Extrinsic factors, endocrine mechanisms, and behavioral indicators of migratory restlessness in wintering whooper swans (Cygnus cygnus)

Liangliang Yang,Torsten Wronski,Guogang Zhang,Ruyi Gao,Songlin Huang,Wendong Ru,Wenxia Wang,Desheng Kong,Ping Sun

doi:10.1038/s41598-021-92031-3

Abstract

Extrinsic factors, endocrine mechanisms, and behavioral indicators of migratory restlessness were studied in wintering whooper swans (Cygnus cygnus) in the Sanmenxia Swan National Wetland Park in western Henan Province, central China. First, the fecal glucocorticoid metabolite (FGM) concentration was established and related to mean air temperature or photo period (day length) using simple linear or non-linear regression models. After a model selection procedure, the best fitted model revealed that an increase of FGM concentration was associated with an increase in the squared mean air temperature (R2 = 0.88). Other models showed an increasing FGM concentration to correspond with increasing values of day length, squared day length, and mean air temperature—however without statistical support. In a second step, behavioral frequencies of seven behaviors were condensed into three behavioral principal components (PCs) using principal components analysis. Behavioral PCs largely corresponded to three activity phases described for wintering whooper swans in central China and were correlated with the FGM concentration using Spearman's rank-order correlations. Results revealed a significant correlation between FGM and behavioral PC2 (positive factor loadings from vigilance and preening, negative loading from foraging). Finally, we tested for an effect of behavioral PCs on changes in winter home range size using a set of multiple linear regression models. Results of averaged model parameter estimates showed only the behavioral PC3 (positive factor loadings from fighting and calling, negative loading from locomotion) had a marginal significant effect on home range size. Results confirmed findings of previous studies on migratory restlessness in whooper swans. However, due to the small sample size (N = 15 weeks) the effect of PC3 on home range size was weak and should be viewed with caution.

Highlights

Bird migration is an adaptation facilitating species to exploit resources in seasonally favorable areas and to increase their reproductive success
In a second step we examined whether the glucocorticoid concentration is related to changes in the activity budget, i.e., seven behavior variables, while in a third step we tested if such behavioral responses corresponded to changes in the home range size of whooper swans during the wintering period in the Sanmenxia Swan National Wetland Park
No significant relationship was observed between PC3 and the fecal glucocorticoid metabolite (FGM) concentration (r = 0.01, N = 15, P = 0.96) as well as between home range size and the FGM concentration (r = 0.15, N = 15, P = 0.59)

Summary

Introduction

Bird migration is an adaptation facilitating species to exploit resources in seasonally favorable areas and to increase their reproductive success. The Sanmenxia wetland is among the most important wintering grounds of whooper swans in China[37] and represents an ideal area to study adrenocortical responses to environmental changes such as temperature or photo period. We predicted that whooper swans would exhibit physiological responses, i.e., an increase of stress hormones (fecal glucocorticoid metabolite, FGM concentration), following temperature and day length changes throughout the wintering period. We used focal animal sampling and instantaneous scans, satellite tracking, and enzyme-linked immunosorbent assay (ELISA) to analyze the interactions between extrinsic factors, physiological stress responses and behavior changes of wintering whooper swans

Methods

Results

Conclusion