis labels represent the top of the 

altitude band.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 27

Figure 20. A sample of hourly altitude profiles corrected for the shape of the sample volume at our 

site in Presque Isle County, during fall 2015. 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 200 m. Y-axis labels represent the top of the altitude 

band.

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28 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 21. A sample of hourly altitude profiles corrected for the shape of the sample volume at our 

site in Alcona County during fall, 2015. Hours were selected to portray the variability in density per 

altitude band of passing targets. The x-axis represents target density. Y-axis labels represent the top 

of the altitude band.

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Figure 22. Altitude profile of corrected target density below 400 meters in Presque Isle County and Alcona 

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

labels represent the top of the altitude band.

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30 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 24. 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 Presque Isle County and Alcona County, during fall 2015. X-axis labels 

represent the top of the altitude band.

Figure 23. 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 Presque Isle 

County and Alcona County, during fall 2015. X-axis labels represent the top of the altitude 

band.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 31

Figure 25. Mean hourly target heights (m) in fall 2015 in Presque Isle and Alcona Counties, Michigan. 

Orange and blue markers indicate the hours in which sunrise and sunset occurred during the season, 

respectively. Error bars represent one standard deviation.

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32 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 26. Variation in flight Altitudes based on target density (targets per million cubic m) at our site in 

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

represent the max value of each altitude band. Density of targets is in targets per million cubic meters. 

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 dotted line at 200 m represents maximum height of a turbine with a rotorswept zone of 30-200 m. Note difference in density scale used in Figure 27.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 33

Figure 27. Variation in flight Altitudes based on target density (targets per million cubic m) at our site 

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

represent the max value of each altitude band. Density of targets is in targets per million cubic meters. 

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 dotted line at 200 m represents maximum height of a turbine with a rotorswept zone of 30-200 m. Note difference in density scale used in Figure 26.

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34 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 28. Movement direction of targets for each night over the spring 2015 migration season for Presque 

Isle site. Each line represents the average origin direction of targets during one night. These directions are 

averaged across the night, and while orientation changes throughout the night, provide a general direction 

of flight. Line length is proportional to number of targets moving through the area. Line color denotes the 

time within the season, with cooler colors denoting later dates in the season. Note the variety of origin 

directions, and the relatively common movements from the east across open waters of Lake Huron.

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Results-Spring 2016

During the spring 2016 season we began data 

collection March 29 at both sites. Data collection 

ended on June 13, and June 14 at Presque Isle 

County and Alcona County, respectively, resulting 

in a survey period of 1870 hours at the Presque Isle 

County site and 1847 hours at the Alcona County 

site (Table 2). Data were recorded continuously 

while the radar units were operational. Gaps in 

analyzed data occurred during rain events and 

when the radar units were not operational due to 

maintenance or malfunction (radar downtime). 

Horizontal radar at Alcona County site was lost due 

to motor and gear damage from March 29-April 22. 

When correcting for radar downtime and removal of 

periods with rain, the radars collected useable data 

77% and 95% of the season in Presque Isle County 

and 84% and 65% in Alcona County with the vertical 

and horizontal radars, respectively.

Qualitative Assessments

Plots of tracked targets showed images of nocturnal 

migration events at both locations (Figure 29-30). 

For example, on May 9 at the Presque Isle County 

site (Figure 29), the horizontal radar recorded 

scattered activity, and low activity was present 

on the vertical radar between 12:00 and 18:00. 

During 20:00-21:00, the horizontal radar recorded 

a direction shift to north and northeast, and the 

vertical radar recorded many more targets in the 

air, especially at and below 1250 m. The direction 

stayed consistently northward through 01:00 

on May 10th, while the vertical radar recorded a 

second dense band of migrants from 1750-2250 

m beginning at 23:00 on May 9th. The number of 

migrants recorded on the vertical radar began to 

decline after this point, continuing through 04:00. 

Table 6. Survey effort (hours) by vertical and horizontal scanning radars during spring 2016 at our radar 

sites in Presque Isle County and Alcona County.

Site Radar Survey Radar Time Radar Radar Data Usable % Usable

 Period Downtime1 Collected Data w/Rain Radar Data Data

Presque Isle VSR 1870 255 1615 186 1429 76%

Presque Isle HSR 1777 0 1777 22 1755 99%

Alcona VSR 1847 45 1801 254 1548 84%

Alcona HSR 1847 607 1240 47 1193 65%

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

The horizontal radar recorded a shift in direction at 

04:00 towards the west, chiefly among migrants over 

water, indicating a dawn return towards shore. This 

pattern continued and strengthened through 05:00. 

The number of targets recorded by vertical radar 

continued to decline over this time. By 12:00 on May 

10th, the pattern had returned to a similar pattern as 

the previous day, with few targets moving in no clear 

direction. The pattern from May 9-10 is consistent 

with previously observed nocturnal migratory 

activity in the spring.

Migratory activity in Alcona County on the night 

of 29 April-30 April (Figure 30) are broadly 

similar to those at Presque Isle County, including 

low number of migrants with little directionality 

recorded at 12:00, and increase in number of targets 

and directionality starting at 20:00 and peaking at 

01:00 on April 30, then declining during the rest 

of the night and returning to low numbers and no 

directionality by 12:00. During 05:00 of April 30th, we 

recorded a very clear dawn turn towards shore, with 

all individuals over water turning west, while targets 

at the shore demonstrated a strong north-south 

pattern, indicative of targets following the shoreline, 

presumably searching for suitable stopover habitat.

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 4b) resulting in 

reduced detection in the air space that was within 

the range of data collection (e.g., southwest of the 

radar unit at the Presque Isle County site and in the 

areas in the northwest areas of the Alcona County 

radar site as seen in the horizontal Trackplots; 

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36 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Trackplots (seen at a range of about 1,400—2,000 m). 

Additionally, there was low-elevation clutter on one 

side of the Alcona County’s VSR, reducing detection 

on lakeward side of the radar.

Figures 29 and 30). 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 (e.g., April 29-30, 20:00-05:00. Figure 

29) and vertical (e.g., May 9th, 23:00. Figure 28) 

Figure 29. Images of tracks during 1-hour increments recorded by horizontal and vertical scanning radars 

during a migration event at our radar site in Presque Isle County. Horizontal radar images (columns 1 

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

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

May 9, 12:00

May 9, 20:00

May 10, 01:00

May 10, 05:00

May 9, 18:00

May 9, 23:00

May 10, 04:00

May 10, 12:00

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Figure 30. Images of tracks during 1-hour increments recorded by horizontal and vertical scanning radars 

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

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

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

April 29, 12:00

April 29, 20:00

April 30, 01:00

April 30, 05:00

April 29, 18:00

April 29, 23:00

April 30, 04:00

April 30, 12:00

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directionality at night was slightly stronger at our 

Presque Isle site than in our Alcona site (Table 7). 

Directional trends also refl ect movement towards 

shore at dawn. The Presque Isle site is located on 

a northwest to southeast oriented shoreline, while 

Alcona is located on a north-south oriented shoreline 

(Figure 1). During the dawn time period, Presque 

Isle shows a substantial movement to the south and 

southwest, refl ecting the movements of migrants 

from open water to the north or the site to shore, 

whereas the Alcona site shows migrants oriented to 

the north and northwest, consistent with migrants’ 

movement into shore from the open waters to the 

east. Migrants appear to be moving from the south 

directly across the lake at the Presque Isle site 

(Figure 49), while they tend to follow the western 

shore of Lake Huron at our Alcona site (Figure 50).

Directional Trends

During the spring 2016 season, nocturnal target 

movement direction was generally north/northeast 

at both sampled locations (Figure 31). At the 

Presque Isle County site, mean nocturnal direction 

was 18° with an angular concentration (r) of 0.47 

(n = 2,265,807 targets) and during 59.3% of nights 

mean target direction was between northwest and 

northeast (292.5°—67.5°). Direction at the Alcona 

County site had a mean nocturnal direction of 

9° (r = 0.39, n = 2,324,169) with 67% of nights 

having a mean direction between northwest and 

northeast. Onshore movement to the west and 

south at dawn was visible at Presque Isle County, 

while onshore movement to the west was visible 

at dawn at Alcona County (Figure 30). Uniform 

Target Direction per Hour During Four Biological Time Periods

Figure 31. Target direction per hour during four biological periods during spring 2016 at our sites in 

Presque Isle (left) and Alcona Counties (right). Note the different scales on each of the graphs.

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

directionality (r ≥ 0.5) of targets during biological time periods at our sites in Presque Isle and Alcona 

counties.

Presque Isle Alcona

Biological Mean % time Mean % time

Period Direction r r ≥ 0.5 n Direction r r ≥ 0.5 n 

 (degrees) (degrees) 

Dawn 243 0.20 32.9% 146,863 318 0.44 61.3% 165,023

Day 311 0.27 17.3% 1,090,186 357 0.21 18.8% 1,116,667

Dusk 1 0.55 54.1% 95,352 35 0.49 46.9% 37,494

Night 9 0.39 27.8% 2,324,169 18 0.47 59.3% 2,265,807

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Different patterns of activity are apparent as the 

season progresses at our study sites. For example, 

beginning in mid-April activity patterns become 

dominated by nocturnal pulses that are seen on 

both horizontal and vertical radars in Presque 

Isle County, and in Alcona County to a lesser 

extent. This pattern continues until late May when 

activity patterns begin to shift with activity levels 

decreasing overall.

Temporal Trends

Time Series Plots—Hourly target counts provided 

by horizontal and vertical radars showed pulses of 

elevated nocturnal activity with peaks occurring 

around midnight at our study sites. Across our 

sampling period these events were often clustered 

into groups of several nights and were first observed 

on April 14 and April 16 at the Presque Isle and 

Alcona counties, respectively (Figures 32 and 33). 

At both sites, the occurrence and magnitude of 

nocturnal pulses decreased substantially after 

May 30, 2016.

Figure 32. Hourly counts by horizontal and vertical radars from March 29-June 3, 2016 

Presque Isle County, MI. Light gray vertical lines represent midnight. figure 32 title: 

Hourly Counts by Horizontal and Vertical Radars: Presque Isle County, MI

Hourly Counts by Horizontal and Vertical Radars: Presque Isle County, MI

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40 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Hourly Counts by Horizontal and Vertical Radars: Alcona County, MI

Figure 33. Hourly counts by horizontal and vertical radars from March 29-June 

13, 2016 in Alcona County, MI. Light gray vertical lines represent midnight.

