Integrating Causal and Evolutionary Analysis of Life-History Evolution: Arrival Date in a Long-Distant Migrant

In migratory species, the timing of arrival at the breeding grounds is a life-history trait with major fitness consequences. The optimal arrival date varies from year-to-year, and animals use cues to adjust their arrival dates to match this annual variation. However, which cues they use to time their arrival and whether these cues actually predict the annual optimal arrival date is largely unknown. Here, we integrate causal and evolutionary analysis by identifying the environmental variables used by a migratory songbird to time its arrival dates and testing whether these environmental variables also predicted the optimal time to arrive. We used 11 years of male arrival data of a pied flycatcher population. Specifically, we tested whether temperature and normalized difference vegetation index (NDVI) values from their breeding grounds in the Netherlands and from their wintering grounds in Ivory Coast explained the variation in arrival date, and whether these variables correlated with the position of the annual fitness peak at the breeding grounds. We found that temperature and NDVI, both from the wintering and the breeding grounds, explained the annual variation in arrival date, but did not correlate with the optimal arrival date. We explore three alternative explanations for this lack of correlation. Firstly, the date of the fitness peak may have been incorrectly estimated because a potentially important component of fitness (i.e., migration date dependent mortality en route or directly upon arrival) could not be measured. Secondly, we focused on male timing but the fitness landscape is also likely to be shaped by female timing. Finally, the correlation has recently disappeared because climate change disrupted the predictive value of the cues that the birds use to time their migration. In the latter case, birds may adapt by altering their sensitivity to temperature and NDVI.

Plumage ornaments and reproductive investment in relation to oxidative status in the Iberian Pied Flycatcher (Ficedula hypoleuca iberiae)

A key aspect in the study of plumage traits with a potential role in communication is the cost associated with trait production and maintenance, expressed in terms of oxidative stress. In the Iberian Pied Flycatcher (Ficedula hypoleuca iberiae (Witherby, 1928)), males and some females exhibit a white forehead patch and both sexes present conspicuous white patches on the wings. We examined associations between these plumage ornaments and their ability to cope with oxidative stress. Furthermore, we explored oxidative costs of reproductive investment. Total antioxidant status (TAS) in plasma and glutathione (tGSH) levels in red blood cells, as well as a marker of oxidative damage in plasma lipids (malondialdehyde (MDA)), were assessed simultaneously for the first time in studies of avian reproduction. We found negative associations between antioxidants and ornaments in incubating females, although this relationship was positive while feeding nestlings. For males, MDA levels were negatively associated with ornaments, while TAS showed a positive relation. Female MDA showed a positive correlation with intensity of incubation attendance, while this relation was negative for tGSH levels. These results indicate that multiple achromatic plumage ornaments signal the individual capacity to cope with costs related to oxidative stress. Moreover, this study highlights the critical role of incubation for avian life histories.