Demographics and Movements of Least Terns and Piping 

Plovers in the Central Platte River Valley, Nebraska

Open-File Report 2016–1061

U.S. Department of the Interior

U.S. Geological Survey

Demographics and Movements of Least 

Terns and Piping Plovers in the Central 

Platte River Valley, Nebraska

By Erin A. Roche, Mark H. Sherfy, Megan M. Ring, Terry L. Shaffer, 

Michael J. Anteau, and Jennifer H. Stucker

Open-File Report 2016–1061

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Roche, E.A., Sherfy, M.H., Ring, M.M., Shaffer, T.L., Anteau, M.J., and Stucker, J.H., 2016, Demographics and 

movements of least terns and piping plovers in the Central Platte River Valley, Nebraska: U.S. Geological Survey Open-File Report 2016–1061, 27 p., http://dx.doi.org/10.3133/ofr20161061.

ISSN 2331-1258 (online)
iii

Contents

Executive Summary.......................................................................................................................................1

Introduction.....................................................................................................................................................2

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

Methods...........................................................................................................................................................5

Field Methods........................................................................................................................................5

Data Analysis.........................................................................................................................................5

Reproductive Success—Nest Survival Rates ........................................................................5

Reproductive Success—Chick Survival to Fledging Age.....................................................6

Colonization...................................................................................................................................7

Apparent Survival of Juveniles and Nesting Adults ..............................................................7

Dispersal and Philopatry ............................................................................................................8

Renesting.......................................................................................................................................8

Migratory, Winter, and other non-Central Platte River Valley Resightings of 

Piping Plovers .................................................................................................................8

Results .............................................................................................................................................................9

Reproductive Success—Nest Survival Rates .................................................................................9

Reproductive Success—Chick Survival to Fledging Age..............................................................9

Colonization............................................................................................................................................9

Apparent Survival of Juveniles and Nesting Adults .....................................................................17

Dispersal and Philopatry....................................................................................................................18

Renesting..............................................................................................................................................19

Migratory, Winter, and other non-Central Platte River Valley Resightings of 

Piping Plovers ........................................................................................................................20

Discussion.....................................................................................................................................................22

Reproductive Success.......................................................................................................................22

Colonization..........................................................................................................................................23

Apparent Survival of Juveniles and Adults ....................................................................................23

Dispersal and Philopatry....................................................................................................................23

Renesting..............................................................................................................................................24

Migratory, Winter, and other non-Central Platte River Valley Resightings of 

Piping Plovers ........................................................................................................................24

Information Needs.......................................................................................................................................24

References Cited..........................................................................................................................................25
iv

Figures

1. Map showing Central Platte River Valley study area during 2009–14 .................................3

2. Graph showing cumulative nest survival (21 days) rates of least tern nests in the

Central Platte River Valley, 2009–14.........................................................................................10

3. Graph showing cumulative nest survival rates (21 days) based on nest site age

class for least tern nests initiated in the Central Platte River Valley, 2009–14.................11

4. Graph showing cumulative nest survival rates of piping plover nests (35 days) 

in the Central Platte River Valley, 2009–14..............................................................................12

5. Graph showing cumulative survival rates of least tern chicks to fledging age 

(16 days) in the Central Platte River Valley, 2009–14.............................................................14

6. Graph showing cumulative survival rates of least tern chicks to fledging age (16

days) based on site age class at which chicks were hatched in the Central Platte

River Valley, 2009–14 ..................................................................................................................15

7. Graph showing cumulative survival rates of piping plover chicks to fledging age 

(21 days) in the Central Platte River Valley, 2009–14.............................................................16

8. Map showing wintering ground observations of piping plovers uniquely marked in

the Central Platte River Valley, 2009–14..................................................................................21

Tables

1. Central Platte River Valley least tern and piping plover nesting sites included 

in analyses of reproductive success, dispersal, renesting frequency, and 

colonization....................................................................................................................................4

2. Number of successful and failed least tern nests on the Central Platte River Valley

during 2009–14 included in the nest survival analysis..........................................................10

3. Nest survival models used to estimate daily nest survival rates for least tern nests

initiated in the Central Platte River Valley during 2009–14...................................................10

4. Nest survival models used to estimate daily nest survival rates for least tern nests

initiated on created sites in the Central Platte River Valley during 2009–14 ....................11

5. Number of successful and failed piping plover nests in the Central Platte River

Valley during 2009–14 included in the nest survival analysis..............................................12

6. Nest survival models used to estimate daily nest survival rates for piping plover

nests initiated in the Central Platte River Valley during 2009–14........................................13

7. Nest survival models used to estimate daily nest survival rates or piping plover

nests initiated on sites created in the Central Platte River Valley during 2009–14..........13

8. Number of least terns and piping plovers banded by age and year in the Central

Platte River Valley (2009–14).....................................................................................................13

9. Cormack-Jolly-Seber survival models used to estimate daily survival rates for least

tern chicks hatched in the Central Platte River Valley during 2009–14 .............................14

10. Cormack-Jolly-Seber survival models used to estimate daily apparent survival

rates for piping plover chicks hatched in the Central Platte River Valley during

2009–14 .........................................................................................................................................15

11. Summary of least tern nests found at sites created in the Central Platte River Valley

during 2009–14 by site age in years (first year through fifth year) and site age class

(first year available and after first year available) used in linear and logistic

regression analyses ...................................................................................................................16
v

12. Summary of uniquely marked least terns resighted or recaptured on sites created

in the Central Platte River Valley during 2009–14 by site age in years, site age class,

and tern age class used in linear and logistic regression analyses..................................17

13. Summary of piping plover nests found at sites created in the Central Platte River

Valley during 2009–14 by site age in years and site age class used in linear and

logistic regression analyses .....................................................................................................17

14. Summary of uniquely marked piping plovers resighted or recaptured at sites

created in the Central Platte River Valley during 2009–14 by site age in years, site

age class, and plover age class used in linear and logistic regression analyses. .........18

15. Central Platte River Valley hatch sites and sites where a first nesting attempt was

observed for four uniquely identifiable least terns marked and resighted/recapture

during 2009–14.............................................................................................................................18

16. Dispersal of uniquely marked least terns in the Central Platte River Valley during

2009–14 .........................................................................................................................................19

17. Central Platte River Valley hatch sites and sites where a first nesting attempt was

observed for uniquely identifiable piping plovers marked and resighted/recapture

during 2009–14.............................................................................................................................19

18. Dispersal of uniquely marked piping plovers in the Central Platte River Valley

during 2009–14.............................................................................................................................20

19. Number of successful, failed, and unknown fate nests and renests attended by at

least one uniquely identifiable least tern in the Central Platte River Valley during

2009–14 .........................................................................................................................................20

20. Number of successful, failed, and unknown fate nests and renests attended by at

least one uniquely identifiable piping plover in the Central Platte River Valley during

2009–14 .........................................................................................................................................21

21. Breeding locations for uniquely identifiable adult piping plovers originally banded

in the Central Platte River Valley..............................................................................................22

Conversion Factors

International System of Units to Inch/Pound

Multiply By To obtain

Length

kilometer (km) 0.6214 mile (mi)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as 

°C = (°F – 32) / 1.8.
vi

Abbreviations

°C degrees Celsius

°F degrees Fahrenheit

AFY after first year

AIC Akaiki’s information criterion

AICc Akaiki’s information criterion corrected for small sample size

ĉ overdispersion

CI confidence interval

CJS Cormack-Jolly-Seber

DOD U.S. Department of Defense

EPA U.S. Environmental Protection Agency

FY first year

GPS global positioning system

k number of parameters

p detection probability

φ apparent survival probability

ppm parts per million

PRRIP Platte River Recovery Implementation Program

QAICc Quasi-Akaiki’s information criterion corrected for small sample size

S survival probability

SD South Dakota

USGS U.S. Geological Survey

UTM Universal Transverse Mercator
Demographics and Movements of Least Terns and Piping 

Plovers in the Central Platte River Valley, Nebraska

By Erin A. Roche, Mark H. Sherfy, Megan M. Ring, Terry L. Shaffer, Michael J. Anteau, and 

Jennifer H. Stucker

Executive Summary

The Central Platte River Valley provides breeding habitat 

for a variety of migratory birds, including federally endangered interior least terns (Sternula antillarum; least tern) and 

threatened piping plovers (Charadrius melodus). Since 2009, 

researchers have collected demographic data on both species 

that span their lifecycle (that is, from egg laying through survival of adults). Demographic data were used to estimate vital 

rates (for example, nest survival, chick survival, and so on) for 

both species and assess how these vital rates were related to 

type and age of nesting habitat. Nest survival of both species 

was unrelated to the age of the site a nest was initiated on. 

Piping plover chick survival to fledging age was not related to 

the age of the site it was hatched at, however, the probability 

of a least tern chick surviving to fledging was higher at older 

sites. In general there were fewer piping plover nests than least 

tern nests found at sites created through either the physical 

construction of a new site or new vegetation management 

regimes, during 2009–14.

Mean daily least tern nest survival was 0.9742 

(95-percent confidence interval [CI]: 0.9692–0.9783) and 

cumulative nest survival was 0.59 (95-percent CI: 0.53–0.65). 

Mean daily least tern chick survival was 0.9602 (95-percent 

CI: 0.9515–0.9673) and cumulative survival to fledging was 

0.54 (95-percent CI = 0.48–0.61). Annual apparent survival 

rates were estimated at 0.42 (95-percent CI = 0.22–0.64) for 

adult least terns nesting in the Central Platte River Valley and 

an apparent survival rate of 0.14 (95-pecent CI = 0.04–0.41) 

for juvenile least terns. The number of least tern nests present 

at sites created during 2009–14 was associated with the age 

of the site; more least tern nests were associated with older 

sites. During 2009–14, there were four (less than 1 percent of 

all chicks marked) least tern chicks hatched from the Central 

Platte River Valley that were subsequently captured on nests 

as adults. Two of these least terns returned to nest at the same 

site they had hatched from. Ten instances were documented 

in which an adult least tern could either switch to nest at a 

new location or remain at the previous location with the onset 

of a new year. In five (50 percent) of these instances, least 

terns returned to nest on the site where they had nested in a 

previous year.

For piping plovers, mean daily apparent nest survival 

was 0.9880 (95-pecent CI: 0.9836–0.9912) and cumulative nest survival was 0.66 (95-pecent CI: 0.57–0.74). Mean 

daily piping plover chick survival was 0.9621 (95-pecent CI: 

0.9514–0.9706) and cumulative survival to fledging was 0.46 

(95-pecent CI = 0.37– 0.56). The annual apparent survival 

estimate for adult piping plovers nesting in the Central Platte 

River Valley was 0.76 (95-pecent CI = 0.65–0.85) and was 

0.20 (95-pecent CI = 0.14–0.29) for juvenile piping plovers. 

The number of piping plover nests present at sites created 

through either the physical construction of a new site or new 

vegetation management regimes was also associated with 

site age, with more piping plover nests associated with older 

sites; however, in general there were fewer piping plover nests 

found at created sites than least tern nests. Only first-year 

adult piping plovers were observed on sites in the first year 

of availability, whereas older sites had a higher proportion of 

after-first-year adult piping plovers than first-year adult piping 

plovers. Twelve piping plover chicks (approximately 3 percent 

of all chicks marked) hatched from the Central Platte River 

Valley and were subsequently documented on nests as adults. 