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nights) at the Presque Isle and Alcona counties, 

respectively. Mean TPR varied by hour with peak 

numbers reached during the 21:00 and 00:00 hours 

(approximately dusk through three hours after 

sunset) at both sites. At both locations, mean TPR 

gradually decreased as the night progressed, with 

the most drastic decline occurring around 04:00 and 

05:00, which corresponds with dawn (Figure 35).

insert figure 34 (2 pieces)

Target Passage Rate—The pattern of mean TPR 

among the four biological time periods was similar 

between the two study sites (Figure 33), with mean 

TPR at night being greater than the combined 

means of the other three biological time periods 

(Table 8). Mean nocturnal TPR was 583.6 ± 737.5 

SD (n = 58 nights) and 461.7 ± 488.0 SD (n = 74 

Figure 34. Box plots showing variability in target passage rate (targets/km/hr) during four biological 

periods for spring 2016 in Presque Isle and Alcona counties, Michigan. Whiskers represent the 1st and 

4th quartiles, boxes represent the 2nd and 3rd quartiles (with the line between indicating the median), 

and blue diamonds represent seasonal mean for the time.

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

Presque Isle and Alcona Counties during spring 2016.

Biological Period Presque Isle Mean TPR Alcona Mean TPR

Dawn 43 ± 71 160 ± 222

Day 155 ± 212 30 ± 29

Dusk 38 ± 75 15 ± 14

Night 404 ± 736 462 ± 488

Figure 35. Mean hurly target passage rate (targets/km/hr) during spring 2016 at sites in Presque Isle and 

Alcona counties, MI.

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between the nocturnal and diurnal target passage 

rates (Figures 36 and 37). Trends in both nocturnal 

and diurnal TPRs (7 day moving means) were 

similar in pattern, but not magnitude at both sites 

(Figure 37). Presque Isle County had a slightly 

higher target passage rate during migration peaks, 

especially night migration peaks than Alcona County 

(Figures 34, 38).

Weekly Mean of Target Passage Rates—At both 

sites weekly means of nocturnal target passage 

rates were relatively high compared to diurnal 

target passage rates and both sites showed a 

generally increasing mean throughout the season. 

In mid-to-late May nocturnal mean TPRs began to 

decrease (Figure 36). Weekly means of nocturnal 

TPR were consistently higher than weekly means 

of diurnal TPR (Figures 36). As the recorded 

migration season subsided there was less difference 

Figure 36. Weekly mean of nocturnal and diurnal target passage rates (targets/km/hr) in Presque Isle (top 

row) and Alcona (bottom row) counties from April 1-June 10, 2016. Error bars represent one standard 

deviation. Error on 9-June for Alcona’s nocturnal passage rate is too small to be graphed with the other 

weeks. Note different scales on nocturnal and diurnal plots.

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Figure 37. Comparison of nocturnal and diurnal target passage trends (based on a moving 7-day mean) 

during spring 2016 in Presque Isle (top row) and Alcona (bottom row) counties.

A similar pattern, although with more variation, 

occurred if the hours from 20:00—04:00 were 

considered individually, with the maximum density 

of targets occurring at less than 200 m during 56.3% 

and 43.2% of these night hours at the Presque Isle 

and Alcona site, respectively (Figure 45).

At both sites, targets were observed within the 

entire range of altitude bands sampled. Mean 

altitude of nocturnal targets was 790 m ± 401 m 

SD and 731 m ± 533 m SD above ground level at 

our Presque Isle and Alcona sites, respectively. 

Median altitude at night was 618m and 577 m above 

ground level at the Presque Isle and Alcona sites, 

respectively. Median altitude was greatest during 

the night and dawn biological time periods. While 

many radar reports include estimates of mean and 

median altitude of targets, we found that these 

estimates were poor indicators of maximum density 

(Table 9) due to the difference in volume of sampled 

air space at various altitude bands.

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, as is the case with reporting 

uncorrected counts. Altitude profiles for dawn 

and night differed between our two locations with 

density at low elevation being greater at our Alcona 

site (Figures 39 and 40). Hourly altitude profiles 

at night revealed considerable variation in use of 

altitude bands (Figures 41 and 42); however, over 

the course of the season the 150 m altitude band was 

observed to be the most densely used at the Presque 

Isle and Alcona counties (Figure 43) with a total of 

2.15 targets per 1,000,000 m3

 per night-hour and 3.56 

targets per 1,000,000 m3 per night-hour, respectively. 

The maximum density of targets was below 150 m 

during 85.3% and 71.6% of the nights at the Presque 

Isle and Alcona sites, respectively (Figure 44). 

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44 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 38. Comparison of nocturnal (top row) and diurnal (bottom row) target passage trends (based on a 

moving 7-day mean) during spring 2016 in Presque Isle and Alcona counties, Michigan.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 45

Mean altitude per hour during the season showed 

a similar pattern at the two locations (Figure 46). 

Mean altitude increased following dusk, tapered 

around the 21:00 and 22:00 hours, and decreased 

following midnight. A spike in mean altitude 

occurred during the 05:00 and 06:00 hour in at 

both sites. These time periods occur during or 

near dawn during at least a portion of the survey 

period (Figure 46). Altitude also varied in density 

among time across the season. At the Presque Isle 

site (Figure 47), the greatest density of migrants 

occurred during the nocturnal hours, and migrants 

generally were most dense at less than 300 meters, 

suggesting heavy use of the lower airspace. High 

migrant density expanded to higher altitudes 

during dawn and dusk periods, suggesting that 

migrants may fly higher during these times to 

orient for nightly migration at dusk and towards 

safe habitat at dawn. Likewise, the Alcona site had 

the highest density of migrants during nocturnal 

hours and migrant density was highest below 350m 

(Figure 48). However, there is no expansion of high 

density at dawn and dusk at Alcona. One possible 

explanation for this difference is the presence of a 

water crossing north of the Presque Isle site that 

may require migrants to inspect and orient to the 

crossing, while they can follow the shoreline at the 

Alcona site.

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 Presque Isle and Alcona Counties during spring 2016. Max band densities represent the top of the 

altitude band.

Presque Isle, MI Alcona, MI 

Biological Mean Median Max Density Mean Median Max Density

Period Band Band 

Dawn 763 ± 551 595 150 737 ± 501 610 150

Day 437 ± 398 316 150 527 ± 478 376 100

Dusk 395 ± 401 244 200 731 ± 466 177 150

Night 790 ± 574 618 150 731 ± 533 577 200

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Figure 39. Spring altitude profile of targets at our site in Presque Isle 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 Tan band represents the rotor swept zone (RSZ) between 30—200 m. Y-axis 

labels represent the top of the altitude band.

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Figure 40. Spring altitude profile of targets at our site in Alcona County. 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). Tan band represents the rotor swept zone (RSZ) between 30—200 m. Y-axis labels represent the top 

of the altitude band.

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Figure 41. A sample of hourly profiles corrected for the shape of the sample volume at our site in Presque 

Isle Co. during spring 2016. 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 200 meters. The Y-axis represents the top altitude.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 49

Figure 42. A sample of hourly altitude profiles corrected for the shape of the sample volume at our site in 

Alcona counties during spring 2016. 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 200 m. Y-axis labels represent the top of the altitude band.

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Figure 43. Altitude profile of corrected target density below 400 meters in Presque Isle and Alcona counties. 

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

the top of the altitude band.

Figure 44. 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 Presque Isle and Alcona counties, during 

spring 2016. X-axis labels represent the top of the altitude band.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 51

Figure 45. 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 Presque Isle and Alcona 

Counties, during spring 2016. X-axis labels represent the top of the altitude band.

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Figure 46. Mean hourly target height (m) during spring 2016 in Presque Isle and Alcona Counties. Orange 

and blue markers indicate the hours in which sunrise and sunset occurred during the season, respectively. 

Error bars represent one standard deviation.

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Figure 47. Variation in flight altitudes based on target density (targets per million cubic m) at our site in 

Presque Isle throughout the spring study period. Altitude bands are in meters and labels represent the max 

value of each altitude band. Density of targets is in targets per million cubic meters. 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 dotted line at 200 m represents the maximum height of a turbine with a rotor-swept zone of 70-200 m. 

Note difference in density scale used in Figure 48.

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54 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Figure 48. Variation in flight altitudes based on target density (targets per million cubic m) at our site in 

Alcona County throughout the spring study period. Altitude bands are in meters and labels represent the 

max value of each altitude band. Density of targets is in targets per million cubic meters. 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 dotted line at 200 m represents the maximum height of a turbine with a rotor-swept zone of 

70-200 m. Note difference in density scale used in Figure 47.

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Figure 49. Movement direction of targets for each night over the spring 2015 migration season for Presque 

Isle site. Each line represents the average origin direction of targets during one night. These directions are 

averaged across the night, and while orientation changes throughout the night, provide a general direction 

of flight. Line length is proportional to number of targets moving through the area. Line color denotes 

the time within the season, with cooler colors denoting later dates in the season. Note the more consistent 

direction of travel during the spring season compared to the fall (Figure 28).

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Figure 50. Movement direction of targets for each night over the spring 2015 migration season for Alcona 

County. Each line represents the average origin direction of targets during one night. These directions are 

averaged across the night, and while orientation changes throughout the night, provide a general direction 

of flight. Line length is proportional to number of targets moving through the area. Line color denotes the 

time within the season, with cooler colors denoting later dates in the season. Note the majority of migrants 

are following the western shoreline of Lake Huron north.

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Discussion

documents various aspects of migration and 

identifies Great Lake shorelines as important areas 

for the 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.

Loss of the horizontal radar at our Alcona County 

site limited observations to only the vertical radar 

for the duration of the fall 2015 season and the 

first 3.5 weeks of the spring 2016 season. However, 

vertical radar still provided substantial information 

on migration onset and conclusion, accurate counts 

of the number of targets observed, and altitudinal 

distribution of targets at the Alcona County site.

