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.

对于诸多物种而言，繁殖种群规模（breeding population size）是评估种群现状的核心指标。针对在开放生境（如海滩、河漫滩沙洲）中筑巢的地面筑巢鸟类（ground-nesting birds），学界常采用多种简易方法估算该指标。采用此类方法得到的估算值所伴随的误差与偏差，会随监测强度（monitoring intensities）与检出率（detection rates）的差异产生变化。然而，这类误差与偏差往往难以量化、认知不足且鲜有公开报道。本研究开发了一种繁殖对估算方法（breeding pair estimator, BPE），其基于单次繁殖季内多次调查获得的巢窝与幼雏群计数监测数据，实现繁殖对数量的估算。研究通过基于个体的模型（individual-based model）生成的模拟数据，将BPE与两种常用估算方法进行对比，以评估其偏差与准确性。结果显示，BPE会低估真实繁殖对总数，但在检出率较低且监测频率较高的场景下，其整体表现优于另外两种常用方法。随着检出率提升与两次调查间隔的延长，最大巢窝与幼雏群计数法（maximum nest and brood count method）的表现逐渐与BPE趋近。研究还将BPE与四种常用繁殖对估算方法，应用于普拉特河（Platte River）的经验衍生数据集开展对比分析。基于模拟数据的结果表明，相较于其余方法，BPE的估算结果最接近真实繁殖对数量。尽管各测试方法得到的繁殖对数量估算值差异显著，但趋势分析得到的系数未呈现统计学意义上的显著差异。当可获取多次巢窝与幼雏群调查数据时，BPE能够生成较为精准的繁殖对数量估算结果。无论选用何种估算方法，研究人员均应明确说明所采用方法大概率会高估还是低估繁殖对数量。本研究提供了一种识别繁殖对估算值潜在偏差的可行途径。