All piping plovers returned to nest on different sites from 

the one on which they hatched. A total of 45 instances were 

documented in which an adult plover could either switch to 

nest at a new location or remain at the previous location with 

the onset of a new year. In 39 instances (87 percent), the adult 

nested on the same site as its prior documented nesting attempt 

and in 6 of these instances the adult switched to a new nesting 

location between years. There were 13 of 75 uniquely identifiable piping plovers observed to renest (that is, initiate more 

than one nest in a season) during 2009–14; no renests were 

observed among uniquely identifiable least terns. In all but 

one case, piping plover renests were found at the same site as 

the first nest initiated that season. For birds that renested, the 

mean initiation date of the first nest was May 6 and the mean 

initiation date of the second nest was June 8. On average, 

renests were initiated 7.5 days plus or minus 7.3 (SD [standard 

deviation]) following the date the initial nesting attempt was 

‘fated’ (considered either failed or hatched).
2 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Introduction

The Central Platte River Valley is a resource area of 

continental significance to migratory birds. Habitat and food 

provided in this area are important for migration and successful breeding in many species, including waterfowl, shorebirds, 

and passerines (Sherfy and others, 2012a). The Central Platte 

River Valley also provides breeding habitat for a variety of 

migratory birds, including federally endangered interior least 

terns (Sternula antillarum; least tern) and threatened piping 

plovers (Charadrius melodus; Faanes, 1983). Both of these 

species co-occur on many large mid-continent river systems 

where they nest in loosely organized mixed colonies (Thompson and others, 1997; Haig and Elliott-Smith, 2004). 

At the onset of settlement in the mid-1800s, the Platte 

River exhibited a wide, mostly unvegetated, braided planform 

with an average width on the order of 3,800 ft (Williams, 

1978). Water development began in tandem with settlement 

and the Platte River is now (2015) one of the most heavily 

regulated rivers in the world with more than seven thousand 

diversion rights and seven million acre-ft of reservoir storage (Simons and Associates Inc., 2000). The Platte River 

has narrowed substantially since the mid-1800s through the 

expansion of cottonwood forest into previously active parts 

of the channel (Williams, 1978; Eschner and others, 1983; 

Johnson, 1994; Simons and Associates, 2000; Murphy and 

others, 2004). Most river channel narrowing took place during the 1940s and 1950s with channel area stabilizing by the 

1980s (Johnson, 1994). Woody vegetation expansion in the 

Platte River has been studied extensively with most investigators concluding that alterations in hydrology caused by water 

development were the primary driver of narrowing (Currier, 

1997). Alternative hypotheses of specific mechanisms of narrowing include a reduction in peak flow magnitudes and associated ability to scour vegetation (Williams, 1978; Murphy 

and others, 2004), a reduction in flow during the cottonwood 

germination period leading to increased recruitment (Johnson, 1994; Simons and Associates Inc., 2000), and a decrease 

in desiccation mortality of seedlings in summer as the river 

transitioned from ephemeral to perennial because of irrigation 

return flows (Schumm, 2005). 

The first records of least terns and piping plovers in the 

Central Platte River Valley date to the 1940s, after the bulk of 

water development had already taken place and the channel 

was narrowing (Wycoff, 1960). Accordingly, it is not possible to infer a decline in habitat suitability or corresponding 

declines in species use or productivity with historical timeframes from the data that are available. The first recorded least 

tern observations in the Central Platte River Valley was made 

near Lexington, Nebraska (fig. 1). Nesting was observed on 

a low sandbar in the channel, high in-channel islands created 

by sand mining, and at adjacent sandpits (Wycoff, 1960). No 

information on piping plover use and productivity is currently 

(2015) available before the onset of systematic survey efforts 

in 1979 (Pitts, 1988). Since 1979, approximately 88 percent 

of least tern nests and 75 percent of piping plover nests in the 

Central Platte River Valley have been observed on sandpits 

(Faanes, 1983; Sidle and Kirsch, 1993; Kirsch, 1996; Jenniges and Plettner, 2008; Sherfy and others, 2012a; Platte 

River Recovery Implementation Program, 2014). Approximately 9 percent of least tern nests and 18 percent of piping 

plover nests have been observed on constructed or managed 

in-channel sandbar habitat and 3 percent of least tern nests 

and 7 percent of piping plover nests have been observed on 

naturally formed sandbars (Executive Director’s Office, 2015). 

In 2009, the Platte River Recovery Implementation 

Program (hereafter ‘PRRIP’) began constructing and managing additional off-channel (sandpits) and a few in-channel 

(midchannel sandbars) nesting sites to add to the existing 

habitat that was mechanically created or managed by other 

conservation entities. The goal of this work was to improve 

the foraging and nesting habitat conditions for piping plovers 

and least terns and thus facilitate population growth and continued viability. At the same time, researchers were collecting 

site-specific data on nest success, and chicks and adults of 

both species were the subject of a mark-recapture program 

aimed at estimating survival and movement. This work has 

produced demographic data for both species that span the 

entire lifecycle (that is, from egg laying through survival of 

adults). It also presents a unique opportunity as conditions are 

ideal to investigate what demographic characteristics contribute to a shift in breeding population distribution throughout 

the Central Platte River Valley.

To this end, the demographic data collected during 

2009–14 were compiled and, where possible, used to assess 

how the vital rates (for example, nest survival, chick survival, 

and so on) of both species were related to type and age of nesting habitat. The analysis focused on addressing the following 

five objectives:

I. Reproductive Success—Quantify abundance, distribution, reproductive success and reproductive habitat 

parameters in the study area. 

II. Colonization—Quantify colonization rate of nesting 

habitat by local adults compared to immigrant adults.

III. Adult Survival and Recruitment—Quantify survival 

rates of after-hatch-year nesting adults and hatch year 

adults (that is, survival from banding as a chick to first 

year as an adult).

IV. Dispersal—Quantify dispersal of breeding adults 

between units of nesting habitat. 

V. Renesting—Quantify frequency, timing and location of 

renesting attempts by adults with failed nests or broods 

of chicks.

The purpose and scope of this report is to summarize the 

least tern and piping plover demographic data relative to these 

objectives and to place our results in the context of previous 

research on both species. At present (2015), insufficient sample sizes prevent a definitive assessment of how population 

demography corresponds to habitat type; however, the results 

presented in this report summarize the patterns observed to 

date and shed light on future research avenues. 
Base modified from Platte River Recovery Im

Figure 1. Central Platte River Valley study area during 2009–14.
4 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Study Area

This study includes the population of least terns and 

piping plovers that nest within the Central Platte River Valley 

beginning at the junction of U.S. Highway 283 and Interstate 80 near Lexington, Nebraska, and extending eastward 

to Chapman, Nebraska (fig. 1). The study area includes 

approximately 90 miles of the Platte River and sandpits within 

3.5 miles of the main channel or within 2 miles of a side 

channel if the side channel extends beyond 3.5 miles of the 

main channel. The 2009–10 field efforts for the foraging ecology study were focused on sites where the highest numbers of 

least tern and piping plover nests had previously been reported 

(Sherfy and others, 2012a). Other potential sites were sought 

for inclusion each year, but the foraging ecology study was 

limited to 6 preselected focal areas. When research efforts 

were extended to 2011–14, additional sites were added as 

they became available with acquisition or management action 

(table 1).

Table 1. Central Platte River Valley least tern and piping plover nesting sites included in analyses of 

reproductive success, dispersal, renesting frequency, and colonization.

[‘Site type’ indicates whether the site is located along the Platte River or an off-river sandpit, ‘First year available’ 

indicates the year (when known) that the site first had nesting habitat available. All sites were located in Nebraska.]

Site name Site type First year available

DeWeese–Alda Sandpit <2001

Trust Wildrose–East Sandpit 2008

Wild Rose Ranch Island River 2008

Alda Farms Island River <2001

Binfield Islands River 2014

Leaman East (Sandpit) Sandpit 2013

Leaman West (Islands) River 2013

Uridil Property River 2009

Dippel Tract River 2007

Triplett Trail Tract River 2008

Rowe Headquarters River 2008

Dinan Tract River 2007

Younkin Tract River 2009

Broadfoot–Newark West Sandpit 2011

Wyoming Property River NA

Broadfoot–Kearney South Sandpit 2010

Elm Creek Island Complex East River 2013

Johnson Sandpit Sandpit <2001

Elm Creek Island Complex West River <2001

Blue Hole Sandpit <2001

Cottonwood Ranch PRRIP Island River 2014

Cottonwood Ranch Sandpit Sandpit 2011

Dyer Sandpit Sandpit 2011

Lexington Island River <2001

Lexington Sandpit Sandpit <2001

Paulsen’s Lexington Pit Sandpit 2012
Methods 5

Methods

Field Methods

Surveys of sites with nests or broods took place at least 

twice per week. All sites PRRIP considered suitable bare-sand 

nesting habitat in the surveyed area were included (fig. 1). 

A crew of 3 to 5 technicians systematically searched for nests 

within each area approximately every 2 to 3 days from May 1 

to mid-August, during 2009–14. A systematic search consisted 

of the crew members spaced 5 to 10 meters apart walking 

parallel to each other in a zig-zag pattern as they scanned the 

ground for nests. A nest was defined as a scrape containing 

one or more eggs or eggshell fragments. Nests also occasionally were found incidentally when technicians visited sites 

for other purposes. Nest locations were recorded with Global 

Positioning System (GPS) units and incubation stage was 

estimated by floating one or more eggs on the day of nest 

discovery. Nests were revisited every 2 to 3 days, except near 

the expected hatch date then they were revisited daily to determine nest fate. Nests were considered successful if at least one 

egg hatched. Nest fate was determined from evidence at the 

nest and recorded as follows: successful, probable successful, 

probable failure, failure, or fate unknown.

Adult least terns and piping plovers were trapped on nests 

using hoop nets or walk in traps (Hill and Talent, 1990). Trapping took place early or late in the day or when air temperature 

ranged between 15 degrees Celsius (°C) (60 degrees Fahrenheit [°F]) and 32 °C (90 °F), wind was minimal or not disrupting nests, and there was no precipitation. Trapping took place 

at least 48 hours after the onset of incubation, but before pipping. Trapping attempts were aborted if they exceeded 30 minutes as measured from the departure of the bird from the nest 

through completion of the trap attempt. Before trap deployment, eggs from targeted nests were exchanged with artificial 

eggs to reduce potential risk of injury; real eggs were stored 

in small plastic containers cushioned with synthetic batting. 

Once captured, birds were moved to a nearby area away from 

the colony and other nesting birds. Birds were weighed with a 

spring scale. Each adult piping plover was banded with a size 

1A numbered U.S. Geological Survey (USGS) aluminum band 

on the upper leg, a light blue Darvic (Avinet, Inc., Dryden, 

New York) plastic short flag on the opposite upper leg, and as 

many as 2 Darvic color bands on each of the lower legs (total 

of 4 color bands). The banding approach for least tern adults 

was adjusted partway through the study. During 2009–12, each 

adult tern was banded with a size 1A numbered USGS stainless steel band on the lower leg and as many as three celluloid 

bands (size XCL) on the upper leg (two bands per leg). The 

use of celluloid bands was discontinued in 2013 because of 

band retention issues; instead each adult least tern was banded 

with a size 1A numbered USGS stainless steel band on 1 lower 

leg and a 2-character Darvic alpha-numeric band on the other 

lower leg. Crews conducting surveys of nesting habitats carried spotting scopes and recorded band combinations of any 

birds that were resighted. Adults were associated with nests 

based on behavioral observations during resighting as well as 

capture records of previously banded birds.