We undertook this study to document migration 

along the shorelines of the Great Lakes. The fall 

2015/spring 2016 seasons were the first time we 

stationed the radar units at the same sites for two 

consecutive migration seasons. By placing radars 

at the same sites for two consecutive seasons, we 

can more closely compare the similarities and 

differences between spring and fall migration. 

Overall, what we found indicates migration 

movements were common along the northwestern 

shorelines of Lake Huron, where we established 

our study sites. In addition, we believe that data 

collected at these two sites are representative 

of migration along the rest of the Lake Huron 

shorelines in the United States. Our research 

contributes to a growing body of literature that 

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 August 3-October 27, 2015 in Presque Isle, 

Michigan.

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Migration Patterns

Patterns of movement we recorded were consistent 

with other observations of migration (Newton 2008) 

and indicated that nocturnal migratory flights 

occurred regularly during both fall 2015 and spring 

2016 at both of our surveyed locations. During the 

fall season, the nocturnal activity we observed was 

typically oriented in a north/northeast direction 

(Figures 10 and 31) and occurred in pulses across 

the season that were captured by horizontal and 

vertical radars (Figures 11, 12, 32, 33).

We also observed targets returning to shore 

from open water at dawn (Figure 8, 29, 30). This 

movement to shore may be due to migrants drifting 

with the wind as they migrate and adjusting their 

position at dawn to locate suitable stopover habitat 

to rest a refuel (A. Peterson, pers. communication, 

Horton et al. 2016). Target passage rate (mean 

for the season) was greatest during the nocturnal 

biological time period at both locations (Tables 4, 8; 

Figures 13, 34). At each of our sites, mean hourly 

heights showed a pattern consistent with migration 

(Harmata et al. 2000, Mabee and Cooper 2004), 

with heights that increased near dusk, peaked a 

few hours before midnight, and began to decrease 

prior to dawn. Presque Isle County’s mean hourly 

height pattern was similar to other locations we 

have investigated; however, the highest mean 

altitudes were recorded during dawn and not 

midnight (Figure 25). This could be driven by the 

location of the coastline at the site, which may act as 

a refuge point both for migrants moving south from 

the open water to the north, as well as individuals 

turning west towards shore from open water to the 

east. Targets at the Alcona County site in the fall 

and both Alcona County and Presque Isle County 

sites during the spring increased in mean height 

near dawn (Figures 25 and 26), 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. However, 

this may also be an artifact of averaging the dawn 

hours across the season. We are undertaking further 

studies to tease this apart. Taken together, we 

attribute these nocturnal observations to migrants 

and suggest that the shorelines we studied are 

important for their conservation.

During the fall season, nocturnal migrants moved 

across the landscape in several major waves. For 

Presque Isle County, three major waves moved 

through, centered on the dates of September 24, 

September 30, October 8, and October 10. The 

Alcona County showed slightly different timing 

of waves at September 20, September 30, October 

8 and October 16. In all cases, the Presque Isle 

County events tended to occur on a single night 

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, 

McGuire et al, 2012b). Our continuous sampling 

scheme captured the timing of migration events and 

provided a more complete picture of the migratory 

season than a systematic (e.g., once per week) or 

random sampling scheme, which may have missed 

pulses of activity, even at relatively high resolution 

(e.g., sampling once every four days, Figure 48). 

We used diurnal radar observations to provide 

a baseline for comparing nocturnal activity, and 

including this time period in the sampling scheme 

helped to distinguish the magnitude of migration 

events (Figures 11-12; 31-32). Our sampling regime 

in fall 2015 indicated that migration season began 

in late August, peaked in mid to late-September 

and declined by mid-October, although migration 

continued to occur sporadically through the end of 

sampling. In spring 2016, the migration occurred 

mainly during the month of May, although sporadic 

migration events also occurred during April and 

June as well. This information will help to tailor 

conservation efforts to appropriate time frames 

for migratory birds and bats.

Target Counts

Target counts provided by radar are influenced 

by radar type and calibration, filtering of nonintended targets, tracking 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 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 nocturnal passage rates 

showing peaks much larger than the nocturnal 

lulls for most of the sampling period may be 

considered to have stronger migration than sites 

with less discrepancy between the peaks and lulls. 

A site where there were only occasional spikes of 

activity rather than more common spikes may be 

indicative of an area with lower migration, although 

this method may not be appropriate for all sites. 

The presence of behavioral indicators of obstacles, 

including movement to or along shore during dawn, 

and changes in direction of movement during the 

night suggest that these shorelines may indicate a 

risk to migrants in the area, along with more specific 

measures such as density of targets in the rotorswept zone.

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lower altitudes where wind speeds were reduced 

(Gauthreaux 1991). As well, 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 or descending to stopover 

sites. Depending on location, these altitude changes 

may place migrants at risk of collision with wind 

turbines and other tall human-made structures.

Comparison of Spring and Fall Migratory Seasons

Migration rates were different in the spring and 

fall at these sites. While fall migration appeared 

to occur in more episodic fashion, spring migration 

was continuous and stable. There are a number 

of potential reasons for these differences. First, 

fall migration strategies could reap benefits by 

waiting for more favorable weather. Second, this 

strategy could be increased by an overall higher 

body condition from ample food resources on the 

breeding grounds. In contrast, this episodic nature 

could be due to more difficult crossings of ecological 

obstacles in the fall, necessitating more favorable 

weather conditions for crossing, or due to other 

behavioral factors (e.g., fall mating seasons in the 

case of migratory bats; Cryan and Brown 2007). 

Naïve migrants (e.g., young of the year) may also 

use different strategies than experienced migrants, 

causing larger pulses. Spring migrants, especially 

male birds, are often attempting to reach breeding 

ground early in order to attempt to acquire the best 

possible territory for the breeding season, which 

may motivate migrants to cross ecological obstacles 

during less than optimal conditions (Francis and 

Cooke 1986, Dierschke et al. 2005). Combined with 

females following the males during warmer periods, 

this could produce the more consistent migration 

pattern we observe in the spring. What drives 

differences in migration tempo between spring and 

fall migration season merits further attention.

For horizontal radar directionality, we can only 

compare the Presque Isle County site between 

the seasons. We found that direction was oriented 

broadly south in the fall and north in the spring 

(Figures 8-10; 29-31). However, the mean circular 

concentration, r, providing a measure of uniformity 

of movement showed that during day and dusk, 

the r of movement directions was much higher 

in spring than in fall (Tables 3, 7). While the 

reasons for the stronger daytime concentration 

are unclear, the dusk concentration may indicate 

faster navigational orientation. Studies of migrants 

and homing birds found that juvenile birds tend 

to orient less accurately than adults, which could 

reduce concentration (Moore 1984). Thus, the spring 

increase in mean angular concentration could be due 

to the lack of naive birds in the population in spring 

compared to the fall.

or very few nights with little or no buildup, while the 

Alcona County site showed more gradual buildups 

to the peak dates. The differences between these 

sites may be due to optimal conditions in crossing 

the water barriers to the north of the Presque 

Isle County, which would suggest that migrants 

concentrate along the north edge of Lake Huron 

before moving across en masse during only the 

most favorable conditions, while migrants may 

continue to move south along the shore during times 

when weather conditions are still favorable, but not 

necessarily optimal.

During the spring season, fluxes of night migrants 

moved more consistently than the fall, with fewer 

pulses. At our Presque Isle County site, there was 

a large spike of migrants May 10–12, followed by a 

lower, but consistent set of peaks from May 16–29. 

Our Alcona County site did not demonstrate a spike 

of migration, and instead had consistent nightly 

migration from May 10 to June 4. We speculate 

the spike in migration at the Presque Isle County 

site may be due to migrants waiting for favorable 

conditions early in the season, but this explanation 

does not account for the consistent pattern of 

migration afterward.

Flight Altitude

Altitude profiles indicated that most nocturnal 

targets passed below 800 m with peak density in the 

150-250 m altitude bands (Figures 18, 19, 21, 39, 40, 

and 43). We corrected for the approximate shape 

of the survey volume and included this correction 

in our density estimates. This correction is based 

on the manufacturer’s estimate of beam geometry, 

which may not be precise, and beam propagation 

is not consistent over time. Beam propagation is 

affected by side lobes, target size and distance, and 

atmospheric conditions. Nonetheless, we think the 

correction was an improvement over altitude profiles 

that ignore beam geometry and sampling effort. 

We were not able to correct for the loss of detection 

with distance from the radar (Schmaljohan et al. 

2008); in addition, our vertical scanning radars had 

reduced detection at a range of about 1,400–2,000 

m where the radar transitioned from the short to 

medium pulse. For these reasons, our estimates 

likely under-represent density as altitude increases. 

There is a minor increase around 1,400 m that 

might be undercounted during night migrations 

(e.g. Figure 18), but is unlikely to change the 

overall picture.

Altitude profiles that we report varied considerably 

among nocturnal hours at our sites in Alcona and 

Presque Isle Counties (Figures 19, 20, 41, 42). 

Migrants adjust flight altitude with wind direction, 

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 

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60 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

that are derived from these data. This presents 

a challenge that is not easily solved. Yet, without 

standards, comparisons among studies may be more 

reflective of differences in equipment, methodology, 

and site conditions rather than differences in 

migration activity.

An example of a potentially misleading metric, mean 

altitude of target passage, is often reported to be 

above the rotor-swept zone and has been interpreted 

as an indication of low risk. However, the mean 

altitude can be well above the rotor-swept zone even 

when there is a high rate of targets passing within it. 

This is due to the long range at which radars collect 

altitude data, up to 3 km above ground level in our 

study, where high-flying targets inflate the mean 

altitude. This bias is apparent in our data and can be 

seen by comparing the mean altitude of nocturnal 

targets to the most densely populated altitude band 

(Tables 5 and 9; also see Figures 26–27 and 47-48). 

We do not recommend using mean and median 

altitudes as indicators of risk to migrants.

It is also misleading to compare the percent of 

targets below, within, and above the height of the 

rotor-swept zone without addressing the difference 

in sampling effort between these categories. 

Within our sampling framework, there are four 

50-m altitude bands below 200 m (an estimate 

for the height of the rotor-swept zone) and 52 

altitude bands above 200 m. Based on our model, 

we estimated that approximately 2 percent of the 

potential survey volume is below 200 m. Given that 

information, we would expect a small percentage of 

targets to be recorded at or below the rotor-swept 

zone, but this does not necessarily indicate low risk. 

