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

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.