Crews attempted to mark every least tern and piping 

plover chick encountered. Because nests were visited more 

frequently near the expected hatch date, chicks were typically located in or near the nest bowl and were thus able to be 

banded at a young age. In most cases, this allowed the accurate assignment of each chick to a nest. When unbanded chicks 

were first found outside a nest bowl, no assumptions were 

made about which nest they had hatched from, and their nest 

origin was recorded as unknown. Each piping plover chick 

was initially banded with a light blue flag and USGS size 

1A aluminum metal band on the opposite upper legs (tibia). 

Additionally, 4 colored bands were placed in various positions on the lower legs (tarsometatarsus), positioned to create 

a unique color combination for each bird. Crews attempted to 

mark each least tern chick as soon after hatching as possible, 

and adjusted the banding approach for least tern chicks part 

way through the study. During 2009–12, one colored celluloid 

band was applied above the joint of each leg (tibia), a colored 

band below the joint of one leg (tarsometatarsus), and a USGS 

aluminum metal band below the joint of the other leg. Chicks 

were recaptured and weighed on subsequent visits. When they 

were approximately 15 days post-hatch, color bands were 

moved from the upper to the lower part of the leg to increase 

potential for resighting. This approach was necessary because 

very young least tern chicks cannot carry 2 bands on the same 

leg segment because of small leg size. It was determined that 

band loss issues with celluloid bands were substantial, so the 

banding approach was adjusted in 2013 by applying a unique 

two-character alpha-numeric Darvic plastic band and a USGS 

size 1A stainless steel metal band below the joint of opposite 

legs on each least tern chick. This banding approach appears to 

be superior because band retention is substantially higher for 

Darvic alpha-numeric bands than for celluloid bands on least 

terns. Nesting habitats were surveyed approximately 2−3 times 

a week to identify color-banded individuals that had reached 

fledging age (greater than or equal to 21 days old for plovers, greater than or equal to 16 days old for terns). Surveys 

consisted of stationing 1 or 2 technicians with spotting scopes 

offshore or around the perimeter of sandpits, conducting systematic searches of sandpits or riverine sites, and recapturing 

tern chicks when necessary to confirm identification. All field 

activities were conducted according to protocol outlined in 

Federal Threatened and Endangered permit no. TE121914–7. 

Data Analysis

Reproductive Success—Nest Survival Rates

Because nest visits were frequent and most nests were 

found in laying stage, apparent nest success was deemed an 

appropriate, unbiased estimator of productivity (Johnson and 

Shaffer, 1990; Shaffer, 2004; Sherfy and others, 2012b). Daily 

nest survival rates were estimated separately for least terns 
6 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

and piping plovers. A nest was considered to have survived 

an interval between nest visits if at least one egg was present 

in the nest at the end of the interval or if it was concluded the 

nest hatched (Grant and others, 2005). There was no evidence 

for directional bias in the survival of nests of unknown fate 

and thus unknown-fate nests were excluded from all analyses. 

All models were built using package ‘RMark’ (Laake, 2013) 

in program R and all survival parameters were estimated using 

program MARK (White and Burnham, 1999).

Models were parameterized such that survival was 

dependent on the following covariates: age of the nest at initial 

discovery (NestAge), initiation date (InitiationDate), and 

year (Year). Because most of the existing sites in the analysis 

were not monitored (but probably existed and were used as 

nesting sites) before 2001, there was no attempt to associate 

an exact ‘age’ to these sites. Instead, in analyses where sites 

were divided into either ‘first year available’ or ‘after first 

year available’, all ‘existing’ sites were included in the ‘after 

first year available’ class (that is, covariate ‘SiteAgeClass’). 

Whether nest survival rates for both species differed relative to the age class (SiteAgeClass) of the site on which they 

were initiated was examined. For example, in the year nesting 

habitat was first available at a site this site was considered part 

of the ‘first year available’ age class. Sites that had existed for 

more than one year were considered part of the ‘after first year 

available’ age class. Finally, we examined whether nests initiated on sites that had been created (Created), through either 

physical construction of a new site or new vegetation management regimes, during the 2009–14 interval differed from those 

that were preexisting. These ‘created’ sites included Leaman 

East (Sandpit), Broadfoot – Newark West, Cottonwood Ranch 

PRRIP Island, Cottonwood Ranch Sandpit, and Dyer Sandpit 

(see table 1). Because of a low number of samples, there was 

no examination of the differences in nest survival based on 

whether nests were initiated at sandpit or river locations.

Covariates were added in a stepwise fashion; the first 

model set included each covariate individually, which was 

then compared to a ‘null’ (intercept only) model. Models were 

ranked using Akaike’s Information Criterion adjusted for small 

sample size (AICc); the model with the lowest AICc value was 

considered the most parsimonious. Covariates whose inclusion 

had resulted in a model that had outcompeted the null model 

or top model from the previous step were added to the top 

model from the previous step. Finally, additive associations 

between covariates were explored. The top models from each 

step in the model selection tables were reported.

An abbreviated analysis of created sites of known-age 

only was used to examine whether age class effects were due 

to whether a site was a created site or an ‘existing’ site (that is, 

a site with nesting habitat available before 2009) and whether 

there were any linear effects of actual site age (SiteAge). Sites 

of known age were collapsed into two classes: first year available for nesting and after first year available (for site-specific 

‘first year available’ see table 1). By using sites of only known 

ages ‘site age’ (that is, the number of years that had passed 

since initial availability of a site) was able to be included as 

a continuous covariate in the analysis. The process of model 

selection described in the previous paragraph was followed.

Reproductive Success—Chick Survival to 

Fledging Age

Daily resightings and recaptures of uniquely marked 

piping plover and least tern chicks and Cormack-Jolly-Seber 

(CJS) models in program MARK (White and Burnham, 1999) 

were used to analyze age-structured capture histories and 

estimate the daily apparent survival (φ) and detection probability (p) of both species. Although piping plover chicks were 

considered fledged if alive at 21 days and least tern chicks 

were considered fledged at 16 days of age, capture histories 

were allowed to extend slightly past this point because sites 

were not always visited on the exact day of fledging. There 

were 25 occasion capture histories created for piping plovers banded at younger than 21 days of age and 18 occasion 

capture histories created for least terns banded at younger than 

16 days of age. For each occasion (that is, day of age), a chick 

received a 1 if its site was visited and the chick was resighted 

or recaptured, a 0 if the site was visited but the chick was not 

seen, and was censored (.) if the site was not visited. Due to 

data limitations differences in chick survival based on whether 

chicks hatched at sandpit or river locations were not examined.

Models of all combinations of our parameterizations for 

detection and apparent survival probability were built using 

package RMark in program R and estimated parameters for 

apparent survival and detection using program MARK. The 

degree of overdispersion (ĉ) was estimated using program 

RELEASE and then used to calculate quasi-AICc (QAICc), 

which was then used to rank models. The model with the lowest QAICc value was considered the most parsimonious. 

For both species, models were parameterized such 

that detection probability was dependent on chick age as a 

log-linear trend (Age) and the year a chick was hatched and 

resighted (Year). The effect of targeted searching (Target), 

which designated days on which crews were only visiting sites 

to resight/recapture chicks, was controlled for. To account for 

the fact that detection probability was likely different on days 

in which targeted chick searches took place, the covariate ‘Target’ was added to our parameterization of chick detection (see 

Roche and others, 2014). 

When parameterizing models for apparent survival, 

covariate effects were examined by modeling chick-age as a 

log-linear trend (Age) and adding the year a chick was hatched 

and resighted (Year). In addition, whether survival rates for 

both species differed relative to the age class (SiteAgeClass) 

of the site on which they were hatched was examined. For 

example, in the year nesting habitat was first available at a 

site, this site was considered part of the ‘first year available’

age class. Sites that had existed for more than 1 year were 

considered part of the ‘after first year available’ age class. 

All parameterizations for detection probability were fit 

first. In all cases, the parameterization of apparent survival 
Methods 7

was constrained to a model in which survival was described 

as an additive effect of ‘Age’ and Year’. Parameterizations of 

detection probability were built that were described by (1) a 

null model, (2) Age, (3) Target, (4) Age + Target, (5) Target 

+ Year, and (6) Age + Target + Year. The top model (lowest 

QAICc) was selected for our parameterization of detection 

probability when parameterizing and selecting among models 

for apparent survival. 

When parameterizing models for apparent survival, 

covariates were added in a stepwise fashion; the first model 

set included each covariate individually, which was then 

compared to a null (intercept only) model. Models were 

ranked using QAICc; the model with the lowest QAICc value 

was considered the most parsimonious. All covariates whose 

inclusion had resulted in a model that had outcompeted the 

null model or top model from the previous step were included 

in the top model from the previous step. Finally, only additive associations between covariates and nest survival were 

explored. The top models from each step in the model selection tables were reported.

Colonization

There was a subset of 11 sites included in the colonization analysis (table 1). Of these 11 sites, 8 were sites that were 

considered created through either physical construction or 

habitat modification (for example, vegetation removal) and 

well-monitored by USGS crews during 2009–14 (hereafter 

referred to as ‘created’ sites). These created sites included 

the following: Binfield Islands, Broadfoot-Kearney South, 

Broadfoot-Newark West, Cottonwood Ranch PRRIP Island, 

Cottonwood Ranch Sandpit, Dyer Sandpit, Leaman East 

(Sandpit), and Leaman West (Islands). Three of these sites 

were located on the Platte River, whereas the other five were 

sandpit sites. For comparative purposes, three sandpit sites 

were included that existed before 2009 and were consistently 

monitored by USGS crews during 2009–14 (hereafter ‘existing’ sites). These existing sites included the following: Blue 

Hole, Johnson Sandpit, and Lexington Sandpit. At all sites and 

for both species, USGS crews monitored nests, banded chicks 

and adults, and resighted throughout the course of the season 

(2009–14).

For sites that were created during 2009–14 (and thus 

were of known age) site age (covariate ‘SiteAge’) was calculated as the current year, less the first year in which nesting 

habitat was available at a site, plus 1 year. For example, if 

habitat modification took place half-way through 2011, the site 

was not considered ‘available’ for nesting until 2012 (when 

the site had an age of 1 year); in 2013 this site would be considered 2 years old (for example, 2013 – 2012 + 1 = 2). The 

year nesting habitat was considered to have first been available 

at a site is presented in table 1. Because most of the existing 

sites in the analysis were not monitored (but probably existed 

and used as nesting sites) before 2001, there was no attempt 

to associate an exact ‘age’ to these sites. Instead, in analyses 

where sites were divided into either ‘first year available’ or 

‘after first year available’, all ‘existing’ sites were included in 

the ‘after first year available’ class (covariate ‘SiteAgeClass’). 

When uniquely marked piping plovers and least terns were of 

known age (that is, banded as chicks) and nesting at one of the 

aforementioned 11 sites during 2010–14, they were assigned 

to one of two age classes: first year nesting adult (FY) or after 

first year nesting adult (AFY). As banding began in 2009, 

before 2010, there were no uniquely marked FY birds. 

Information on band resighting collected during nest 

monitoring was used to summarize the number of unbanded 

piping plovers or least terns relative to the number of marked 

piping plovers or least terns for each site in each year 

(2009–14). Finally, as with previous summaries, the number 

of nests present at each site in each year was tabulated for both 

species. The summaries were restricted to piping plovers and 

least terns of known age (that is, banded as chicks). 

General linear regression models were built to assess 

the effect of site age on the number of nests present at a site. 