If targets were spread evenly throughout the survey 

volume, we would expect to have a tiny percentage 

of targets within the rotor-swept zone. Uncorrected 

numbers such as 5–10% of targets in the rotor-swept 

zone are often reported and classified as “low risk” 

due to the low percentage of targets in the rotorswept zone, even though this means that this area 

is many times more concentrated with targets than 

we would expect from a random distribution of 

targets throughout the survey volume. When using 

estimates of target counts that are corrected for 

volume, we often see a much higher concentration 

in the rotor-swept zone than if the numbers do not 

take sampling volume into account (Figures 23-27; 

Figures 44-48). For these reasons, we also do not 

recommend using percentages of targets below, 

within, or above the rotor-swept zone as indicators 

of risk to migrants.

In this report, we provide examples of methodology 

and analyses that we find helpful in interpreting 

radar data and which we have used in other seasons. 

We suggest that the patterns of activity and the 

relative change in counts at a site indicate the 

level of migration activity and that this is a better 

We found that altitudes at both sites were on 

average similar in densities among altitude bands 

at both sites for most of the night (Presque Isle: 

Figures 26 and 47; Alcona: Figures 27 and 48) 

among seasons. However, during the spring 

season at Presque Isle we found a strong increase 

in density across altitude bands at dusk hours. 

Additionally, during the fall season we observed 

a more modest increase in density across altitude 

bands at the Alcona site. We speculate that for both 

sites, this phenomenon may be due to migrants 

increasing flight altitudes in order to orient and 

determine crossing lengths across open water. At 

Presque Isle, for instance, there is a high density of 

migrants at dusk to ~400-m altitude, with density 

gradually reducing above this altitude. At 400 m, 

the horizon is calculated to be at 71 km (assuming 

no diffraction), well past the 60 or so km to the 

northern coastline of Lake Huron. Likewise, the 

Alcona site data shows a similar increase in the fall, 

which could be due to migrants orienting to cross 

either Lake Huron (133 km across) or Saginaw Bay 

(76 km across). Future work comparing spring and 

fall density spikes at other crossings could help 

establish if this is a widespread pattern.

We emphasize that these findings are from only two 

sites for two seasons, and should not be generalized 

without caution. Site-specific attributes (e.g., 

Presque Isle County’s two large water crossings), 

anomalous weather in one or both seasons, and 

interannual variation in migration patterns, singly 

or together could be driving a large amount of 

what we perceive as the interseasonal patterns. 

In addition, differences in migratory behavior 

among species and taxa (e.g., birds vs. bats) cannot 

be disentangled solely with radar data. Finally, 

differences in detectability among sites make it 

difficult to directly compare sites in a quantitative 

manner. Additional work needs to be done to 

quantify and correct detectability differences so 

further comparisons with a larger sample of data 

across multiple sites and years in can be undertaken 

to tease apart the differences between spring and 

fall migrations.

Radar Study Considerations

While radar may be the best tool available for 

gathering large amounts of data on nocturnal 

migration, the interpretation of radar data can be 

challenging. The metrics reported in these types of 

surveys can be misleading to someone unfamiliar 

with avian radar. Marine radar is the most common 

type used to track bird and bat movements (Larkin 

2005), and its use to assess risk will likely increase 

with the increase in wind energy development. 

Despite this growing trend, standard methodologies 

for establishing radar settings, ground truthing 

biological targets, and processing data have not been 

adopted. These considerations can substantially 

affect the quality of data and the interpretations 

Avian Report.indd 70 7/24/18 6:2
Great Lakes Avian Radar Technical Report Lake Huron Shoreline 61

guilds, may be heading to different wintering areas, 

may be arriving from different breeding grounds, 

may have different physical conditions, or may 

represent different sex or age groups than those 

that previously migrated through the same area. 

Consequently, impacts to the shoreline area from 

development, habitat loss, or other factors may have 

impacts on all parts of the population for a wide 

variety of bird and bat species.

At the survey locations this season, our risk analysis 

revealed that during a large proportion of nocturnal 

hours or nights overall, the numbers and densities 

of birds and bats flying in or near the rotor-swept 

zone were high (Figures 22-24; 26-27;44, 45, 47, 48). 

Nocturnal and diurnal migrants change altitudes 

depending on environmental conditions, and thus, 

migrants in altitude bands that are near the rotorswept zone may also be at risk. In addition, our 

analysis only shows a typical rotor-swept zone for 

turbines constructed at the time of this study. Wind 

turbines are already being constructed to higher 

altitudes (Eller 2015), with larger rotor-swept zones 

extending into the altitude bands above where 

turbine blades currently reach, which will likely 

impact more migrants (Figures 26, 27, 47, 48).

Our data demonstrate that the shoreline areas of 

Lake Huron are important for migrating birds and 

bats. We have identified behaviors that concentrate 

migrants along the shoreline, demonstrated that 

these behaviors occur regularly throughout the 

season, and established that migrants are flying at 

altitudes that place them at risk of collision with 

current or future wind energy development in the 

area. The importance of shoreline areas highlights 

the need to avoid development in these migration 

corridors as recommended in the USFWS wind 

energy guidelines (USFWS 2012).

The results of our research highlight the potential 

role of radar in implementing recommendations 

from the USFWS wind energy guidelines (USFWS 

2012) to identify areas where impacts to wildlife 

would be minimized. We documented clear examples 

of migrant activity along studied shorelines on Lake 

Huron, and the density of targets at lower altitudes 

is a potential concern. The data we collected may 

be of interest to public and private entities that 

are involved with wind energy development and 

its potential placement in the Lake Huron area as 

well as the entire Great Lakes region. Coupling 

avian radar systems with other forms of research 

or using radar in conjunction with acoustic and 

ultrasonic monitors, as well as post construction 

fatality searches, may broaden the utility in making 

risk assessments and assessing wind energy 

developments.

indicator than comparing the magnitude of counts 

among studies. Careful attention should be given to 

how these indices fluctuate over fine temporal scales, 

such as hourly, as opposed to monthly or seasonal 

summaries. These fine-scale measures may show 

more times when risk to migrants could be high. The 

clutter maps we include provided information about 

our ability to detect targets at various altitudes, and 

it is important, particularly for risk assessment, 

that radar operators address their ability to detect 

targets at low altitude. We provide a concept for a 

method to account for the structure of the sample 

volume that, while not without limitations, provides 

a partial solution rather than ignoring the biases 

associated with sampling effort. Overall, we found 

that radar provides insight into nocturnal migration 

that would otherwise be unattainable, while 

continued development and careful interpretation 

will result in valuable contributions to the 

management and conservation of migrant birds 

and bats.

Management Considerations

These data provide a large picture of migration 

that we need to put in perspective. Our radars 

were located along the shoreline, which is the 

area where we can gain the best picture of many 

migrant behaviors. The general patterns along the 

shorelines of Lake Huron reveal that these areas 

are used heavily by nocturnal migrants during 

both spring and fall migration. This pattern of 

migration is evident from our sample Trackplots 

as well as the timelines from each of the sites. 

Beginning in late August, migration occurs on many 

if not most nights, and continued through the end 

of our observations in late October. We observed 

migrants coming over the open water to the shore 

in our Presque Isle County site, and following the 

shore south at both sites. spring migration season 

began in mid-April and continued until early June. 

We observed migrants following the shore of Lake 

Huron crossing the open water between Michigan’s 

lower and Upper Peninsula. They likely used the 

shoreline for navigation or were funneled through 

the area by geographical features. The movement 

of migrants along the shoreline implies that a wind 

energy facility or communication tower constructed 

in the shoreline area may be encountered by more 

than just migrants moving from the areas directly 

to the north or south.

A close look at the different biological time periods 

also reveals information about the importance of 

the shoreline area. The high levels of activity at 

both sites during dusk may represent birds and 

bats leaving their stopover habitat to continue with 

their migratory journey. High activity levels at dawn 

may be due to new migrants moving into land in 

the stopover habitat after moving into the area at 

night or coming in from flying over the water. These 

newly arriving birds and bats may be in different 

Avian Report.indd 71 7/24/18 6:2
62 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

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Appendices

Appendix 1: Fall 2015 and Spring 2016 Report Summary

Appendix 2: Percent Land Cover Associated with Study Sites and the 2006 National Land Cover

Database Classification

Appendix 3: Corrected Density per Hour by Biological Period

Appendix 4: Comparison of Static and Corrected Density Estimates

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Appendix 1

Fall 2015 and Spring 2016 Report Summary

■ Migration occurred on the western shoreline of Lake Huron during fall 2015 and spring 2016.

■ Migration was identified by uniformity of movement of direction (south in the fall, north in the spring) 

at night, high target passage rate, and typically a peaking of numbers near midnight

■ General patterns and timing of migration were similar between the sites sampled 

during the same period

■ Three main waves of nocturnal migration in the fall with highest concentrations near 

September 20, September 30, and October 8–16

■ Consistent nightly migration but no waves or pulses May 10–June 4, with a pulse at one site 

May 10–12

■ Date range of pulses that occurred during the fall migration season

■ Began on August 27 in Presque Isle County, MI and August 26 in Alcona County, MI

■ Ended on October 27 in Presque Isle County, MI and Alcona County, MI

■ Date range of migration that occurred during the spring migration season

■ Began on April 15 in Presque Isle County, MI and April 16 in Alcona County, MI

■ Ended on May 29 in Presque Isle County, MI and May 28 Alcona County, MI

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

■ Movement between southeast and west during the night at all locations

■ 65% of nights surveyed the mean direction of travel was between S and SW during fall at 

Presque Isle County, MI

■ 59% of nights surveyed the mean direction of travel was between NE and NW during spring at 

Presque Isle County, MI

■ 67% of nights surveyed the mean direction of travel was between NE and NW during spring at Alcona 

County, MI

■ Movement in towards and/or along the shore at dawn

■ Observed at both sites during both seasons

■ Highest target passage rate at night

■ Dawn ascent

■ Slight increase in height around dawn hours observed at all sites

■ Peak density of targets in volume corrected counts

■ Max density below 150 m during 79.7% of fall nights and 51.1% of fall night hours at Presque Isle 

County, MI

■ Max density below 150 m during 65.1% of fall nights and 49.6% of fall night hours at Alcona County, MI

■ Max density below 150 m during 85.3% of spring nights and 56.3% of spring night hours at Presque Isle 

County, MI

■ Max density below 150 m during 71.6% of spring nights and 43.2% of spring night hours at Alcona 

County, MI

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■ 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 band graphics 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

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Appendix 2

Percent Land Cover Associated with Study Sites and the 

2006 National Land Cover Database Classification

Classification Description

Water

Open Water — areas of open water, generally with 

less than 25% cover of vegetation or soil.

