Birds Raise Fewer Young When Spring Arrives Earlier in A Warming World
Published:27 Jul.2023 Source:University of California-Los Angeles
A large collaboration led by scientists at UCLA and Michigan State University has found that birds produce fewer young if they start breeding too early or late in the season. With climate change resulting in earlier springlike weather, the researchers report, birds have been unable to keep pace. When it comes to raising their young, timing matters for birds. If they breed too early or too late, harsh weather could harm their eggs or newborns. But timing relative to food sources matters too: If birds are looking for food before or after its natural availability, they might not have the resources to keep their young alive.
While the majority of birds were adversely affected by variations in the start of spring, several species -- the northern cardinal, Bewick's wren and wrentit among them-countered the trend, demonstrating improved breeding productivity when spring began earlier. Those species are mostly non-migratory species that can respond more quickly to the emergence of spring plants that signal the start of the breeding season. But those species were the exceptions to the rule. Even most non-migratory species couldn't keep up with earlier spring arrivals. Overall, for every four days earlier that leaves appeared on trees, species bred only about one day earlier.
For migratory species, that discrepancy means that the time between when they arrive at their breeding sites and breeding itself is likely to get shorter as springlike conditions begin earlier. Birds need time to establish territories and prepare physiologically for egg-laying and rearing their young, so that change could cause even greater disturbances to reproduction.