In each analysis, the effect of the following covariates was 

investigated: ‘SiteAge’ (in years), ‘SiteAgeClass’ (that is, 

either ‘first year available’ or ‘after first year available’), species (Species), as well as species by site age and site age class 

combinations. Models were compared relative to a null model 

with no covariates. Models were ranked using AICc and the 

results from the top-ranked model (that is, lowest AICc) were 

interpreted. Only sites and individual birds of known age were 

included in these analyses.

Apparent Survival of Juveniles and Nesting 

Adults

Annual resighting and recapture data collected on 

uniquely marked adult piping plovers and least terns observed 

in the Central Platte River Valley during 2009–14 and CJS 

models built-in program MARK were used to estimate the 

annual apparent survival and detection probability for both 

species. So that estimates of juvenile survival for piping 

plovers would be comparable with other published estimates, 

individuals banded as chicks were only included in the analysis if they were recaptured or resighted between 20–35 days of 

age (approximate fledging age, see Catlin and others, 2014). 

For least terns, individuals banded as chicks were included if 

they were recaptured or resighted between 16–30 days of age 

(approximate fledging age, Roche and others, 2014). Although 

this reduced the sample size, by following this process, 

prefledging mortality was excluded from the estimates of 

juvenile survival. 

Cormack-Jolly-Seber models produce estimates of 

‘apparent survival’, in which true survival is confounded with 

site fidelity, and ‘detection probability’, in which true detection (whether or not a bird that is present is seen) is confounded with temporary emigration from a resighting location. 

Because of consistent field effort and field methodologies 

during the 2009–14, it was assumed the annual probability of 

detecting a uniquely marked least tern or piping plover was 
8 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

constant. For piping plovers intercept-only parameterizations 

for p were built; however, least terns are not believed to return 

to the breeding grounds until their second year as an adult 

(Massey and others, 1992). As a result, least tern detection was 

modeled with two age-classes and no year effects. Detection 

probability was fixed to 0 for least terns in their first year as 

an adult. 

Models for apparent survival were parameterized based 

on age class only (AgeClass; that is, juvenile survival compared to adult survival). Year-specific apparent survival or 

detection probabilities were not estimated because of small 

sample sizes. CJS models were built using package RMark in 

program R and generated parameter estimates using program 

MARK. The degree of overdispersion (ĉ) was estimated 

using the median-ĉ test and this was used to calculate quasiAICc (QAICc), which was then used to rank models. The 

model with the lowest QAICc value was considered the most 

parsimonious.

Dispersal and Philopatry

Recapture and resighting data were used to quantify 

the number of times uniquely identifiable individuals moved 

between nesting sites to describe how uniquely marked piping plovers and least terns were using habitat in the Central 

Platte River Valley. These data were summarized based on the 

number of uniquely marked individuals that moved between 

habitat types (river or sandpit) and by individual site as after 

first year adults (that is, movements between the first nesting 

attempt through multiple years) or as first year adults (that is, 

movement between hatch site habitat type and first nesting 

attempt habitat type). 

Two forms of dispersal were computed for both species: natal dispersal—the distance between the first observed 

nest of an adult bird and the nest at which it hatched at, and 

nesting adult dispersal—the distance between the first nest of 

an adult in yeart-1 and the first nest of that same adult in yeart.

When adults were not observed nesting in consecutive years, 

the nesting adult dispersal was calculated as the distance 

between the location of the first nest at the last recorded nesting event and the location of the first nest at the subsequent 

nesting event. For example, if an adult nested in 2012, was not 

observed nesting in 2013, but then was again observed nesting 

in 2014, adult dispersal distance was calculated as the distance 

between the first nest in 2012 and the first nest in 2014. We 

chose to include non-consecutive nesting years in our analyses 

because our sample sizes were small and thus we wished to 

include all available data so as to completely describe movement between nesting locations. Although, by this example, 

we would not know where the individual nested in 2013, by 

including all information, we would know if the individual 

used a different site in 2012 than in 2014 and how far away 

these locations were from each other. However, the ‘dispersal 

distance’, cannot be interpreted as if a plover or tern made a 

straight-line flight between the locations. The R package “sp” 

(Pebesma and Bivand, 2005; Bivand and others, 2013) was 

used to compute the straight-line distance between the Universal Transverse Mercator (UTM) nest locations of nests. 

Renesting

Because within-year inter-nest dispersal, otherwise 

known as renesting, was of special interest, each of these 

events was examined separately from the summary of interannual dispersal. Package “sp” in program R was used to 

compute the straight-line distance between the UTM locations of nests initiated in the same year by the same uniquely 

marked individual. Each association of an adult with a nest 

within a year was considered a unique inter-nest dispersal 

movement. Each unique inter-nest dispersal movement was 

classified according to (1) whether the adult moved to a new 

site or stayed on the same site, (2) the adult moved to a different habitat type (that is, river or sandpit), (3) the adult moved 

to a ‘created’ or ‘existing’ site, (4) the fate of the first nest, and 

(5) the fate of renest.

For uniquely marked least terns and piping plovers that 

renested, the mean initiation dates of first nests and renests 

were calculated for all years (2009–14). Additionally, the 

average interval between the estimated termination date of the 

first nest and the initiation date of the second (or subsequent) 

nest was calculated and this value was used to calculate mean 

renesting intervals for the study period. For each year, the 

number of first nests initiated by at least one uniquely marked 

adult and the number of known ‘renests’ initiated by at least 

one uniquely marked adult were reported. The total number 

of uniquely identifiable least terns and piping plovers known 

to have nested and known to have renested was also reported. 

No information on nests associated with non-uniquely marked 

adults were included as these could not be accurately classify 

as ‘first nests’ or ‘renests’. 

Migratory, Winter, and other non-Central Platte 

River Valley Resightings of Piping Plovers

All resightings of piping plovers banded in the Central 

Platte River Valley and observed elsewhere were compiled 

and summarized by state and year of the observation. A unique 

event was defined as a banded bird within a season (that is, we 

counted 2 unique events if the same bird was seen in 2 different years on the wintering grounds, and 1 unique event if the 

same bird was seen multiple times in the same season). Only 

individuals with complete color band combinations that could 

be associated with a USGS metal band number as a unique 

identity were included. 
Results 9

Results

Reproductive Success—Nest Survival Rates

Least Terns.—A total of 366 least tern nests monitored 

at river (n = 4 nests) and sandpit (n = 362 nests) focal sites 

during 2009–14 were included in the nest survival analysis 

(table 2). Of the 362 least tern nests, 29 (8 percent of those 

monitored) were initiated in the first year a site was available for nesting. During 2009–14, mean daily nest survival 

was 0.9742 (95-percent CI: 0.9692–0.9783) and, using 

daily survival estimates from the intercept-only (constant 

survival) model, cumulative survival of least tern nests was 

0.59 (95-percent CI: 0.53–0.65) from the date the first egg 

was laid through the end of incubation (21 days). Models 

that incorporated annual variation in daily nest survival rates 

were supported for least terns (table 3) suggesting that nest 

survival rates were annually variable (see fig. 2). Additionally, 

as the age of the tern nest at its discovery increased, survival 

decreased (β

ˆ nestage = -0.07, 95-percent CI: -0.11 to -0.02) and 

daily nest survival rates were higher at older sites (those in 

the ‘after first year available’ site age class; see fig. 3). For the 

181 least tern nests included in the abbreviated analysis of nest 

survival relative to site age and site age class at sites created 

since 2009, year continued to explain more of the variability in 

nest survival than the age class of the site a least tern nest was 

initiated on (table 4).

Piping Plovers.—A total of 148 piping plover nests 

monitored at river (n = 10 nests) and sandpit (n = 138 nests) 

focal sites during 2009–14 were included in the nest survival 

analysis (table 5). Of these, 7 piping plover nests (5 percent 

of those monitored) were initiated in the first year a site was 

available for nesting. During 2009–14, mean daily nest survival was 0.9880 (95-percent CI: 0.9836–0.9912) and, using 

daily survival estimates from the intercept-only (constant survival) model, cumulative nest survival was 0.66 (95-percent 

CI: 0.57–0.74) from the date the first egg was laid through the 

end of incubation (35 days) (fig. 4). Models that incorporated 

annual variation in daily nest survival rates received little support for piping plovers (table 6). For the 59 piping plover nests 

included in the abbreviated analysis of nest survival relative 

to site age and site age class only at sites created since 2009, 

there was no evidence that site age or age class played a role 

in explaining variability in nest survival for piping plovers 

(table 7).

Reproductive Success—Chick Survival to 

Fledging Age

Least Terns.—Chick survival was estimated for 523 least 

tern chicks hatched from river (n = 2 chicks) or sandpit (n = 

521 chicks) focal sites during 2009–14 (for total marked 

during 2009–14 see table 8). Of the 523 least tern chicks, 

32 (6 percent of those marked) were hatched on a site in the 

first year it was available. The best-supported model for least 

tern chick survival included chick age, year, and age class of 

the hatch site all as additive (that is, non-interacting) effects 

(table 9). Mean daily chick survival was 0.9602 (95-percent 

CI: 0.9515–0.9673) and cumulative chick survival to fledging 

(16 days) using daily survival estimates from the interceptonly model was 0.54 (95 -percent CI = 0.48–0.61; see fig. 5). 

The probability of a chick surviving to fledging, however, was 

approximately 1.5 times higher at older sites (that is, those in 

the ‘after first year available’ site age class) than in the first 

year of nesting habitat availability (see fig. 6).

Piping Plovers.—Chick survival was estimated for 

408 piping plover chicks hatched from river (n = 17 chicks) or 

sandpit (n = 391) focal sites during 2009–14 (for total marked 

during 2009–14 see table 8). Of the 408 piping plover chicks, 

only 18 (5 percent of those marked) were hatched on a site 

in the first year it was available. The best-supported model 

for piping plover chick survival was an intercept-only model 

(table 10) suggesting chick survival to fledging (21 days) 

did not differ significantly by year, chick age, or site age 

class. Mean daily chick survival was 0.9621 (95-percent CI: 

0.9514–0.9706) and cumulative chick survival to fledging 

using daily survival estimates from the intercept-only model 

was 0.46 (95-percent CI = 0.37–0.56; see fig. 7). 

Colonization

Least Terns.—A total of 33 nests were documented at 

created sites during the first year of the site’s availability: there 

were 3 nests found at Broadfoot—Kearney South in 2010, 

19 nests found at Broadfoot—Newark West in 2011, 5 nests 

found at Dyer Sandpit in 2011, and 6 nests found at Leaman 

East (sandpit) in 2013. The number of least tern nests present 

at a created site was associated with the age class of that site 

(see table 11), with more tern nests associated with older sites 

(that is, those in the ‘after first year available’ site age class). 

There were no uniquely marked least terns that either 

nested or were observed at a created site in the first year it 

was available. There were 3 least terns that were observed on 

created sites as AFY individuals; 2 least terns had originally 

hatched at Blue Hole, and 1 least tern had originally hatched at 

Broadfoot—Kearney South. No banded least terns were seen 

on a site in the first year it was available (see table 12).
10 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 2. Number of successful and failed least tern nests on the Central Platte River Valley during 

2009–14 included in the nest survival analysis.

[Unknown-fate nests were excluded from nest survival analysis.]

2009 2010 2011 2012 2013 2014 Total

Success 22 27 33 46 31 64 223

Fail 9 17 23 13 26 55 143

Total 31 44 56 59 57 119 366

Table 3. Nest survival models used to estimate daily nest survival rates for least tern nests initiated in the Central Platte River Valley 

during 2009–14.

