The effect of climate change on avian offspring production: A global meta-analysis

Significance Numerous studies have shown that climate change has altered avian timing of breeding. However, little is known about climate-driven changes in offspring production. We collected long-term breeding data on 201 populations of 104 bird species (N = 745,962 clutches) from all continents, between 1970 and 2019, to assess temporal changes in annual offspring production by female breeders in relation to changes in local temperatures and species’ life history traits. Overall, offspring production declined over time, but responses of different populations to rising temperatures were diverse. Our analyses suggest that negative effects of rising temperatures on offspring production will mainly affect migratory and larger-bodied species, whereas smaller-bodied sedentary species may benefit from warmer climate. Abstract Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to reproductiv