New 50-year study offers insight into effects of climate on bird reproduction

New 50-year study offers insight into effects of climate on bird reproduction

Birds are one of the most remarkable species on earth. However, their numbers have been declining rapidly in recent years. Scientists have long suspected that climate change has been one of the major contributors to this decline. A new study, reported in the Proceedings of the National Academy of Sciences, has assessed changes in the reproductive output of 104 bird species around the world between 1970 and 2019. The study reveals that a warming climate appears to have more worrisome effects on larger birds and migratory birds than on smaller, sedentary species. This article will explore the findings of this study and provide an overview of the effects of climate change on bird reproduction.

What is unique about the study?

This study explored potential effects of global climate change, in particular, warming, on offspring production for over 100 species from more than 200 bird populations across all continents. The researchers looked at data for each of these bird populations over 15 to 49 breeding seasons to consider whether changes in local temperatures and precipitation were associated with changes in the average number of offspring produced per female per year.

Beyond the effects of a warming climate on individual species’ reproductive output, the study also considered whether climate change may affect offspring production by interacting with other attributes of the birds. Such traits include body mass, migration status, habitat needs, human impacts to local landscapes, the protection/conservation status of sites, and whether the birds can produce two broods in a single breeding season. The temporal and spatial scales of this work and the number of species and populations studied were monumental.

What were the main findings?

The study found that across the 201 populations of wild birds, offspring production generally declined in recent decades. However, there is a lot of variability among populations and species. Increasing local temperatures during the chick-rearing part of the breeding season tended to decrease offspring production in most migratory birds but increased the number of young produced in many small birds and in sedentary birds, which don’t migrate.

Warming temperatures were also associated with less offspring production among relatively large birds. These changes were not necessarily caused directly by climate change but by the effects of climate change on the life histories and ecological traits of species that influence clutch size and rates of nesting failure over time.

What are some examples of species with increasing or decreasing reproductive output over time?

Species with the largest decreases in offspring production included Montagu’s harriers and white storks, both of which are large, migratory birds; bearded vultures, which are large and non-migratory; roseate terns, which are moderate-sized, migratory birds; common house martins, which are small and migratory; and red-winged fairywrens, which are small, non-migratory, and endemic to Australia.

Species with increased offspring production included the Bulwer’s petrel, a medium-sized migratory bird, and the Eurasian sparrowhawk, a small migratory raptor; along with Eurasian wrynecks, collared flycatchers, and prothonotary warblers, all of which are small and migratory.

Some species, like the barn swallow, had increasing numbers of offspring in one locale but declines elsewhere. This shows that even though the planet is warming overall, the effects of global warming on local weather and temperatures can vary considerably across a species’s breeding range.

Does this mean that large-bodied and migratory species are most at risk?

Large-bodied species seemed particularly vulnerable to decreases in offspring production in the past five decades. Climate change-related warming likely exacerbated the problem for sedentary species weighing more than 1.0 kilogram and migratory species weighing more than 50 grams. Larger species may be less able to adapt to a changing climate because they tend to live a slower pace of life, have lower reproductive rates, and require more resources to sustain their bodies. Migratory birds, on the other hand, face additional challenges as they rely on timing their migration with the availability of food and nesting sites in different locations throughout the year. However, the study also found that small-bodied and sedentary species are not immune to the effects of climate change on their reproductive output.

life, have lower reproductive rates, and require more resources to sustain their bodies. Migratory birds, on the other hand, face additional challenges as they rely on timing their migration with the availability of food and nesting sites in different locations throughout the year. However, the study also found that small-bodied and sedentary species are not immune to the effects of climate change on their reproductive output.

It is important to note that the study did not explore other potential impacts of climate change on bird populations, such as changes in habitat or food availability. Therefore, the findings should not be used to predict the future of bird populations in their entirety, but rather provide a piece of the puzzle in understanding how climate change may affect bird reproduction.

Overall, the study highlights the urgent need to address climate change and its effects on biodiversity. It is crucial to take action to mitigate the impact of climate change on bird populations, and more broadly on ecosystems, to prevent irreversible damage to our planet’s natural heritage.