[Models were ranked using Akaike’s Information Criterion adjusted for small sample size (AICc); here we present the change in AICc relative to the top model 

(ΔAICc), the number of model parameters (k), and the model deviance (Deviance). (‘S’: daily nest survival, ‘+’: designates an additive relationship, ‘Intercept’: 

intercept model, ‘Created’: a site was either ‘created’ or ‘pre-existing’ [categorical], ‘NestAge’: the age in days of the nest when first found [continuous], ‘InitiationDate’: the ordinal date the nest was initiated [continuous], ‘Year’: the year [categorical] the nest was initiated, ‘SiteAgeClass’: as site was either in the ‘first 

year of availability’ or in a year ‘after the first year of availability’ [categorical]).]

Model (S) k ∆AICc Deviance

Year + NestAge + SiteAgeClass* 8 0.00 834.61

Year + NestAge 7 2.03 838.64

Year 6 6.17 844.79

Intercept 1 17.15 865.78

*AIC for the top-ranked model was 850.6.

Figure 2. Cumulative nest survival (21 days) rates of least tern nests in the Central Platte River Valley, 2009–14. (Circles with vertical 

bars represent annual cumulative survival estimates with 95-percent confidence intervals generated from model S[Year + NestAge; 

table 3]. The thick horizontal gray line with two additional thin gray lines represents the mean cumulative survival estimate and 

95-percent confidence intervals respectively during 2009–14 generated from model S[Intercept; table 3]).
Results 11

Figure 3. Cumulative nest survival rates (21 days) based on nest site age class for least tern nests initiated in the Central Platte 

River Valley, 2009–14. (Open circles indicate the first year of site availability. Closed circles indicate a year after the first year of site 

availability. Circles with vertical bars represent annual cumulative survival estimates with 95-percent confidence intervals generated 

from S[Year + NestAge + SiteAgeClass; table 3]. The thick horizontal gray line with two additional thin gray lines represents the mean 

cumulative survival estimate and 95-percent confidence intervals respectively during 2009–14 generated from model S[Intercept; 

table 3].)

Table 4. Nest survival models used to estimate daily nest survival rates for least tern nests initiated 

on created sites in the Central Platte River Valley during 2009–14.

[Models were ranked using Akaike’s Information Criterion adjusted for small sample size (AICc); here we present the 

change in AICc relative to the top model (ΔAICc), the number of model parameters (k), and the model deviance (Deviance). (‘S’: daily nest survival, ‘+’: designates an additive relationship, ‘Intercept’: intercept model, ‘Created’: a site 

was either ‘created’ or ‘pre-existing’ [categorical], ‘NestAge’: the age in days of the nest when first found [continuous], 

‘InitiationDate’: the ordinal date the nest was initiated [continuous], ‘Year’: the year [categorical] the nest was initiated, 

‘SiteAgeClass’: as site was either in the ‘first year of availability’ or in a year ‘after the first year of availability’ ‘+’: 

designates an additive relationship [categorical], ‘SiteAge’: the number of years a site has been available to be nested at 

[continuous]).]

Model (S) k ∆AICc Deviance

Year* 5 0.00 373.02

SiteAgeClass + Year 6 0.39 371.40

SiteAgeClass 2 1.94 380.98

Intercept 1 10.22 391.26

SiteAge 1 75.07 456.11

*AIC for the top-ranked model was 383.0.
12 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 5. Number of successful and failed piping plover nests in the Central Platte River Valley 

during 2009–14 included in the nest survival analysis.

[Unknown-fate nests were excluded from nest survival analysis.]

2009 2010 2011 2012 2013 2014 Total

Success 3 12 20 23 18 32 108

Fail 5 9 6 8 5 7 40

Total 8 21 26 31 23 39 148

Figure 4. Cumulative nest survival rates of piping plover nests (35 days) in the Central Platte River Valley, 2009–14. (Circles with 

vertical bars represent annual cumulative survival estimates with 95-percent confidence intervals generated from S[Year; table 6]. 

The thick horizontal gray line with two additional thin gray lines represents the mean cumulative survival estimate and 95-percent 

confidence intervals respectively for 2009–14 generated from model S[Intercept; table 6].)
Results 13

Table 6. Nest survival models used to estimate daily nest survival rates for piping plover nests 

initiated in the Central Platte River Valley during 2009–14.

[Models were ranked using Akaike’s Information Criterion adjusted for small sample size (AICc); here we present 

the change in AICc relative to the top model (ΔAICc), the number of model parameters (k), and the model deviance 

(Deviance). (‘S’: daily nest survival, ‘+’: designates an additive relationship, ‘Intercept’: intercept model, ‘Created’: a 

site was either ‘created’ or ‘pre-existing’ [categorical], ‘NestAge’: the age in days of the nest when first found [continuous], ‘InitiationDate’: the ordinal date the nest was initiated [continuous], ‘Year’: the year [categorical] the nest was 

initiated, ‘SiteAgeClass’: a site was either in the ‘first year of availability’ or in a year ‘after the first year of availability’ 

[categorical]).]

Model (S) k ∆AICc Deviance

Intercept* 1 0.00 344.63

NestAge 2 0.07 342.70

InitiationDate 2 0.94 343.57

Created 2 1.05 343.69

SiteAgeClass 2 1.40 344.03

Year 6 1.76 336.37

*AIC for the top-ranked model was 346.64.

Table 7. Nest survival models used to estimate daily nest survival rates or piping plover nests 

initiated on sites created in the Central Platte River Valley during 2009–14.

[Models were ranked using Akaike’s Information Criterion adjusted for small sample size (AICc); here we present 

the change in AICc relative to the top model (ΔAICc), the number of model parameters (k), and the model deviance 

(Deviance). (‘S’: daily nest survival, ‘+’: designates an additive relationship, ‘Intercept’: intercept model, ‘Created’: a 

site was either ‘created’ or ‘pre-existing’ [categorical], ‘NestAge’: the age in days of the nest when first found [continuous], ‘InitiationDate’: the ordinal date the nest was initiated [continuous], ‘Year’: the year [categorical] the nest was 

initiated, ‘SiteAgeClass’: a site was either in the ‘first year of availability’ or in a year ‘after the first year of availability’ 

[categorical], ‘SiteAge’: the number of years a site has been available to be nested at [continuous]).]

Model (S) k ∆AICc Deviance

Intercept* 1 0.00 128.12

NestAge 2 1.51 127.63

SiteAgeClass 2 1.70 127.81

InitiationDate 2 1.99 128.10

Year 4 3.98 126.07

SiteAge 2 66.26 194.38

*AIC for the top-ranked model was 130.12.

Table 8. Number of least terns and piping plovers banded by age and year in the Central Platte River Valley (2009–14).

Species Age 2009 2010 2011 2012 2013 2014 Total

Least tern Adult 16 7 4 9 33 28 97

Least tern Chick 35 74 98 103 99 114 523

Piping plover Adult 9 12 2 12 12 11 58

Piping plover Chick 25 64 68 86 64 106 413
14 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 9. Cormack-Jolly-Seber survival models used to estimate daily survival rates for least tern 

chicks hatched in the Central Platte River Valley during 2009–14.

[Models were ranked using Quasi-Akaike’s Information Criterion adjusted for overdispersion (ĉ = 0.71) and small 

sample size (QAICc); here we present the change in QAICc relative to the top model (ΔQAICc), the number of model 

parameters (k), and the model deviance (QDeviance). (‘φ’: daily survival rates, ‘+’: designates an additive relationship, 

‘Intercept’: intercept model, ‘Age’: a log-linear trend of chick age in days [continuous], ‘Year’: the year [categorical] 

the nest was initiated, ‘SiteAgeClass’: a site was either in the ‘first year of availability’ or in a year ‘after the first year 

of availability’ [categorical], ‘Target’: age-specific covariate indicating that the site a chick was hatched on was the 

subject of a ‘targeted’ search [time-varying, categorical]). For all models detection probability (p) was parameterized as 

p(Target + Age + year).]

Model (φ) k ∆QAICc QDeviance

Age + Year + SiteAgeClass* 15 0.00 4,230.61

Age + Year 14 0.78 4,233.45

Intercept 9 40.21 4,283.07

*QAIC for the top-ranked model was 4,261.01.

Figure 5. Cumulative survival rates of least tern chicks to fledging age (16 days) in the Central Platte River Valley, 2009–14. (Circles 

with vertical bars represent annual cumulative survival estimates with 95-percent confidence intervals generated from model 

φ[Age + Year; table 9.]. The thick horizontal gray line with two additional thin gray lines represents the mean cumulative survival 

estimate and 95-percent confidence intervals respectively during 2009–14 generated from model φ[Intercept; table 9].)
Results 15

Figure 6. Cumulative survival rates of least tern chicks to fledging age (16 days) based on site age class at which chicks were 

hatched in the Central Platte River Valley, 2009–14. (Open circles indicate the first year of site availability. Closed circles indicate a 

year after the first year of site availability. Circles with vertical bars represent annual cumulative survival estimates with 95-percent 

confidence intervals generated from model φ[Age + Year + SiteAgeClass; table 9]. The thick horizontal gray line with two additional 

thin gray lines represents the mean cumulative survival estimate and 95-percent confidence intervals respectively during 2009–14 

generated from model φ[Intercept; table 9].)

Table 10. Cormack-Jolly-Seber survival models used to estimate daily apparent survival rates for 

piping plover chicks hatched in the Central Platte River Valley during 2009–14.

[Models were ranked using Quasi-Akaike’s Information Criterion adjusted for overdispersion (ĉ = 2.19) and small 

sample size (QAICc); here we present the change in QAICc relative to the top model (ΔQAICc), the number of model 

parameters (k), and the model deviance (QDeviance). (‘φ’: daily apparent survival, ‘+’: designates an additive relationship, ‘Intercept’: intercept model, ‘Year’: the year [categorical] the nest was initiated, ‘Age’: a log-linear trend of chick 

age in days [continuous], ‘Target’: age-specific covariate indicating that the site a chick was hatched on was the subject 

of a ‘targeted’ search [time-varying, categorical]). For all models detection probability (p) was parameterized p(Target 

+ Age + year).]

Model (φ) k ∆QAICc QDeviance

Intercept* 9 0.00 1,496.82

Age 10 0.93 1,495.72

Year 13 6.71 1,495.40

*QAIC for the top-ranked model was 1,514.94.
16 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Figure 7. Cumulative survival rates of piping plover chicks to fledging age (21 days) in the Central Platte River Valley, 2009–14. 

(Circles with vertical bars represent annual cumulative survival estimates with 95-percent confidence intervals generated from 

model φ[Year; table 10]. The thick horizontal gray line with two additional thin gray lines represents the mean cumulative survival 

estimate and 95-percent confidence intervals respectively for 2009–14 generated from model φ[Intercept; table 10].]

Table 11. Summary of least tern nests found at sites created in 

the Central Platte River Valley during 2009–14 by site age in years 

(first year through fifth year) and site age class (first year available 

and after first year available) used in linear and logistic regression 

analyses.

[‘Site Age’: the number of years a site has been available for nesting, ‘Site 

Age Class’: a site was either in the ‘first year of availability’ or in a year ‘after 

the first year of availability’, ‘n’: total number of nests.]