Perennial Ice/Snow — areas 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 singlefamily housing units.

Developed, Medium Intensity — areas with a mixture 

of constructed materials and vegetation. Impervious 

surfaces account for 50% to 79% of the total cover. 

These areas most commonly include single-family 

housing units.

Developed High Intensity — 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.

Percent landcover found within 3.7 km of radar locations at Presque Isle and Alcona County 

sites during fall 2015 and spring 2016 migration seasons

Percent Land Cover

National Landcover Class Presque Isle County % Alcona County %

Open Water 35% 34%

Developed, Open Space 3% 4%

Developed, Low Intensity 1% 3%

Developed, Medium Intensity 0% 1%

Developed, High Intensity 0% 0%

Barren Land 10% 2%

Deciduous Forest 10% 22%

Evergreen Forest 7% 10%

Mixed Forest 3% 4%

Shrub/Scrub 1% 1%

Herbaceuous 6% 3%

Hay/Pasture 0% 3%

Cultivated Crops 0% 1%

Woody Wetlands 19% 12%

Emergent Herbaceuous Wetlands 4% 0%

Classification Description for the 2006 National Land Cover Database (taken from http://www.mrlc.gov/nlcd06_leg.php; accessed 5/5/2014).

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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 grasslegume 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.

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Appendix 3

Corrected Density per Hour by Biological Period

Estimated density of targets by altitude band 

during spring biological time periods (dawn, 

day, dusk, night) in Presque Isle County, fall 2015 

(targets/1,000,000 m3

/time period).

Altitude

Band Dawn Day Dusk Night

50 0.0 0.0 0.0 0.0

100 0.3 0.2 0.3 1.6

150 0.6 0.2 0.8 4.6

200 0.7 0.3 0.7 4.5

250 0.9 0.3 0.6 4.2

300 0.9 0.3 0.6 3.9

350 0.5 0.2 0.3 2.7

400 0.4 0.1 0.2 2.2

450 0.3 0.1 0.1 1.7

500 0.2 0.1 0.1 1.3

550 0.2 0.1 0.0 1.1

600 0.2 0.0 0.0 0.9

650 0.1 0.0 0.0 0.7

700 0.1 0.0 0.0 0.6

750 0.1 0.0 0.0 0.5

800 0.1 0.0 0.0 0.4

850 0.1 0.0 0.0 0.3

900 0.1 0.0 0.0 0.3

950 0.0 0.0 0.0 0.2

1000 0.0 0.0 0.0 0.2

Estimated density of targets by altitude band during 

spring biological time periods (dawn, day, dusk, 

night) in Alcona County, fall 2015 (targets/1,000,000 

m3

/time period).

Altitude

Band Dawn Day Dusk Night

50 0.0 0.0 0.0 0.0

100 0.5 0.2 0.3 1.5

150 0.7 0.2 0.7 3.4

200 0.6 0.2 0.7 3.4

250 0.5 0.2 0.7 3.3

300 0.5 0.2 0.5 2.8

350 0.8 0.3 0.5 3.1

400 0.6 0.2 0.3 2.5

450 0.5 0.1 0.2 2.1

500 0.4 0.1 0.1 1.8

550 0.3 0.0 0.1 1.5

600 0.3 0.0 0.0 1.3

650 0.2 0.0 0.0 1.2

700 0.2 0.0 0.0 1.0

750 0.1 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 0.4

1000 0.1 0.0 0.0 0.4

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Estimated density of targets by altitude band 

during spring biological time periods (dawn, 

day, dusk, night) in Presque Isle County, 

Spring 2016 (targets/1,000,000 m3

/time period).

Altitude

Band Dawn Day Dusk Night

50 0.0 0.0 0.0 0.0

100 0.3 0.2 0.1 0.9

150 0.4 0.3 0.4 2.1

200 0.3 0.2 0.5 2.1

250 0.3 0.2 0.3 1.9

300 0.2 0.2 0.2 1.7

350 0.3 0.1 0.1 1.4

400 0.2 0.1 0.1 1.3

450 0.2 0.1 0.1 1.1

500 0.2 0.1 0.0 1.0

550 0.2 0.0 0.0 0.8

600 0.1 0.0 0.0 0.7

650 0.1 0.0 0.0 0.6

700 0.1 0.0 0.0 0.6

750 0.1 0.0 0.0 0.5

800 0.1 0.0 0.0 0.4

850 0.1 0.0 0.0 0.4

900 0.1 0.0 0.0 0.3

950 0.0 0.0 0.0 0.3

1000 0.0 0.0 0.0 0.2

Estimated density of targets by altitude band during 

spring biological time periods (dawn, day, dusk, 

night) in Alcona County, spring 2016 (targets/

1,000,000 m3

/time period).

Altitude

Band Dawn Day Dusk Night

50 0.0 0.0 0.0

100 0.8 0.6 0.4 1.6

150 1.0 0.5 0.5 3.5

200 0.8 0.3 0.3 3.6

250 0.7 0.3 0.2 3.4

300 0.9 0.2 0.1 2.9

350 0.9 0.3 0.1 2.8

400 0.9 0.2 0.1 2.2

450 0.7 0.2 0.0 1.9

500 0.7 0.1 0.0 1.7

550 0.7 0.1 0.0 1.5

600 0.6 0.1 0.0 1.3

650 0.5 0.1 0.0 1.1

700 0.4 0.1 0.0 1.0

750 0.4 0.0 0.0 0.9

800 0.3 0.0 0.0 0.8

850 0.3 0.0 0.0 0.6

900 0.2 0.0 0.0 0.5

950 0.2 0.0 0.0 0.5

1000 0.1 0.0 0.0 0.4

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Appendix 4

Comparison of Static and Corrected Density Estimates

Comparison of methods to estimate target density by altitude band during the 

dawn biological period in Presque Isle County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 8 8 31.3 5.6 0.0 0.0 0.2% 0.2% 0.3%

100 154 162 31.3 5.9 0.1 0.3 3.0% 3.0% 5.6%

150 308 470 31.3 6.5 0.1 0.6 6.0% 6.0% 10.2%

200 381 851 31.3 7.1 0.2 0.7 7.4% 7.4% 11.5%

250 537 1,388 31.3 7.9 0.2 0.9 10.4% 10.4% 14.6%

300 539 1,927 31.3 8.5 0.2 0.9 10.4% 10.4% 13.6%

350 358 2,285 31.3 9.5 0.2 0.5 6.9% 6.9% 8.1%

400 293 2,578 31.3 10.3 0.1 0.4 5.7% 5.7% 6.1%

450 252 2,830 31.3 11.2 0.1 0.3 4.9% 4.9% 4.8%

500 221 3,051 31.3 12.2 0.1 0.2 4.3% 4.3% 3.9%

550 196 3,247 31.3 13.3 0.1 0.2 3.8% 3.8% 3.2%

600 168 3,415 31.3 14.1 0.1 0.2 3.3% 3.3% 2.5%

650 132 3,547 31.3 15.3 0.1 0.1 2.6% 2.6% 1.8%

700 137 3,684 31.3 16.2 0.1 0.1 2.7% 2.7% 1.8%

750 118 3,802 31.3 17.2 0.1 0.1 2.3% 2.3% 1.5%

800 97 3,899 31.3 18.2 0.0 0.1 1.9% 1.9% 1.1%

850 93 3,992 31.3 19.4 0.0 0.1 1.8% 1.8% 1.0%

900 76 4,068 31.3 20.4 0.0 0.1 1.5% 1.5% 0.8%

950 66 4,134 31.3 21.4 0.0 0.0 1.3% 1.3% 0.7%

1000 52 4,186 31.3 22.4 0.0 0.0 1.0% 1.0% 0.5%

1 Total target counts recorded up to 2,800 m band during the dawn time period was 5,158.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 6.28.

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Comparison of methods to estimate target density by altitude band during the day 

biological period in Presque Isle County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 42 42 31.3 5.6 0.0 0.0 0.3% 0.3% 0.4%

100 929 971 31.3 5.9 0.0 0.2 5.6% 5.6% 8.8%

150 1,148 2,119 31.3 6.5 0.0 0.2 7.0% 7.0% 10.0%

200 1,738 3,857 31.3 7.1 0.1 0.3 10.6% 10.6% 13.8%

250 2,143 6,000 31.3 7.9 0.1 0.3 13.0% 13.0% 15.2%

300 2,528 8,528 31.3 8.5 0.1 0.3 15.4% 15.4% 16.7%

350 1,536 10,064 31.3 9.5 0.1 0.2 9.3% 9.3% 9.1%

400 1,321 11,385 31.3 10.3 0.0 0.1 8.0% 8.0% 7.2%

450 971 12,356 31.3 11.2 0.0 0.1 5.9% 5.9% 4.9%

500 788 13,144 31.3 12.2 0.0 0.1 4.8% 4.8% 3.6%

550 632 13,776 31.3 13.3 0.0 0.1 3.8% 3.8% 2.7%

600 459 14,235 31.3 14.1 0.0 0.0 2.8% 2.8% 1.8%

650 307 14,542 31.3 15.3 0.0 0.0 1.9% 1.9% 1.1%

700 245 14,787 31.3 16.2 0.0 0.0 1.5% 1.5% 0.8%

750 209 14,996 31.3 17.2 0.0 0.0 1.3% 1.3% 0.7%

800 166 15,162 31.3 18.2 0.0 0.0 1.0% 1.0% 0.5%

850 130 15,292 31.3 19.4 0.0 0.0 0.8% 0.8% 0.4%

900 103 15,395 31.3 20.4 0.0 0.0 0.6% 0.6% 0.3%

950 68 15,463 31.3 21.4 0.0 0.0 0.4% 0.4% 0.2%

1000 70 15,533 31.3 22.4 0.0 0.0 0.4% 0.4% 0.2%

1 Total target counts recorded up to 2,800 m band during the day time period was 16,446.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 2.07.

