Wildlife & Biodiversity

Birth rate of large, migratory birds declined due to climate change: Study

Declines in offspring production were observed in relatively large birds & migratory birds

By Susan Chacko
Published: Tuesday 02 May 2023
Larger-bodied species may respond slower to changing environmental and climatic conditions. Photo: iStock.

Climate change has reduced the overall birth rate of bird species across the world, a new study has found. The offspring production in bird populations has been declining over the past 50 years, said the study published in Proceedings of the National Academy of Sciences on May 1, 2023.

Researchers analysed 201 wild bird populations from all continents between 1970 and 2019 and found birth rate has declined during recent decades, with great variation among species and populations.

Declines in offspring production were observed in relatively large birds and migratory birds, whereas species whose production increased were small-bodied and sedentary. 

Also read: Wet end of 2021 leads to fewer migratory birds in Odisha’s Chilika this year

Climate change appears to influence changes in offspring production through complex interactions with ecological and life history traits of species, the research found.

“Body mass, both as a stand-alone predictor and in relation to climate change, was the most important correlate of temporal changes in clutch size and offspring production,” said the study led by Lucyna Halupka, University of Wrocław, Poland.

The research suggested that larger species were more vulnerable to declines in offspring production. Body mass exceeding one kilogram for sedentary species and 50 grams for migratory species is associated with adverse trends in offspring production.

Larger-bodied species may respond slower to changing environmental and climatic conditions due to their lower fecundity (ability to produce young) and extended maturation period.

Thus, climate variability is an important factor when coupled with migratory habits and the number of broods raised in the breeding season.

The researchers found that non-migratory species, especially smaller ones, can usually adjust to changes in local conditions and may benefit from climate warming. While migratory species, except the smallest, may suffer. 

The study aimed to look at the temporal changes in annual offspring production by female breeders in relation to changes in local temperatures and species’ life history traits.

Also read: World Migratory Birds Day: How are India’s winged guests doing

Some of the species with the largest decreases in offspring production included: Montagu’s harriers and white storks (large and migratory), bearded vultures (large, non-migratory), roseate terns (moderate-sized, migratory), common house martins (small, migratory) and red-winged fairywrens (small, non-migratory).

Species with increased offspring production included bulwer’s petrel (medium-sized, migratory), Eurasian sparrowhawk (small, migratory raptor) and Eurasian wrynecks, collared flycatchers and prothonotary warblers (small and migratory).

The researchers have been studying prothonotary warblers in southern Illinois since 1994. These warblers are small and migratory and breed in forested wetlands and swamps. The bird population experienced increasing offspring production over time, with more offspring per female when local temperatures were warmer, said Jeffrey Hoover from the University of Illinois in a press release.

This increase in reproductive output in warmer years occurred because the females started laying eggs earlier in the season, increasing their chances of producing two broods of chicks in a single breeding season.

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