Category n

Site age – 

First year 33

Second year 68

Third year 48

Fourth year 42

Fifth year 11

Site age class – 

First year available 33

After first year available 169
Results 17

Table 12. Summary of uniquely marked least terns resighted 

or recaptured on sites created in the Central Platte River Valley 

during 2009–14 by site age in years, site age class, and tern age 

class used in linear and logistic regression analyses.

[‘FY’: first year nesting adult, ‘AFY’: after first year, ‘Site Age’: the number 

of years a site has been available for nesting, ‘Site Age Class’: a site was 

either in the ‘first year of availability’ or in a year ‘after the first year of availability’, Age Class: age class of resighted/recaptured terns, ‘n’: total number 

of uniquely identifiable least terns.]

Category Age class n

Site age – 

First year FY 0

AFY 0

Second year FY 0

AFY 1

Third year FY 0

AFY 0

Fourth year FY 0

AFY 1

Fifth year FY 0

AFY 1

Site age class – 

First year available FY 0

AFY 0

After first year available FY 0

AFY 3

Piping Plovers.—Although, in general, created sites did 

not have nests in their first year, a total of 7 nests initiated 

in the first year of a site were documented: 2 nests at Broadfoot—Kearney South in 2010, 2 nests at Cottonwood Ranch 

PRRIP Island in 2014, 2 nests at Dyer Sandpit in 2011, and 

1 nest at Leaman East (sandpit) in 2013. The number of piping 

plover nests present at a created site also was associated with 

the age class of that site (see table 13), with more piping plover nests associated with older sites (that is, those in the ‘after 

first year available’ site age class). However, in general, there 

were fewer piping plover nests found at created sites than 

least tern nests. The presence of least tern and piping plover 

nests at created sites was similarly associated with the site age 

class (β

ˆ SiteAgeClass(afterfirstyear) = 2.12) with nests of both species 

approximately 1.7 times more likely to be present at older sites 

relative to sites in their first year of availability (β

ˆ Intercept = 0.0; 

as calculated by log odds).

There were two uniquely marked piping plovers that 

nested at a created site in the first year it was available: one 

at Cottonwood Ranch PRIPP Island in 2014 and the other at 

Dyer Sandpit in 2011. In both cases, the piping plovers were 

first-year nesting adults and had hatched at Blue Hole. There 

were 23 uniquely marked piping plovers of known age recaptured or resighted on created sites as first-year individuals. 

Table 13. Summary of piping plover nests found at sites created 

in the Central Platte River Valley during 2009–14 by site age in 

years and site age class used in linear and logistic regression 

analyses. 

[‘Site Age’: the number of years a site has been available for nesting, ‘Site 

Age Class’: a site was either in the ‘first year of availability’ or in a year ‘after 

the first year of availability’, ‘n’: total number of nests.]

Category n

Site age – 

First year 7

Second year 21

Third year 13

Fourth year 17

Fifth year 9

Site age class – 

First year available 7

After first year available 60

Of these, 12 hatched at Blue Hole, 3 hatched at Lexington 

Sandpit, 5 hatched at Trust Wildrose—East, 1 hatched at 

Leaman East, 1 hatched at Broadfoot—Newark West, and 1 

hatched at Elm Creek Island Complex West. In addition, 9 of 

the 23 FY piping plovers were observed on a created site during the first year the site was available. There were 17 piping 

plovers observed on created sites as individuals in a year after 

their first year (AFY) (7 of these were seen in previous years 

on created sites as FY individuals). Of the 9 piping plovers 

that were observed on created sites for the first time as AFY 

individuals, 1 hatched at Trust Wildrose— East, 1 at Broadfoot—Kearney South, 1 hatched at Blue Hole, 1 hatched at 

Dippel Tract, 1 hatched at Dyer Sandpit, 2 hatched at Johnson 

Sandpit, and 2 hatched at Lexington Sandpit. There were no 

AFY piping plovers observed on sites in the first year of their 

availability (table 14). Additionally, sites that had been available for nesting longer, had a higher number of AFY piping 

plovers observed at them relative to FY plovers (table 14). 

Apparent Survival of Juveniles and Nesting 

Adults

Least Terns.—Juvenile (that is, age of first banding as 

a chick to first year as an adult) and adult annual apparent 

survival was estimated for 262 uniquely identifiable least 

terns that were first marked as either a chick or an adult. The 

annual apparent survival estimate for adult least terns was 0.42 

(95-percent CI = 0.22–0.64) and was 0.14 (95-percent CI = 

0.04– 0.41) for juvenile least terns. The annual detection probability for least terns was 0.42 (95-percent CI = 0.17– 0.71).

Piping Plovers.—Juvenile (that is, age of first banding 

as a chick to first year as an adult) and adult annual apparent 

survival was estimated for 247 uniquely identifiable piping 
18 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 14. Summary of uniquely marked piping plovers resighted 

or recaptured at sites created in the Central Platte River Valley 

during 2009–14 by site age in years, site age class, and plover age 

class used in linear and logistic regression analyses. 

[‘FY’: first year nesting adult, ‘AFY’: after first year, ‘Site Age’: the number 

of years a site has been available for nesting, ‘Site Age Class’: a site was 

either in the ‘first year of availability’ or in a year ‘after the first year of availability’, ‘Age Class’: age class of resighted/recaptured terns, ‘n’: total number 

of uniquely identifiable piping plovers).]

Category Age class n

Site age – 

First year FY 9

AFY 0

Second year FY 7

AFY 5

Third year FY 2

AFY 13

Fourth year FY 5

AFY 9

Fifth year FY 2

AFY 4

Site age class – 

First year available FY 9

AFY 0

After first year available FY 15

AFY 17

plovers that were first marked as either a chick or an adult. The 

annual apparent survival estimate for adult piping plovers was 

0.76 (95-percent CI = 0.65–0.85) and was 0.20 (95-percent 

CI = 0.14– 0.29) for juvenile piping plovers. The annual 

detection probability piping plovers was 0.69 (95-percent CI = 

0.56–0.79). 

Dispersal and Philopatry

Least Terns.—Four least tern chicks hatched from the 

Central Platte River Valley and were subsequently captured 

on nests as adults, providing insight into age at first breeding 

and hatch-year dispersal tendencies (table 15). Of these, three 

nested as adults in the second year after hatch, and one was 

not caught until 4 years after hatch. Two least terns returned to 

nest on the same site at which they had hatched (one at Broadfoot-Kearney South and one at Blue Hole) for a mean distance 

of 0.153 km ± 0.069 kilometers (km) standard deviation (SD). 

The remaining 2 birds moved to new nesting areas; one moved 

from Blue Hole to Cottonwood Ranch Sandpit (a distance 

of 10 km), and one emigrated from Broadfoot–Newark West 

to the Garrison Reach (not shown) of the Missouri River (a 

distance of 749 km) for a mean distance of 380 km ± 523 km 

(SD). With the exception of the least tern who immigrated to 

the Missouri River, all other hatch year dispersal events were 

to sandpit habitat. Additionally, there were two least terns 

whose first nesting attempt was made at a site that was created 

during 2009–14 (Broadfoot–Kearney South, Cottonwood 

Ranch Sandpit).

There were nine adult least terns that nested in more than 

1 year, allowing us to investigate adult dispersal and philopatry (table 16). There were 10 instances in which an adult least 

tern could either switch to nest at a new location or remain 

at the previous location with the onset of a new year. In five 

(50 percent) of these instances, least terns returned to nest on 

the site where they had nested in a previous year. In the five 

instances terns remained at the same nesting site between 

years, the mean distance between the nest sites was 0.069 km 

± 0.023 km (SD). In the five instances least terns switched 

nesting sites between years, the mean distance between 

nest sites was 30 km ± 25 km (SD). In all cases, least terns 

switched between sandpit habitat nesting sites. There were two 

least terns that switched from nesting at a preexisting nest site 

to a nest site that was created during 2009–14 (Blue Hole to 

Leaman East [Sandpit] and Lexington Sandpit to Cottonwood 

Ranch Sandpit). 

Piping Plovers.—There were 12 piping plover chicks that 

hatched from the Central Platte River Valley and were subsequently documented on nests as adults (table 17). Three of 

the 12 piping plover chicks were either captured or observed 

nesting the first year after hatch, 7 the second year after hatch, 

and 2 the third year after hatch. All piping plovers returned 

to nest on different sites from the one on which they hatched. 

The mean distance between hatch location and a first documented nesting location was 29 km ± 16 km (SD). First nest 

attempts by after hatch-year dispersing birds were documented 

on seven different sites. With the exception of a single individual that dispersed from a hatch site on sandpit habitat (Blue 

Hole) to a first nesting site on the river (Cottonwood Ranch 

PRRIP Island), all individuals dispersed from hatch sites on 

sandpit habitat to nesting sites on sandpit habitat. Additionally, 

there were 7 piping plovers whose first nesting attempt was 

made at a site that was created during 2009–14: 3 nested at 

Broadfoot-Kearney South, 2 nested at Dyer Sandpit, 1 nested 

Table 15. Central Platte River Valley hatch sites and sites where 

a first nesting attempt was observed for four uniquely identifiable 

least terns marked and resighted/recapture during 2009–14.

[n, total number of individuals]

Hatch site First nesting site n

Blue Hole Blue Hole 1

Blue Hole Cottonwood Ranch Sandpit 1

Broadfoot–Kearney South Broadfoot–Kearney South 1

Broadfoot–Newark West Garrison Reach, 

Missouri River

1

Total: 4
Results 19

Table 16. Dispersal of uniquely marked least terns in the Central Platte River Valley during 2009–14.

[ne, total number of events; ni, total number of individuals]

Nest site (dispersed from) Nest site (dispersed to) ne ni

Blue Hole Blue Hole 2 2

Blue Hole Leaman East (Sandpit) 1 1

Broadfoot–Kearney South Broadfoot–Kearney South 2 2

Broadfoot–Kearney South Broadfoot–Newark West 1 1

Broadfoot–Kearney South Leaman East (Sandpit) 1 1

Dyer Sandpit Cottonwood Ranch Sandpit 1 1

Dyer Sandpit Dyer Sandpit 1 1

Lexington Sandpit Cottonwood Ranch Sandpit 1 1

Total: 10 10

Table 17. Central Platte River Valley hatch sites and sites where a first nesting attempt was observed 

for uniquely identifiable piping plovers marked and resighted/recapture during 2009–14.

[n, total number of individuals]

Hatch site First nesting site n

Blue Hole Broadfoot–Kearney South 1

Blue Hole Cottonwood Ranch PRRIP Island 1

Blue Hole Dyer Sandpit 2

Blue Hole Lexington Sandpit 1

Broadfoot–Newark West Paulsen’s Lexington Pit 1

Johnson Sandpit Broadfoot–Kearney South 1

Lexington Sandpit Blue Hole 3

Lexington Sandpit Broadfoot–Kearney South 1

Lexington Sandpit Cottonwood Ranch Sandpit 1

Total: 12

at Cottonwood Ranch Sandpit, and 1 nested at Cottonwood 

Ranch PRRIP Island. 

There were 36 adult piping plovers that nested in more 

than 1 year (table 18). There were 45 instances in which an 

adult plover could either switch to nest at a new location or 

remain at the previous location with the onset of a new year. 

In 39 of these cases (87 percent), the adult nested on the same 

site as its prior documented nesting attempt and in 6 of these 

instances the adult switched to a new nesting location between 

years. Mean distance moved between nest sites for the 

39 cases was 0.085 km ± 0.097 km (SD). In the six instances 

in which the adult nested on a different site from its prior 

documented nesting attempt, the distance moved between nest 

sites for these birds was 21 km ± 15 km (SD). In all cases, 

piping plovers switched between sandpit habitat nesting sites. 