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Comparison of methods to estimate target density by altitude band during the 

dusk biological period in Presque Isle County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 1 1 31.3 5.6 0.0 0.0 0.0% 0.0% 0.1%

100 128 129 31.3 5.9 0.1 0.3 5.9% 5.9% 8.1%

150 347 476 31.3 6.5 0.2 0.8 15.9% 15.9% 20.3%

200 362 838 31.3 7.1 0.2 0.7 16.6% 16.6% 19.3%

250 348 1,186 31.3 7.9 0.2 0.6 16.0% 16.0% 16.6%

300 356 1,542 31.3 8.5 0.2 0.6 16.3% 16.3% 15.8%

350 204 1,746 31.3 9.5 0.1 0.3 9.4% 9.4% 8.1%

400 124 1,870 31.3 10.3 0.1 0.2 5.7% 5.7% 4.5%

450 70 1,940 31.3 11.2 0.0 0.1 3.2% 3.2% 2.4%

500 50 1,990 31.3 12.2 0.0 0.1 2.3% 2.3% 1.5%

550 20 2,010 31.3 13.3 0.0 0.0 0.9% 0.9% 0.6%

600 20 2,030 31.3 14.1 0.0 0.0 0.9% 0.9% 0.5%

650 27 2,057 31.3 15.3 0.0 0.0 1.2% 1.2% 0.7%

700 5 2,062 31.3 16.2 0.0 0.0 0.2% 0.2% 0.1%

750 7 2,069 31.3 17.2 0.0 0.0 0.3% 0.3% 0.2%

800 1 2,070 31.3 18.2 0.0 0.0 0.0% 0.0% 0.0%

850 2 2,072 31.3 19.4 0.0 0.0 0.1% 0.1% 0.0%

900 2 2,074 31.3 20.4 0.0 0.0 0.1% 0.1% 0.0%

950 1 2,075 31.3 21.4 0.0 0.0 0.0% 0.0% 0.0%

1000 4 2,079 31.3 22.4 0.0 0.0 0.2% 0.2% 0.1%

1 Total target counts recorded up to 2,800 m band during the dusk time period was 2,181.

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Comparison of methods to estimate target density by altitude band during the 

night biological period in Presque Isle County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 69 69 31.3 5.6 0.0 0.0 0.0% 0.0% 0.0%

100 7,026 7,095 31.3 5.9 0.3 1.6 2.7% 2.7% 4.7%

150 22,402 29,497 31.3 6.5 1.0 4.6 8.5% 8.5% 13.8%

200 23,950 53,447 31.3 7.1 1.0 4.5 9.1% 9.1% 13.5%

250 24,761 78,208 31.3 7.9 1.1 4.2 9.4% 9.4% 12.5%

300 24,762 102,970 31.3 8.5 1.1 3.9 9.4% 9.4% 11.6%

350 19,593 122,563 31.3 9.5 0.8 2.7 7.4% 7.4% 8.3%

400 16,850 139,413 31.3 10.3 0.7 2.2 6.4% 6.4% 6.5%

450 14,367 153,780 31.3 11.2 0.6 1.7 5.5% 5.5% 5.1%

500 12,411 166,191 31.3 12.2 0.5 1.3 4.7% 4.7% 4.1%

550 10,875 177,066 31.3 13.3 0.5 1.1 4.1% 4.1% 3.3%

600 9,587 186,653 31.3 14.1 0.4 0.9 3.6% 3.6% 2.7%

650 8,591 195,244 31.3 15.3 0.4 0.7 3.3% 3.3% 2.2%

700 7,544 202,788 31.3 16.2 0.3 0.6 2.9% 2.9% 1.9%

750 6,440 209,228 31.3 17.2 0.3 0.5 2.4% 2.4% 1.5%

800 5,738 214,966 31.3 18.2 0.2 0.4 2.2% 2.2% 1.3%

850 4,708 219,674 31.3 19.4 0.2 0.3 1.8% 1.8% 1.0%

900 3,963 223,637 31.3 20.4 0.2 0.3 1.5% 1.5% 0.8%

950 3,091 226,728 31.3 21.4 0.1 0.2 1.2% 1.2% 0.6%

1000 2,620 229,348 31.3 22.4 0.1 0.2 1.0% 1.0% 0.5%

1 Total target counts recorded up to 2,800 m band during the night time period was 263,613.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 33.23.

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Comparison of methods to estimate target density by altitude band during the 

dawn biological period in Alcona County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 5 5 31.3 5.6 0.0 0.0 0.1% 0.1% 0.2%

100 227 232 31.3 5.9 0.1 0.5 3.5% 3.5% 7.1%

150 323 555 31.3 6.5 0.1 0.7 4.9% 4.9% 9.3%

200 313 868 31.3 7.1 0.1 0.6 4.8% 4.8% 8.2%

250 301 1,169 31.3 7.9 0.1 0.5 4.6% 4.6% 7.1%

300 340 1,509 31.3 8.5 0.1 0.5 5.2% 5.2% 7.4%

350 544 2,053 31.3 9.5 0.2 0.8 8.3% 8.3% 10.7%

400 491 2,544 31.3 10.3 0.2 0.6 7.5% 7.5% 8.9%

450 429 2,973 31.3 11.2 0.2 0.5 6.6% 6.6% 7.1%

500 387 3,360 31.3 12.2 0.2 0.4 5.9% 5.9% 5.9%

550 315 3,675 31.3 13.3 0.1 0.3 4.8% 4.8% 4.4%

600 294 3,969 31.3 14.1 0.1 0.3 4.5% 4.5% 3.9%

650 191 4,160 31.3 15.3 0.1 0.2 2.9% 2.9% 2.3%

700 205 4,365 31.3 16.2 0.1 0.2 3.1% 3.1% 2.4%

750 185 4,550 31.3 17.2 0.1 0.1 2.8% 2.8% 2.0%

800 159 4,709 31.3 18.2 0.1 0.1 2.4% 2.4% 1.6%

850 131 4,840 31.3 19.4 0.1 0.1 2.0% 2.0% 1.3%

900 107 4,947 31.3 20.4 0.0 0.1 1.6% 1.6% 1.0%

950 128 5,075 31.3 21.4 0.1 0.1 2.0% 2.0% 1.1%

1000 91 5,166 31.3 22.4 0.0 0.1 1.4% 1.4% 0.8%

1 Total target counts recorded up to 2,800 m band during the dawn time period was 6,526.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 7.10.

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Comparison of methods to estimate target density by altitude band during the day 

biological period in Alcona County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 40 40 31.3 5.6 0.0 0.0 0.3% 0.3% 0.5%

100 933 973 31.3 5.9 0.0 0.2 6.0% 6.0% 10.0%

150 1,115 2,088 31.3 6.5 0.0 0.2 7.2% 7.2% 11.0%

200 1,202 3,290 31.3 7.1 0.0 0.2 7.8% 7.8% 10.8%

250 1,392 4,682 31.3 7.9 0.1 0.2 9.0% 9.0% 11.3%

300 1,218 5,900 31.3 8.5 0.0 0.2 7.9% 7.9% 9.2%

350 2,167 8,067 31.3 9.5 0.1 0.3 14.0% 14.0% 14.6%

400 1,649 9,716 31.3 10.3 0.1 0.2 10.7% 10.7% 10.2%

450 1,079 10,795 31.3 11.2 0.0 0.1 7.0% 7.0% 6.1%

500 732 11,527 31.3 12.2 0.0 0.1 4.7% 4.7% 3.8%

550 511 12,038 31.3 13.3 0.0 0.0 3.3% 3.3% 2.5%

600 407 12,445 31.3 14.1 0.0 0.0 2.6% 2.6% 1.8%

650 306 12,751 31.3 15.3 0.0 0.0 2.0% 2.0% 1.3%

700 248 12,999 31.3 16.2 0.0 0.0 1.6% 1.6% 1.0%

750 230 13,229 31.3 17.2 0.0 0.0 1.5% 1.5% 0.9%

800 165 13,394 31.3 18.2 0.0 0.0 1.1% 1.1% 0.6%

850 144 13,538 31.3 19.4 0.0 0.0 0.9% 0.9% 0.5%

900 126 13,664 31.3 20.4 0.0 0.0 0.8% 0.8% 0.4%

950 99 13,763 31.3 21.4 0.0 0.0 0.6% 0.6% 0.3%

1000 102 13,865 31.3 22.4 0.0 0.0 0.7% 0.7% 0.3%

1 Total target counts recorded up to 2,800 m band during the day time period was 1,542.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 1.83.

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Comparison of methods to estimate target density by altitude band during the 

dusk biological period in Alcona County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 2 2 31.3 5.6 0.0 0.0 0.1% 0.1% 0.1%

100 121 123 31.3 5.9 0.1 0.3 4.5% 4.5% 6.7%

150 315 438 31.3 6.5 0.1 0.7 11.8% 11.8% 16.0%

200 366 804 31.3 7.1 0.2 0.7 13.7% 13.7% 17.0%

250 422 1,226 31.3 7.9 0.2 0.7 15.8% 15.8% 17.6%

300 290 1,516 31.3 8.5 0.1 0.5 10.9% 10.9% 11.2%

350 372 1,888 31.3 9.5 0.2 0.5 13.9% 13.9% 12.9%

400 211 2,099 31.3 10.3 0.1 0.3 7.9% 7.9% 6.7%

450 126 2,225 31.3 11.2 0.1 0.2 4.7% 4.7% 3.7%

500 85 2,310 31.3 12.2 0.0 0.1 3.2% 3.2% 2.3%

550 54 2,364 31.3 13.3 0.0 0.1 2.0% 2.0% 1.3%

600 37 2,401 31.3 14.1 0.0 0.0 1.4% 1.4% 0.9%

650 23 2,424 31.3 15.3 0.0 0.0 0.9% 0.9% 0.5%

700 25 2,449 31.3 16.2 0.0 0.0 0.9% 0.9% 0.5%

750 15 2,464 31.3 17.2 0.0 0.0 0.6% 0.6% 0.3%

800 12 2,476 31.3 18.2 0.0 0.0 0.4% 0.4% 0.2%

850 10 2,486 31.3 19.4 0.0 0.0 0.4% 0.4% 0.2%

900 17 2,503 31.3 20.4 0.0 0.0 0.6% 0.6% 0.3%

950 3 2,506 31.3 21.4 0.0 0.0 0.1% 0.1% 0.0%

1000 8 2,514 31.3 22.4 0.0 0.0 0.3% 0.3% 0.1%

1 Total target counts recorded up to 2,800 m band during the dusk time period was 2,668.

2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 4.12.

