Rainy and warm weather improve growth of insectivorous (but not granivorous) grassland birds

What is it about?

Weather conditions drive a lot of nature processes. Rain and temperature modulate the growth of plants, the metabolism of insects, and the activity of the biggest vertebrates. Nestling growth of birds can be affected by weather fluctuations too. In general, it is expected that higher temperatures favor growth because it improves the availability of insects that nestlings eat and accelerates metabolism of younger birds that are not fully feathered. Also, rain is supposed to reduce the foraging efficiency of adult birds that need to feed their young. However, most of these patterns have been described in insectivorous cavity-nesting birds in temperate forests. We investigated if these patterns hold true in two grassland birds with contrasting nestling diets and therefore potentially different responses to weather: the Hellmayr’s Pipit (an insectivorous passerine) and the Grassland Yellow-Finch (which feeds its nestlings exclusively with seeds) in central-eastern Argentina. We found that minimum daily temperatures and abundant rainfall produced bigger nestlings for the Pipit, but not for the Finch. The dietary contrast between these species may explain the different results. Arthropod activity and abundance can be affected by weather variations within the span of a breeding season, whereas seeds may depend on conditions from previous years.

Featured Image

Photo by Harshit Suryawanshi on Unsplash

Photo by Harshit Suryawanshi on Unsplash

Why is it important?

Smaller fledglings can have reduced chances of survival after leaving the nest. Hence, Pipit populations could be impacted if they experience cold and dry conditions during their breeding season. This is of great concern in the current context of climate change, as the frequency of extreme weather events is expected to increase, and the timing of birds' breeding seasone could be missmatched with their ideal weather conditions.

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