Abstract
BackgroundAccurate nestling age is valuable for studies on nesting strategies, productivity, and impacts on reproductive success. Most aging guides consist of descriptions and photographs that are time consuming to read and subjective to interpret. The Western Bluebird (Sialia mexicana) is a secondary cavity-nesting passerine that nests in coniferous and open deciduous forests. Nest box programs for cavity-nesting species have provided suitable nesting locations and opportunities for data collection on nestling growth and development.MethodsWe developed models for predicting the age of Western Bluebird nestlings from morphometric measurements using model training and validation. These were developed for mass, tarsus, and two different culmen measurements.ResultsOur models were accurate to within less than a day, and each model worked best for a specific age range. The mass and tarsus models can be used to estimate the ages of Western Bluebird nestlings 0–10 days old and were accurate to within 0.5 days for mass and 0.7 days for tarsus. The culmen models can be used to estimate ages of nestlings 0–15 days old and were also accurate to within less than a day. The daily mean, minimum, and maximum values of each morphometric measurement are provided and can be used in the field for accurate nestling age estimations in real time.ConclusionsThe model training and validation procedures used here demonstrate that this method can create aging models that are highly accurate. The methods can be applied to any passerine species provided sufficient nestling morphometric data are available.
Highlights
Accurate nestling age is valuable for studies on nesting strategies, productivity, and impacts on reproductive success
For all three morphometric growth measurements, we developed models for age prediction using linear mixed models (LMM), model training, and model validation
The model selection process to determine whether the linear or quadratic model should be used for predicting nestling age are presented for each development variable (Table 1)
Summary
Accurate nestling age is valuable for studies on nesting strategies, productivity, and impacts on reproductive success. Quantitative measures of nestling growth and development are important for studying avian breeding biology and reproductive strategies (Amiot et al 2014). The ability to accurately age nestlings is an important aspect of avian ecology that yields insight into the effects of different nesting strategies on nest success Without an accurate way to estimate age, productivity can be overestimated or underestimated depending on the methodology used (Wails et al 2014) It is important for determining when nestlings can be banded (Murphy 1981; Costa et al 2020). Other examples of single opportunity sampling (i.e., only one chance to obtain data) are studies that rely on taking blood samples or sexing birds at certain ages
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