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Comparison of methods to estimate target density by altitude band during the night 

biological period in Alcona County, fall 2015.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 14 14 31.3 5.6 0.0 0.0 0.0% 0.0% 0.0%

100 7,119 7,133 31.3 5.9 0.3 1.5 2.0% 2.0% 4.2%

150 17,945 25,078 31.3 6.5 0.7 3.4 5.1% 5.1% 9.8%

200 19,158 44,236 31.3 7.1 0.8 3.4 5.4% 5.4% 9.5%

250 21,010 65,246 31.3 7.9 0.8 3.3 5.9% 5.9% 9.3%

300 18,893 84,139 31.3 8.5 0.7 2.8 5.3% 5.3% 7.8%

350 23,950 108,089 31.3 9.5 1.0 3.1 6.8% 6.8% 8.9%

400 21,211 129,300 31.3 10.3 0.8 2.5 6.0% 6.0% 7.2%

450 18,851 148,151 31.3 11.2 0.7 2.1 5.3% 5.3% 5.9%

500 17,809 165,960 31.3 12.2 0.7 1.8 5.0% 5.0% 5.1%

550 16,385 182,345 31.3 13.3 0.7 1.5 4.6% 4.6% 4.3%

600 15,337 197,682 31.3 14.1 0.6 1.3 4.3% 4.3% 3.8%

650 14,215 211,897 31.3 15.3 0.6 1.2 4.0% 4.0% 3.3%

700 12,731 224,628 31.3 16.2 0.5 1.0 3.6% 3.6% 2.8%

750 11,975 236,603 31.3 17.2 0.5 0.9 3.4% 3.4% 2.4%

800 10,779 247,382 31.3 18.2 0.4 0.7 3.0% 3.0% 2.1%

850 9,477 256,859 31.3 19.4 0.4 0.6 2.7% 2.7% 1.7%

900 8,552 265,411 31.3 20.4 0.3 0.5 2.4% 2.4% 1.5%

950 7,450 272,861 31.3 21.4 0.3 0.4 2.1% 2.1% 1.2%

1000 6,556 279,417 31.3 22.4 0.3 0.4 1.9% 1.9% 1.0%

1 Total target counts recorded up to 2,800 m band during the night time period was 353,586.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 35.29.

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Comparison of methods to estimate target density by altitude band during the dawn biological period 

in Presque Isle County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 2 2 31.3 5.6 0.00 0.0 0.0% 0.0% 0.1%

100 181 183 31.3 5.9 0.05 0.3 3.2% 3.2% 7.0%

150 323 506 31.3 6.5 0.09 0.4 5.7% 5.7% 11.5%

200 260 766 31.3 7.1 0.07 0.3 4.6% 4.6% 8.4%

250 240 1,006 31.3 7.9 0.06 0.3 4.2% 4.2% 7.0%

300 229 1,235 31.3 8.5 0.06 0.2 4.0% 4.0% 6.2%

350 282 1,517 31.3 9.5 0.08 0.3 4.9% 4.9% 6.9%

400 290 1,807 31.3 10.3 0.08 0.2 5.1% 5.1% 6.5%

450 315 2,122 31.3 11.2 0.08 0.2 5.5% 5.5% 6.5%

500 249 2,371 31.3 12.2 0.07 0.2 4.4% 4.4% 4.7%

550 264 2,635 31.3 13.3 0.07 0.2 4.6% 4.6% 4.6%

600 239 2,874 31.3 14.1 0.06 0.1 4.2% 4.2% 3.9%

650 221 3,095 31.3 15.3 0.06 0.1 3.9% 3.9% 3.3%

700 203 3,298 31.3 16.2 0.05 0.1 3.6% 3.6% 2.9%

750 198 3,496 31.3 17.2 0.05 0.1 3.5% 3.5% 2.7%

800 149 3,645 31.3 18.2 0.04 0.1 2.6% 2.6% 1.9%

850 162 3,807 31.3 19.4 0.04 0.1 2.8% 2.8% 1.9%

900 139 3,946 31.3 20.4 0.04 0.1 2.4% 2.4% 1.6%

950 105 4,051 31.3 21.4 0.03 0.0 1.8% 1.8% 1.1%

1000 71 4,122 31.3 22.4 0.02 0.0 1.2% 1.2% 0.7%

1 Total target counts recorded up to 2,800 m band during the dawn time period was 5,697.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 3.65.

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Comparison of methods to estimate target density by altitude band during the day 

biological period in Presque Isle County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 32 32 31.3 5.6 0.0 0.0 0.1% 0.1% 0.2%

100 1,918 1,950 31.3 5.9 0.0 0.2 7.5% 7.5% 12.0%

150 2,657 4,607 31.3 6.5 0.1 0.3 10.5% 10.5% 15.3%

200 2,403 7,010 31.3 7.1 0.0 0.2 9.5% 9.5% 12.6%

250 2,551 9,561 31.3 7.9 0.1 0.2 10.0% 10.0% 12.0%

300 2,519 12,080 31.3 8.5 0.1 0.2 9.9% 9.9% 11.1%

350 2,155 14,235 31.3 9.5 0.0 0.1 8.5% 8.5% 8.5%

400 1,963 16,198 31.3 10.3 0.0 0.1 7.7% 7.7% 7.1%

450 1,415 17,613 31.3 11.2 0.0 0.1 5.6% 5.6% 4.7%

500 1,160 18,773 31.3 12.2 0.0 0.1 4.6% 4.6% 3.5%

550 916 19,689 31.3 13.3 0.0 0.0 3.6% 3.6% 2.6%

600 693 20,382 31.3 14.1 0.0 0.0 2.7% 2.7% 1.8%

650 581 20,963 31.3 15.3 0.0 0.0 2.3% 2.3% 1.4%

700 574 21,537 31.3 16.2 0.0 0.0 2.3% 2.3% 1.3%

750 449 21,986 31.3 17.2 0.0 0.0 1.8% 1.8% 1.0%

800 314 22,300 31.3 18.2 0.0 0.0 1.2% 1.2% 0.6%

850 266 22,566 31.3 19.4 0.0 0.0 1.0% 1.0% 0.5%

900 240 22,806 31.3 20.4 0.0 0.0 0.9% 0.9% 0.4%

950 198 23,004 31.3 21.4 0.0 0.0 0.8% 0.8% 0.3%

1000 159 23,163 31.3 22.4 0.0 0.0 0.6% 0.6% 0.3%

1 Total target counts recorded up to 2,800 m band during the day time period was 25,425.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 1.67.

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Comparison of methods to estimate target density by altitude band during the 

dusk biological period in Presque Isle County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 1 1 31.3 5.6 0.0 0.0 0.0% 0.0% 0.1%

100 92 93 31.3 5.9 0.0 0.1 4.5% 4.5% 6.7%

150 285 378 31.3 6.5 0.1 0.4 13.8% 13.8% 18.9%

200 396 774 31.3 7.1 0.1 0.5 19.2% 19.2% 24.0%

250 295 1,069 31.3 7.9 0.1 0.3 14.3% 14.3% 16.0%

300 198 1,267 31.3 8.5 0.1 0.2 9.6% 9.6% 10.0%

350 137 1,404 31.3 9.5 0.0 0.1 6.6% 6.6% 6.2%

400 106 1,510 31.3 10.3 0.0 0.1 5.1% 5.1% 4.4%

450 73 1,583 31.3 11.2 0.0 0.1 3.5% 3.5% 2.8%

500 54 1,637 31.3 12.2 0.0 0.0 2.6% 2.6% 1.9%

550 37 1,674 31.3 13.3 0.0 0.0 1.8% 1.8% 1.2%

600 40 1,714 31.3 14.1 0.0 0.0 1.9% 1.9% 1.2%

650 40 1,754 31.3 15.3 0.0 0.0 1.9% 1.9% 1.1%

700 28 1,782 31.3 16.2 0.0 0.0 1.4% 1.4% 0.7%

750 18 1,800 31.3 17.2 0.0 0.0 0.9% 0.9% 0.4%

800 17 1,817 31.3 18.2 0.0 0.0 0.8% 0.8% 0.4%

850 19 1,836 31.3 19.4 0.0 0.0 0.9% 0.9% 0.4%

900 20 1,856 31.3 20.4 0.0 0.0 1.0% 1.0% 0.4%

950 12 1,868 31.3 21.4 0.0 0.0 0.6% 0.6% 0.2%

1000 22 1,890 31.3 22.4 0.0 0.0 1.1% 1.1% 0.4%

1 Total target counts recorded up to 2,800 m band during the dusk time period was 2,065.

2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 1.95.

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Comparison of methods to estimate target density by altitude band during the 

night biological period in Presque Isle County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 18 18 31.3 5.6 0.0 0.0 0.0% 0.0% 0.0%

100 5,383 5,401 31.3 5.9 0.2 0.9 1.9% 1.9% 4.3%

150 14,085 19,486 31.3 6.5 0.4 2.1 5.0% 5.0% 10.3%

200 14,835 34,321 31.3 7.1 0.5 2.1 5.3% 5.3% 9.9%

250 14,937 49,258 31.3 7.9 0.5 1.9 5.3% 5.3% 9.0%

300 14,865 64,123 31.3 8.5 0.5 1.7 5.3% 5.3% 8.3%

350 13,756 77,879 31.3 9.5 0.4 1.4 4.9% 4.9% 6.9%

400 13,509 91,388 31.3 10.3 0.4 1.3 4.8% 4.8% 6.2%

450 12,549 103,937 31.3 11.2 0.4 1.1 4.5% 4.5% 5.3%

500 11,899 115,836 31.3 12.2 0.4 1.0 4.2% 4.2% 4.6%

550 11,044 126,880 31.3 13.3 0.3 0.8 3.9% 3.9% 3.9%

600 10,613 137,493 31.3 14.1 0.3 0.7 3.8% 3.8% 3.6%

650 9,592 147,085 31.3 15.3 0.3 0.6 3.4% 3.4% 3.0%

700 9,405 156,490 31.3 16.2 0.3 0.6 3.3% 3.3% 2.7%

750 8,779 165,269 31.3 17.2 0.3 0.5 3.1% 3.1% 2.4%

800 7,953 173,222 31.3 18.2 0.3 0.4 2.8% 2.8% 2.1%

850 7,407 180,629 31.3 19.4 0.2 0.4 2.6% 2.6% 1.8%

900 6,648 187,277 31.3 20.4 0.2 0.3 2.4% 2.4% 1.5%

950 5,965 193,242 31.3 21.4 0.2 0.3 2.1% 2.1% 1.3%

1000 5,031 198,273 31.3 22.4 0.2 0.2 1.8% 1.8% 1.1%

1 Total target counts recorded up to 2,800 m band during the night time period was 281,577.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 20.76.

