In late December 2023 we went to Argentina to observe cliff swallows on the wintering grounds for the first time. We targeted Iberá National Park and surrounding wetlands in Corrientes Province of northeastern Argentina where cliff swallows were known to occur. The birds do not breed there, but instead roost in the extensive marshes of the region and spread out to feed over prairies and ranch land during the day.
The expedition consisted of Charles Brown, Valerie O’Brien, Catherine Page, and two superlative guides, Giselle Mangini and Facundo Gandoy, without whom we could not have done the trip. We spent 28 December to 6 January in that region, observing cliff swallow foraging flocks. Not being tied to nesting sites, the birds were harder to find than anticipated, but we still observed over 25 separate groups during the visit. The region in general reminded us of our study area in western Nebraska. The Corrientes region we visited was relatively close to where one of our banded Nebraska birds was recovered in 1991, so we were possibly observing some of the birds from our study area!
Also, in January a monograph on our long-term foraging studies was published. This paper details the major changes that have occurred in social foraging and information transfer in cliff swallows over the last 40 years. Cliff swallows now are more likely to forage for insects solitarily or in smaller groups, spend less time foraging, are more successful as solitaries, feed in more variable locations, and engage less in information transfer at the colony site. The total mass of insects brought back to nestlings per parental visit has declined over the study. The diversity of insect families captured increased over time, and some insect taxa dropped out of the diet, although the three most common insect families have remained the same. The reason(s) for the reduction in social foraging and information transfer over time are unclear, but the consequence is that colonial nesting may no longer offer the same fitness advantages for cliff swallows as in the 1980’s.
The Ecological Monographs paper highlights how Cliff Swallow Project research contributes to important and frequently overlooked areas of animal ecology and evolution through exhaustive data collection and continued monitoring in the same area for over 40 years. We are providing empirical evidence of how changing conditions can drive behavior, which can then lead to evolutionary changes in relatively short amounts of time.