Tropical winter habitat limits reproductive success on the temperate breeding grounds in a migratory bird

Abstract

Identifying the factors that control population dynamics in migratory animals has been constrained by our inability to track individuals throughout the annual cycle. Using stable carbon isotopes, we show that the reproductive success of a long-distance migratory bird is influenced by the quality of habitat located thousands of kilometres away on tropical wintering grounds. For male American redstarts (Setophaga ruticilla), winter habitat quality influenced arrival date on the breeding grounds, which in turn affected key variables associated with reproduction, including the number of young fledged. Based on a winterhabitat model, females occupying high-quality winter habitat were predicted to produce more than two additional young and to fledge offspring up to a month earlier compared with females wintering in poorquality habitat. Differences of this magnitude are highly important considering redstarts are single brooded, lay clutches of only three to five eggs and spend only two-and-a-half months on the breeding grounds. Results from this study indicate the importance of understanding how periods of the annual cycle interact for migratory animals. Continued loss of tropical wintering habitat could have negative effects on migratory populations in the following breeding season, minimizing density-dependent effects on the breeding grounds and leading to further population declines. If conservation efforts are to be successful, strategies must incorporate measures to protect all the habitats used during the entire annual cycle of migratory animals.

Climatic effects on breeding grounds are more important drivers of breeding phenology in migrant birds than carry-over effects from wintering grounds

“…To conclude, we have demonstrated that despite the potential for impacts of climate change on wintering grounds to carry over and affect reproductive decisions [26], when averaged across a range of long-distance migrants the rsbl.royalsocietypublishing.org Biol Lett 9: 20130669 magnitude of such effects appears small relative to the influence of climate on breeding grounds. However, if future climate change degrades overwintering conditions more than those on breeding grounds, then carry-over effects could become more important through time.…”

Prioritizing tropical habitats for long-distance migratory songbirds: an assessment of habitat quality at a stopover site in Colombia

“…The contrasting rates of fuel deposition in Tennessee Warblers, for example, suggest that birds fueling in shade coffee must either stay longer than those in forest or depart the study site with less energy. Either way, this implies that the temporal (time spent at stopovers) and/ or the spatial (number and location of stopover sites) organization of migration can vary with stopover habitat, with likely fitness costs mediated through carry-over effects (Norris et al 2004, Harrison et al 2011. It was previously shown that Gray-cheeked Thrush stopping over for 12-14 days in the SNSM accumulate sufficient energy reserves to undertake a migratory flight > 2500 km, allowing them to overfly the Caribbean Sea to the southern United States (Bayly et al 2013).…”

Predicting the consequences of carry-over effects for migratory populations

“…Stable-carbon isotopes (d 13 C) values of redstarts indicate the type of habitat occupied during the non-breeding season (Marra et al 1998) and signatures in red-blood cells of individuals upon arrival at the breeding grounds can be used as an indicator of the winter habitat quality. Using path analysis, Norris et al (2004) found that G1 s.d. change in d 13 C values was equivalent to G1 s.d.…”