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Comparison of methods to estimate target density by altitude band during the 

dawn biological period in Alcona County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 4 4 31.3 5.6 0.0 0.0 0.0% 0.0% 0.1%

100 313 317 31.3 5.9 0.1 0.8 2.9% 2.9% 6.4%

150 415 732 31.3 6.5 0.2 1.0 3.8% 3.8% 7.8%

200 361 1,093 31.3 7.1 0.2 0.8 3.3% 3.3% 6.2%

250 396 1,489 31.3 7.9 0.2 0.7 3.6% 3.6% 6.1%

300 489 1,978 31.3 8.5 0.2 0.9 4.5% 4.5% 7.0%

350 564 2,542 31.3 9.5 0.3 0.9 5.1% 5.1% 7.3%

400 606 3,148 31.3 10.3 0.3 0.9 5.5% 5.5% 7.2%

450 538 3,686 31.3 11.2 0.3 0.7 4.9% 4.9% 5.9%

500 560 4,246 31.3 12.2 0.3 0.7 5.1% 5.1% 5.6%

550 590 4,836 31.3 13.3 0.3 0.7 5.4% 5.4% 5.4%

600 554 5,390 31.3 14.1 0.3 0.6 5.0% 5.0% 4.8%

650 544 5,934 31.3 15.3 0.3 0.5 5.0% 5.0% 4.3%

700 484 6,418 31.3 16.2 0.2 0.4 4.4% 4.4% 3.6%

750 424 6,842 31.3 17.2 0.2 0.4 3.9% 3.9% 3.0%

800 413 7,255 31.3 18.2 0.2 0.3 3.8% 3.8% 2.8%

850 346 7,601 31.3 19.4 0.2 0.3 3.2% 3.2% 2.2%

900 268 7,869 31.3 20.4 0.1 0.2 2.4% 2.4% 1.6%

950 238 8,107 31.3 21.4 0.1 0.2 2.2% 2.2% 1.4%

1000 222 8,329 31.3 22.4 0.1 0.1 2.0% 2.0% 1.2%

1 Total target counts recorded up to 2,800 m band during the dawn time period was 10,972.

2 Total density of targets per hour recorded up to the 2,800 m band during the dawn time period was 12.16.

Avian Report.indd 95 7/24/18 6:2
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Comparison of methods to estimate target density by altitude band during the 

day biological period in Alcona County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 41 41 31.3 5.6 0.0 0.0 0.1% 0.1% 0.3%

100 3,005 3,046 31.3 5.9 0.1 0.6 10.6% 10.6% 18.1%

150 2,667 5,713 31.3 6.5 0.1 0.5 9.4% 9.4% 14.8%

200 1,882 7,595 31.3 7.1 0.1 0.3 6.6% 6.6% 9.5%

250 1,810 9,405 31.3 7.9 0.1 0.3 6.4% 6.4% 8.2%

300 1,539 10,944 31.3 8.5 0.1 0.2 5.4% 5.4% 6.5%

350 2,264 13,208 31.3 9.5 0.1 0.3 8.0% 8.0% 8.6%

400 1,896 15,104 31.3 10.3 0.1 0.2 6.7% 6.7% 6.6%

450 1,497 16,601 31.3 11.2 0.1 0.2 5.3% 5.3% 4.8%

500 1,374 17,975 31.3 12.2 0.1 0.1 4.8% 4.8% 4.0%

550 1,175 19,150 31.3 13.3 0.0 0.1 4.1% 4.1% 3.2%

600 1,056 20,206 31.3 14.1 0.0 0.1 3.7% 3.7% 2.7%

650 894 21,100 31.3 15.3 0.0 0.1 3.1% 3.1% 2.1%

700 737 21,837 31.3 16.2 0.0 0.1 2.6% 2.6% 1.6%

750 633 22,470 31.3 17.2 0.0 0.0 2.2% 2.2% 1.3%

800 547 23,017 31.3 18.2 0.0 0.0 1.9% 1.9% 1.1%

850 516 23,533 31.3 19.4 0.0 0.0 1.8% 1.8% 1.0%

900 449 23,982 31.3 20.4 0.0 0.0 1.6% 1.6% 0.8%

950 331 24,313 31.3 21.4 0.0 0.0 1.2% 1.2% 0.6%

1000 264 24,577 31.3 22.4 0.0 0.0 0.9% 0.9% 0.4%

1 Total target counts recorded up to 2,800 m band during the day time period was 28,472.

2 Total density of targets per hour recorded up to the 2,800 m band during the day time period was 3.24.

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Great Lakes Avian Radar Technical Report Lake Huron Shoreline 87

Comparison of methods to estimate target density by altitude band during the 

dusk biological period in Alcona County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 0 31.3 5.6 0.0% 0.0% 0.0%

100 147 147 31.3 5.9 0.1 0.4 16.2% 16.2% 21.9%

150 214 361 31.3 6.5 0.1 0.5 23.6% 23.6% 29.3%

200 152 513 31.3 7.1 0.1 0.3 16.8% 16.8% 18.9%

250 80 593 31.3 7.9 0.0 0.2 8.8% 8.8% 8.9%

300 47 640 31.3 8.5 0.0 0.1 5.2% 5.2% 4.9%

350 44 684 31.3 9.5 0.0 0.1 4.9% 4.9% 4.1%

400 42 726 31.3 10.3 0.0 0.1 4.6% 4.6% 3.6%

450 25 751 31.3 11.2 0.0 0.0 2.8% 2.8% 2.0%

500 12 763 31.3 12.2 0.0 0.0 1.3% 1.3% 0.9%

550 14 777 31.3 13.3 0.0 0.0 1.5% 1.5% 0.9%

600 9 786 31.3 14.1 0.0 0.0 1.0% 1.0% 0.6%

650 14 800 31.3 15.3 0.0 0.0 1.5% 1.5% 0.8%

700 8 808 31.3 16.2 0.0 0.0 0.9% 0.9% 0.4%

750 2 810 31.3 17.2 0.0 0.0 0.2% 0.2% 0.1%

800 3 813 31.3 18.2 0.0 0.0 0.3% 0.3% 0.1%

850 8 821 31.3 19.4 0.0 0.0 0.9% 0.9% 0.4%

900 4 825 31.3 20.4 0.0 0.0 0.4% 0.4% 0.2%

950 4 829 31.3 21.4 0.0 0.0 0.4% 0.4% 0.2%

1000 1 830 31.3 22.4 0.0 0.0 0.1% 0.1% 0.0%

1 Total target counts recorded up to 2,800 m band during the dusk time period was 906.

2 Total density of targets per hour recorded up to the 2,800 m band during the dusk time period was 1.76.

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88 Great Lakes Avian Radar Technical Report Lake Huron Shoreline

Comparison of methods to estimate target density by altitude band during the 

night biological period in Alcona County, spring 2016.

 Running Static Corrected

 Total Target Target %

Altitude Target Target Static Corrected Density Density % Total % Static Corrected

Band (m) Count Count1 Volume Volume per Hour per Hour2 Targets Density Density

50 13 13 31.3 5.6 0.0 0.0 0.0% 0.0% 0.0%

100 5,359 5,372 31.3 5.9 0.3 1.6 2.1% 2.1% 4.6%

150 12,493 17,865 31.3 6.5 0.7 3.5 4.9% 4.9% 9.8%

200 13,961 31,826 31.3 7.1 0.8 3.6 5.5% 5.5% 10.0%

250 14,852 46,678 31.3 7.9 0.9 3.4 5.8% 5.8% 9.5%

300 13,676 60,354 31.3 8.5 0.8 2.9 5.4% 5.4% 8.1%

350 14,436 74,790 31.3 9.5 0.8 2.8 5.7% 5.7% 7.7%

400 12,773 87,563 31.3 10.3 0.7 2.2 5.0% 5.0% 6.3%

450 11,839 99,402 31.3 11.2 0.7 1.9 4.7% 4.7% 5.3%

500 11,437 110,839 31.3 12.2 0.7 1.7 4.5% 4.5% 4.7%

550 10,814 121,653 31.3 13.3 0.6 1.5 4.3% 4.3% 4.1%

600 10,174 131,827 31.3 14.1 0.6 1.3 4.0% 4.0% 3.6%

650 9,553 141,380 31.3 15.3 0.6 1.1 3.8% 3.8% 3.2%

700 9,069 150,449 31.3 16.2 0.5 1.0 3.6% 3.6% 2.8%

750 8,447 158,896 31.3 17.2 0.5 0.9 3.3% 3.3% 2.5%

800 7,753 166,649 31.3 18.2 0.4 0.8 3.0% 3.0% 2.2%

850 6,704 173,353 31.3 19.4 0.4 0.6 2.6% 2.6% 1.7%

900 6,157 179,510 31.3 20.4 0.4 0.5 2.4% 2.4% 1.5%

950 5,461 184,971 31.3 21.4 0.3 0.5 2.1% 2.1% 1.3%

1000 4,644 189,615 31.3 22.4 0.3 0.4 1.8% 1.8% 1.0%

1 Total target counts recorded up to 2,800 m band during the night time period was 254,368.

2 Total density of targets per hour recorded up to the 2,800 m band during the night time period was 35.71.

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Department of the Interior

U.S. Fish and Wildlife Service

Fall 2015 & Spring 2016

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