A comparison of breeding population estimators using nest and brood monitoring data

Abstract

For many species, breeding population size is an important metric for assessing population status. A variety of simple methods are often used to estimate this metric for ground-nesting birds that nest in open habitats (e.g., beaches, riverine sandbars). The error and bias associated with estimates derived using these methods vary in relation to differing monitoring intensities and detection rates. However, these errors and biases are often difficult to obtain, poorly understood, and largely unreported. A method was developed to estimate the number of breeding pairs using counts of nests and broods from monitoring data where multiple surveys were made throughout a single breeding season (breeding pair estimator; BPE). The BPE method was compared to two commonly used estimation methods using simulated data from an individual-based model that allowed for the comparison of biases and accuracy. The BPE method underestimated the number of breeding pairs, but generally performed better than the other two commonly used methods when detection rates were low and monitoring frequency was high. As detection rates and time between surveys increased, the maximum nest and brood count method performs similar to the BPE. The BPE was compared to four commonly used methods to estimate breeding pairs for empirically derived data sets on the Platte River. Based on our simulated data, we expect our BPE to be closest to the true number of breeding pairs as compared to other methods. The methods tested resulted in substantially different estimates of the numbers of breeding pairs; however, coefficients from trend analyses were not statistically different. When data from multiple nest and brood surveys are available, the BPE appears to result in reasonably precise estimates of numbers of breeding pairs. Regardless of the estimation method, investigators are encouraged to acknowledge whether the method employed is likely to over-or underestimate breeding pairs. This study provides a means to recognize the potential biases in breeding pair estimates.

Modelling effects of nonbreeders on population growth estimates

“…Unfortunately, nonbreeder censusing is rarely considered in current monitoring programs (Citta, Reynolds & Seavy ; Rönkä et al . ; Baasch, Hefley & Cahis, ).…”

Nest-site selection by Interior Least Terns and Piping Plovers at managed, off-channel sites along the Central Platte River in Nebraska, USA

“…We used the Program's minimum habitat criteria (Platte River Recovery Implementation Program ) to determine the amount of nesting habitat available each year, and a breeding‐pair estimator to estimate numbers and densities of breeding pairs (Baasch et al. , Keldsen and Baasch ).…”

“…The 20 random points represented a sample of available locations with associated resources and, with the nest-site location, made up a "choice set" for each individual nesting event (Cooper and Millspaugh 1999). Choice sets of ≤ 20 random points have been found to be sufficient in other studies (McFadden 1978, Baasch et al 2009, Unger et al 2015. Each choice set was unique and linked by a likelihood function to the nestsite location using the strata feature in To reduce error and maintain consistency, aerial photographs (≤ 1-m resolution) taken during the nesting season by the USDA Farm Service Agency National Agriculture Imagery Program (NAIP imagery;2001 or the Platte River Recovery Implementation Program (2007Program ( -2015, and GPS locations of nests were used to determine the distances to the edge of water and the nearest possible predator perch.…”

“…We employed GAMs with penalized regression splines, which estimate degree of covariate smoothness with cross-validation. An assumption of discretechoice models is that individuals or groups of individuals make choices to maximize their satisfaction, mirroring assumptions of resource selection functions (Ben-Akiva and Lerman 1985), and these models have been applied to several wildlife resource selection studies (Cooper and Millspaugh 1999, Baasch et al 2009, Unger et al 2015. We used discrete-choice models because habitat conditions and availability changed and can be better captured within this framework (Cooper and Millspaugh 1999).…”

Interior Least Tern and Piping Plover nest and brood survival at managed, off-channel sites along the central Platte River, Nebraska, USA 2001-2015

“…Predator fencing and trapping have not occurred at Trust Wildrose East; however, the nesting area was completely moated by water. We used the PRRIP's minimum habitat criteria to identify suitable habitat at each site and determine the amount of nesting habitat available each year, and a breeding-pair estimator to estimate numbers and densities of breeding pairs (PRRIP 2012, Baasch et al 2015, Keldsen and Baasch 2017.…”