There were two plovers that switched from nesting at a preexisting nest site to a site that was created during 2009–14 

(Blue Hole to Broadfoot–Newark West, Johnson Sandpit to 

Broadfoot–Newark West).

Renesting

Least Terns.—There were no renests observed among 

the 84 nests initiated by uniquely marked least terns during 

2009–14 and no renests documented among the 83 uniquely 

marked least terns observed nesting during the same study 

period (table 19). 

Piping Plovers.—Out of the 111 nests initiated by at 

least 1 uniquely marked piping plover, there were 15 renests 

documented (14 percent; table 20). Of these 15 renests, 7 

(47 percent) were initiated following the termination of a nest 

that was either ‘successful’ (that is, hatched at least 1 chick) 

or ‘probably successful’, 6 (40 percent) were initiated following the failure of a nest, and 2 were initiated following the 

termination of a nest of unknown fate. There were 13 (87 percent) renests fated as either successful or probably successful, 

1 renest that failed, and 1 renest with an unknown fate. 
20 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 18. Dispersal of uniquely marked piping plovers in the Central Platte River Valley during 

2009–14.

[ne, total number of events; ni, total number of individuals]

Nest site (dispersed from) Nest site (dispersed to) ne ni

Blue Hole Blue Hole 11 8

Blue Hole Broadfoot–Newark West 1 1

Blue Hole Johnson Sandpit 1 1

Broadfoot–Kearney South Broadfoot–Kearney South 6 5

Broadfoot–Newark West Broadfoot–Newark West 2 2

Cottonwood Ranch Sandpit Broadfoot–Kearney South 1 1

Cottonwood Ranch Sandpit Cottonwood Ranch Sandpit 1 1

Dyer Sandpit Dyer Sandpit 10 7

Dyer Sandpit Johnson Sandpit 1 1

Johnson Sandpit Blue Hole 1 1

Johnson Sandpit Broadfoot–Newark West 1 1

Johnson Sandpit Johnson Sandpit 1 1

Lexington Sandpit Lexington Sandpit 8 6

Total: 45 36

Table 19. Number of successful, failed, and unknown fate nests and renests attended by at least one uniquely identifiable least tern in 

the Central Platte River Valley during 2009–14.

[Renests are denoted with parentheses]

2009 2010 2011 2012 2013 2014 Total

Success 0 6 2 8 17 25 58

Fail 0 1 0 1 7 9 18

Unknown 2 0 1 0 3 2 8

Total 2 7 3 9 27 36 84

Of the 75 uniquely marked piping plovers that were 

observed nesting during this period, there were 13 individuals documented renesting at least once (17 percent). Of the 

13 birds that renested, 5 (38 percent) of them initiated renests 

on nesting habitat that was created during 2009–14, whereas 

8 (62 percent) of them initiated renests at existing nesting 

habitat (that is, nesting habitat that existed before 2009; see 

table 1). All first nests and renests were initiated on sandpit 

nesting habitat. In all but one case, piping plovers renested at 

the same site as the first nest initiated that season. The bird 

that moved between sites initiated its first nest at Blue Hole 

and its second nest at Broadfoot-Newark West, a straight-line 

distance of approximately 36 km. This renesting event also 

represents a within-season movement to a ‘younger’ nesting 

location. The mean distance, however, that the bird moved 

between first and second nests was 0.073 km ± 0.06 (SD) for 

birds that stayed on the same site. For birds that renested, the 

mean initiation date of the first nest was May 6 and the mean 

initiation date of the second nest was June 8. On average, 

renests were initiated 7.5 days ± 7.3 (SD) following the date 

the initial nesting attempt was ‘fated’ (that is, considered either 

failed or hatched).

Migratory, Winter, and other non-Central Platte 

River Valley Resightings of Piping Plovers

There were 34 uniquely identifiable piping plovers and 

no uniquely identifiable least terns reported at sites that were 

not part of the Central Platte River Valley during the breeding season. Wintering grounds sightings accounted for 21 

of the reports, with 16 reports coming from the Texas Coast 

(not shown) and 5 coming from Florida (not shown) (4 from 

the Gulf Coast and 1 from the Atlantic Coast; fig. 8). These 

reports included 11 from within critical habitat units (4 in 

Florida, 7 in Texas).
Results 21

There were 13 reports of birds banded in the Central 

Platte River Valley from 7 other known nesting areas 

(table 21). These included five sites in Nebraska and two 

out-of-state sites: John Martin Reservoir in Colorado (not 

shown) and the Lewis and Clark Lake in South Dakota (not 

shown). There were 19 piping plovers observed in the Central Platte River Valley that were originally banded in other 

locations. Thirteen piping plovers were originally banded on 

other breeding areas (7 on the Lower Platte River and 6 on 

the Missouri River in South Dakota). The remaining six birds 

were originally banded on the wintering grounds so their 

breeding ground affiliation is unknown. Two of the six birds 

were originally banded in Alabama (not shown) and four were 

originally banded in Texas (not shown).

Table 20. Number of successful, failed, and unknown fate nests and renests attended by at least one uniquely identifiable piping 

plover in the Central Platte River Valley during 2009–14.

[Renests are denoted with parentheses]

2009 2010 2011 2012 2013 2014 Total

Success 4 8 5 (2) 10 (4) 15 (2) 27 (5) 111 (13)

Fail 1 0 1 5 4 2 (1) 40 (1)

Unknown 5 3 1 7 (1) 2 0 25 (1)

Total 10 11 7 (2) 22 (5) 21 (2) 41 (6) 176 (15)

Figure 8. Wintering ground observations of piping plovers uniquely marked in the Central Platte River Valley, 2009–14.
22 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

Table 21. Breeding locations for uniquely identifiable adult piping plovers originally banded in the Central Platte River Valley.

[--, no data]

State Location 2010 2012 2013 2014 Total

Colorado John Martin Reservoir -- -- -- 1 1

South Dakota Lewis and Clark Lake -- 3 -- -- 3

Nebraska Lake McConaughy -- -- -- 3 3

Nebraska Loup River 1 -- -- 1 2

Nebraska Lower Platte River -- -- -- 1 1

Nebraska North Platte -- -- -- 1 1

Nebraska Niobrara River -- -- 2 -- 2

Total: 1 3 2 7 13

Discussion

Demographic data collected through mark-recapture 

and nest monitoring during 2009–14 allowed the estimation 

of vital rates for Central Platte River Valley breeding least 

terns and piping plovers in relation to environmental factors and place them in the context of the larger Great Plains 

(not shown). 

Reproductive Success

Estimates of daily nest survival rates for both species 

were similar to estimates reported for off-river estimates 

reported for the Lower Platte River population of nesting least 

terns and piping plovers. During 2009–14, the geometric mean 

estimate for the daily survival probability of off-river least tern 

nests was 0.967 for the Lower Platte River population (Brown 

and others, 2009, 2010, 2011, 2012, 2013, 2014). Daily survival rates of 0.974 were estimated for least terns nesting in 

similar habitat type during 2009–14. The cumulative survival 

probability of survival from nest initiation to hatch for least 

tern nests initiated in the Central Platte River Valley (0.59) 

was lower than that of nests initiated on engineered sandbars 

(0.70) on the Gavin’s Point Reach but higher than that of tern 

nests initiated on natural sandbars (0.37) along the same reach 

(Stucker and others, 2013; Shaffer and others, 2013). During 

2009–14, the geometric mean estimate for the daily survival 

probability of off-river piping plover nests was 0.982 for 

the Lower Platte River population (Brown and others, 2009, 

2010, 2011, 2012, 2013, 2014). Daily survival rates of 0.988 

were estimated for piping plovers nesting in similar habitat 

type during 2009–14. These daily nest survival estimates 

were similar to those reported by Catlin and others, (2011) for 

piping plover nests on engineered sandbars (0.99 95-percent 

CI: 0.88–1.00) and on natural sandbars (0.98 95-percent CI: 

0.80–1.00) occurring along the Gavin’s Points Reach of the 

Missouri River during 2005–07. 

Daily survival of least tern chicks hatched in the Central 

Platte River Valley (0.960) during 2009–14 was higher than 

those reported for chicks hatched on off-channel habitat in 

the Lower Platte River during 2009–14 (0.844) (Brown and 

others, 2009, 2010, 2011, 2012, 2013, 2014). The estimates of 

daily chick survival rates for least terns in the Central Platte 

River Valley were well within published estimates of daily 

chick survival for least terns hatched on the lower Mississippi 

River in Missouri (Dugger and others, 2000) and alkaline habitat in northwestern Oklahoma (Schweitzer and Leslie, 2000). 

Daily survival of piping plover chicks hatched in the Central 

Platte River Valley (0.961) during 2009–14 were slightly 

higher (although within the 95- percent CI) than those reported 

for chicks hatched on off-channel habitat in the Lower Platte 

River (0.932) during 2009–14 (Brown and others, 2009, 2010, 

2011, 2012, 2013, 2014). Estimates of daily plover chick survival in the Central Platte River Valley were lower than those 

estimated for plover chicks hatched on Lewis and Clark Lake 

(Missouri River) during 2010 (0.984 ± 0.006 SE; Hunt and 

others, 2013) but fell within the range of age-specific daily 

survival values (0.86–0.98) reported for chicks hatched on 

the Gavin’s Point Reach of the Missouri River during 2006–9 

(Catlin and others, 2013). 

Year and age-dependent variation in daily survival rates 

for least tern nests and chicks were estimable from data collected during 2009–14, but not for piping plovers. It is possible that there were annual or age-specific differences in piping 

plover survival rates, but that sample size restricted the ability 

to detect this variation. Least tern nest and chick survival was 

correlated with the age of the site class they were associated 

with, with nest survival at older sites associated with higher 

nest survival and lower chick survival. There was no relationship between site age class and plover chick and nest survival, 

but this was most likely due to the low sample size (ntern-nests = 

181 compared to nplover-nest = 59). Results for the Central Platte 

River Valley were different than what was described for piping 

plover nesting on engineered sandbars on the Missouri River, 

where nest success, although higher on engineered sandbars 

than natural sandbars, appeared to decrease with age of the 

sandbar (Catlin and others, 2011).
Discussion 23

Colonization

Least terns initiated more nests than piping plovers at 

sites with newly available nesting habitat. However, for both 

species, the number of nests found at a created site increased 

with the age of the site (that is, the number of years in which 

nesting habitat was available). A similar pattern was observed 

for piping plover nests initiated on newly engineered sandbars on the Gavin’s Point Reach of the Missouri River during 

2005–7 (Catlin and others, 2011). There were not any uniquely 

marked least terns that nested on newly created nesting habitat 

in the first year it was available, and only two that were ever 

detected nesting on newly created habitat. Both of the marked 

plovers of known age that nested at a site in the first year of 

its availability were first year breeders, as were all the marked 

individuals of known age that were resighted. Catlin (2009) 

documented first year nesting piping plovers were more likely 

to colonize natural sandbars along the Missouri River with low 

nesting densities rather than newly engineered sandbars with 

higher nesting densities despite the preference of after-firstyear nesters for engineered sandbars. In line with this observation, the proportion of first year nesters was determined 

to decrease the longer the created nesting habitat was available. Similar to Catlin (2009), we interpret this as suggesting 

inexperienced piping plovers are better able to colonize newly 

available habitat because of lack of competition. From a management standpoint, these observations suggest that hatch-year 

colonization of new breeding habitat is potentially an important demographic process for piping plovers and that years 

following high fledgling production may have good potential 

for establishing breeding pairs on new sites.

