Nesting phenology of migratory songbirds in an eastern Canadian boreal forest, 1996–2020

Abstract

The migration phenology of many bird species has changed over the past few decades, but whether such changes lead to changes in the nesting phenology remains little known. Studying bird nesting in the boreal forest comes with challenges because of the large size of this biome. We evaluated songbird nesting phenology for the past 25 yrs in a boreal forest in eastern Canada, Forêt Montmorency. We used the observation of food transport in adults as an index of parental status, considering the imperfect detection of this status through hierarchical models of site occupation. We estimated annual phenology as the Julian date of the inflection point of the logistic fit of proportion of sites with parental activity as a function of Julian date. Contrary to expectations related to the advance of spring migration in North America, models did not show an advancement in the nesting season. Models showed that passerines can move their nesting date back or forward by 1 to 9 d. Models suggested that short-distance migrants delayed their nesting date by 2 wks against 1 mo for long-distance migrants. These results show the capacity of songbirds to adjust their nesting time and remind us of the value of regional studies when we are interested in reproductive phenology.