Rasing hatchlings to fledging can be very demanding for songbirds, especially during cold, wet years in the Arctic. New research led by the University of California-Davis, suggests that impending climate change will not make things any easier for some northern nesting birds.
Interested in learning more about nestling growth rates may be affected based on food abundance and weather in the Arctic, researcher Jonathan Pérez and colleagues monitored a total of 58 songbird nests along the North Slope of Alaska's Brooks Range. For two years, researchers tracked 110 white-crowned sparrow nestlings, which have a broad breeding range, and 136 Lapland longspur nestlings, which are an Arctic breeding specialists.
Pérez, who has a background in studying parental energy expenditure and incubation, predicted that nestlings would grow faster in warmer, drier conditions; that clutches of eggs laid earlier in the breeding season would be more successful; and that the nestlings of specialist longspurs would grow faster than the generalist sparrows.
"When I became involved in our project based out of Toolik Lake looking at effects of inter-annual variation across trophic levels and how that ultimately plays out in terms of reproductive success of songbirds, expanding to an examination of nestling growth rates with regards to variation in environmental conditions seemed like a logical next step," Pérez said.
Climate change is known to take a great toll on bird species all around the world. Previous studies have found declines of up to 90 percent in some bird populations, with migratory, mountain, island, wetland, Arctic, Antarctic and seabirds suffering the greatest.
Tracking the birds confirmed what UC-Davis researchers had hypothesized all along. Overall growth rates were higher in 2013 compared to 2014, which was a much colder and wetter year. Furthermore, there were also fewer arthropods - the birds' primary food source - available in 2014.
Compared to sparrow nestlings, longspurs grew faster both years; however, sparrows appeared to be unaffected by temperature. This, researchers say, is likely because sparrows nest in shrubs and are shielded from changing weather conditions, rather than exposed to the elements on treeless, open tundra like the longspurs.
Researchers also confirmed that nestlings from clutches that were laid earlier grew faster than those from later clutches, since birds that arrived on their breeding grounds earlier were able to claim the best nesting spots to raise their young.
However, climate change is expected the bring new uncertainities for songbirds nesting in the Arctic. While climate models predict warmer temperatures in the Arctic, which will favor higher nesting growth rates, they also predict more frequent storms and increased precipitation. As a result, parent songbirds may be forced to put their needs over the care of their offspring in the face of extreme weather conditions. For example, there may not be enough food to go around, as researchers saw in 2014.
"Species at range edges are sentinels of climate change because they often experience high environmental variability and harshness," explained Daniel Ardia, an expert on the role of environmental variation in bird behavior and physiology from Franklin and Marshall College. "Pérez and his co-authors reveal the direct effects of weather variation on nestling growth, an important determinant of fitness, showing how climate variability might have strong negative effects of populations. What makes the study so compelling is that they were able to link weather variability to food supply showing the causal link between predicted weather variation and reproduction."
Their findings were recently published in The Auk: Ornithological Advances.