Apparent Survival of Juveniles and Adults

There are few published estimates of the annual apparent 

survival probability for adult least terns; however, estimates of 

annual adult apparent survival probability (0.42) in the Central 

Platte River Valley are lower than those reported for interior 

least terns nesting in the lower Mississippi River valley (0.85 

95-percent CI: 0.73–0.95; Renken and Smith, 1995b) and 

California least terns (Sternula antillarum browni) nesting 

on Venice Beach, California (0.81 95-percent CI: 0.72–0.87; 

Massey and others, 1992). There are even fewer estimates 

available for the survival of juvenile least terns in their hatch 

year owing primarily to the low natal site fidelity; Massey and 

others, (1992) reported an annual apparent survival for juvenile California least terns of 0.16 (95-percent CI: 0.13–0.18). 

The estimate of 0.14 (95-percent CI: 0.04–0.41) reported 

here was similar to this estimate and consistent with known 

juvenile least tern behavior. Apparent survival estimates, 

although corrected for imperfect detection, are confounded by 

survival and site fidelity. It is more than likely that apparent 

survival estimates associated with Central Platte River Valley 

least terns are lower than other reported estimates because 

least terns are moving outside of the study area (that is, to 

unmonitored nesting habitat) between years. The fact that 

one of the four least terns marked as chicks and observed in a 

year following their hatch, emigrated out of the Central Platte 

River Valley to nest along the Missouri River in North Dakota, 

demonstrates such movement is possible (note: this least tern 

movement was excluded when estimating Central Platte River 

Valley apparent survival). 

The estimate of annual apparent survival for adult piping 

plovers nesting in the Central Platte River Valley (0.76) was 

in line with other published estimates for adult piping plovers 

in the Great Plains (0.72 ± 0.04 SE, Brown and others, 2014; 

0.73 95-percent CI: 0.64–0.79, Catlin and others, 2014). The 

estimates of annual apparent survival for juvenile piping plovers in the Central Platte River Valley (0.20) was lower than 

that reported by Catlin and others, (2014) for the Gavin’s Point 

Reach of the Missouri River (0.33 95-percent CI: 0.27–0.39) 

and by Brown and others, (2014) for the Lower Platte River 

(0.47 ± 0.13). All estimates for juvenile piping plover survival, however, were fairly imprecise (that is, wide confidence 

intervals associated with estimates) making it difficult to determine if there were real differences. Juvenile piping plovers 

disperse farther distances between years than do previously 

nesting adults (Amirault-Langlais and others, 2014), thus they 

have a higher probability of moving outside of a study area. 

Because mortality and permanent emigration are confounded 

in estimates of apparent survival, if juveniles are moving out 

of a study area and not resighted, this will appear as a lower 

estimate of apparent survival. The Tern and Plover Partnership 

(Lincoln, Nebr.), which is responsible for monitoring areas 

along the Lower Platte River, monitors an area larger than the 

Central Platte River Valley, is more likely to observe juvenile 

piping plovers that disperse far distances, and thus this region 

is less likely to suffer permanent emigration of juveniles 

(LeDee and others, 2010). 

Dispersal and Philopatry

Natal dispersal and philopatry patterns were different 

between least terns and piping plovers. Only four least terns 

that were hatched and banded in the Central Platte River 

Valley were observed nesting as adults. Despite such a small 

number, there was a great degree of variability in the behavior 

of these four individuals. Two of these birds returned to their 

natal site for their first documented nesting attempt, a third 

moved to a different site that was still within the Central Platte 

River Valley, whereas the fourth left the Central Platte River 

Valley to breed along the Missouri River in North Dakota. 

There is little known about least tern natal fidelity other than 

it is low, which our handful of observations seems to support (Renken and Smith, 1995a). None of 12 piping plovers 

that returned to breed in a year following their hatch were 

observed nesting at their natal site, and only three were actually observed nesting as first year individuals. Piping plovers 

not only disperse farther as juveniles (Amirault-Langlais and 

others, 2014), but juveniles also do not necessarily breed 
24 Demographics and Movements of Least Terns and Piping Plovers on the Central Platte River, Nebraska

in their first year even if they return to a breeding location 

(Saunders and others, 2014). Although dispersal distances 

for juvenile piping plovers were highly variable, the mean 

dispersal distance (29 km) was similar to published estimates 

from Atlantic Canada (28 km, Amirault-Langlais and others, 

2014) and higher than the estimate from Manitoba/Minnesota 

(8–12 km; Haig and Oring, 1988), which in both cases also 

were highly variable. 

Between-year dispersal distances for the nine adult least 

terns for which we had multiple years of nesting data also 

were highly variable (30 km ± 25 km, for five occasions in 

which least terns moved nesting sites). These results are in 

line with previously reported patterns for the dispersal of 

least terns; in a study of lower Mississippi River nesting least 

terns, Renken and Smith (1995a) reported that 97 percent of 

adult least terns returned to a site within 9 km of the site they 

were originally banded at as a nesting adult. Adult piping 

plovers appear to have a flexible dispersal strategy; in cases 

where habitat is stable or reproductive success is high they 

demonstrate site fidelity and low dispersal distances (Rioux 

and others, 2011; Amirault-Langlais and others, 2014). Where 

nesting habitat is dynamic or when reproductive success is 

low, however, piping plovers are more likely to disperse to 

new nesting areas (Rioux and others, 2011; Roche and others, 

2012; Roche and others, 2014). During 2009–14, Central 

Platte River Valley nesting adult plovers exhibited relatively 

high site fidelity (87 percent) for the species, which is in line 

with what would be expected for a system that is either stable 

or saturated. Since there appears to be nesting habitat available 

in the Central Platte River Valley that goes unused by piping 

plovers, it is more likely that the high nest fidelity exhibited by 

Central Platte River Valley nesting plovers is due to the relative stability of the system and past reproductive success.

Renesting

There was no renesting documented among uniquely 

marked least terns during 2009–14. Since least terns have 

been documented renesting in other Great Plains populations 

(Toy and others, 2016, unpublished data, U. S. Geological 

Survey) and California least terns are known to renest (Massey 

and Atwood, 1981), it is likely that least terns renest, but not 

enough uniquely marked individuals have been monitored 

over a sufficiently long enough period to document these 

events. However, 15 percent of the nests initiated by uniquely 

marked plovers were renests. Close to one-half (47 percent) 

were actually initiated after the first nest was considered to 

have hatched. Renesting in least terns has primarily been 

reported following nest loss during early or mid-incubation 

(Claassen and others, 2014). There was a high degree of 

variability in the number of days between the fating of a nest 

and the initiation of a renest (7.5 days ± 7.3 days). This is 

consistent with the results of Claassen and others, (2014), 

who reported a relatively short interval when nests were lost 

immediately following initiation (approximately 4 days) but 

longer when nests were lost during mid-incubation (approximately 8 days). 

Migratory, Winter, and other non-Central Platte 

River Valley Resightings of Piping Plovers

The banding program in the Central Platte River Valley is successful in providing understanding of linkages 

between the Central Platte River Valley and other breeding 

and wintering areas. Although a bird may carry a marker that 

was applied on a given unit of habitat, it would be inaccurate to assume that bird will remain associated with the same 

habitat unit or subpopulation for the remainder of its life. 

The results reported here illustrate the diversity of breeding 

locations where birds originally banded on the Central Platte 

have been observed (four river systems in Nebraska and three 

reservoirs in Nebraska, South Dakota, and Colorado; locations not shown). Other than during the catastrophic Missouri 

River flood year of 2011, breeding season resightings outside 

of the Central Platte River Valley were estimated to constitute 

5–15 percent of the banded population of piping plovers in 

the Central Platte River Valley in any given year. This is not 

a trivial percentage, although it is unknown to what extent 

these birds supplement breeding populations in other areas. 

Several of these sightings are from areas where information 

on demographic rates and movements is lacking (John Martin 

Reservoir, Lake McConaughy, Loup River, Niobrara River; 

locations not shown). 

Resighting data from this study also suggest that birds 

from other breeding populations immigrate into the Central 

Platte River Valley, although these immigration rates are more 

difficult to estimate. Based on information reported here, 

known source populations for birds seen on the Central Platte 

include the Missouri River and the Lower Platte River. Other 

source populations also may be represented but cannot be 

conclusively determined because the birds were banded on the 

wintering grounds. Nonetheless, the resighting data indicate 

that there is nontrivial exchange of breeding birds between the 

Central Platte River Valley and several other areas within the 

southern part of the midcontinent breeding range.

Information Needs

The Platte River Recovery Implementation Program’s 

stated objectives indicate that measures of reproductive 

success, dispersal, colonization rate of habitats by local and 

immigrant birds, and renesting patterns of adults are key to 

evaluating management actions and making future decisions 

about implementation. The current (2015) research program is 

consistent with these information needs and has provided new 

insight into connections between units of Central Platte River 
References Cited 25

Valley habitat as well as connections between the Central 

Platte River Valley and other habitat areas.

Several metrics of ongoing importance appear when 

reflecting on PRRIP’s objectives and the data outputs from 

the productivity research program. Counts of fledging-age 

chicks can be used to indicate productivity, but counts of 

unmarked birds can be inaccurate because of movements, 

double-counting, and other issues. An approach using individually marked young chicks and mark-resight techniques 

can estimate detection probability and survival rate, leading to 

more accurate estimates of the number of fledged young produced. Because this approach is dependent on having marked 

young, it also indicates the importance of a nest monitoring 

approach that provides an ability to count and band newly 

hatched young.

The number of breeding adult birds is an important metric for use in understanding the future viability of the population. Breeding population size can be estimated from nest 

monitoring data, following some basic assumptions about nest 

chronology, renesting patterns, and the conditions in which an 

active nest represents a breeding pair of adults. Supplementing 

a rigorous nest monitoring program with adult mark-resight 

work can provide additional insight into breeding populations 

and also can inform other closely related demographic processes. For example, colonization rates, dispersal patterns, and 

the roles of local birds compared to emigrant and immigrant 

birds are important metrics that can be best achieved through 

mark-resight work.

In addition to understanding demographic processes 

of least terns and piping plovers in the Central Platte River 

Valley, it is clear that the members of PRRIP are interested in 

information on how the bird populations interact with populations in other parts of the breeding range. There is reasonably 

complete information on the general breeding range of piping 

plovers in the northern Great Plains, but little information on 

how the various breeding areas are interconnected. In short, 

there is little certainty whether the system operates as a series 

of independent breeding populations or as one large exchanging metapopulation. Preliminary data from this study suggest 

there is substantial connectivity between breeding population units in the southern part of the range, but there is little 

indication that the northern and southern ranges are strongly 

connected. Continuation of mark-resight work on the Central 

Platte River Valley in concert with work on other breeding 

areas would enable these relations to be better understood.

Continued mark-resight work with least tern and piping 

plover chicks and adults on the Central Platte River Valley has 

many potential benefits to the science needs of PRRIP. Such 

benefits include synergy with ongoing efforts on other breeding areas, a greater understanding of how regional populations 

operate, science that supports Adaptive Management for Central Platte River Valley decision making, and measures of biological parameters that are relevant to the Program’s priorities. 

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Roche and others—Demographics and Movements of Least Terns and Piping Plovers in the Central Platte River, VAlley Nebraska—OFR 2016–1061

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20161061