Quantification of physiological aging criteria utilizing window strike data

Abstract

Recent studies have been interested in the effects of age on window strike vulnerability in avian species. To accurately assess age-dependent patterns in avian populations, proper aging criteria should be used to allow for comparisons across studies. Recent window strike studies rely heavily on skull ossification, and we were interested in the accuracy of this method compared to other physiological-based age determinations in passerines and non-passerine landbirds. In this study, we quantitatively analyzed three potential aging criteria that can be used for aging specimens: presence/absence of the bursa of Fabricius, skull ossification, and gonadal maturity. To our knowledge, this is the first quantitative comparison of these criteria. While one study did qualitatively compare the number of agreements versus disagreements between these methods, our study expands on this research by implementing a statistical approach. Skull, bursa, and gonad measurements all were significantly and positively correlated with each other. Nevertheless, we did find disagreement between the methods when further exploring their relationships using Generalized Linear Models. For example, when we compared the number of adult females with immature females to test for window strike vulnerability using a Chi-square test, all three aging criteria produced similar results. Adult females showed a statistically higher rate of window strikes than immature females. However, we still suggest caution using only one criterion to age specimens. In summary, while we did find these three aging characters to be highly correlated, disagreement does exist between these characters.