Demography of Common Swifts (Apus apus) breeding in the UK associated with local weather but not aphid biomass

Abstract

In common with many other insectivorous birds, the Common Swift Apus apus is undergoing population declines, with an estimated 57% reduction in abundance between 1995 and 2017 in the UK. The ultimate drivers of this decline are poorly understood but links have been drawn to reductions in the abundance and availability of insect prey, as well as loss of nesting sites. The aim of this study is to improve understanding of the demographic and environmental drivers of Swift decline in Great Britain, with a particular focus on weather and aphid biomass. We explore spatio‐temporal trends in the biomass of aphids, an important source of food for these aerial feeders, from a network of 17 suction‐traps, each 12.2 m in length. We then use data from national nest recording and ringing schemes to describe temporal trends in, and covariates of, Swift breeding success and annual survival. Demographic data are sparse prior to the mid‐1990s but show stable adult survival, a reduction in first‐year survival and an increase in nest failure rate since the mid‐1970s. Despite marked declines in aphid biomass across much of southern and eastern England during this period, we find no association between aphid biomass and Swift demography. Weather was a stronger correlate of variation in Swift demography, with increased precipitation associated with smaller brood size, higher nest failure rate and lower first‐year survival. Our data suggest that falling first‐year survival, partly linked to wetter summers, may be the most likely demographic driver of population decline. Given that the only convincing correlates of Swift demography were weather‐related, we suggest it would be precautionary for conservation efforts to continue to focus on ensuring that safe and productive nesting sites are in sufficient supply. Further research to identify habitats and land management practices which provide foraging resources, particularly during periods of inclement weather, is required, and future demographic modelling exercises would benefit from increased nest recording and ringing efforts.

Trait‐specific sensitive developmental windows: Wing growth best integrates weather conditions encountered throughout the development of nestling Alpine swifts

“…Previous results on common swifts (Apus apus) show similar negative effects of cold and rainy days documented in northern European populations (Finch et al, 2023;Rajchard et al, 2006;Thomson et al, 1996), whereas, in a southern European population, light rain and colder days had positive effects (Sicurella et al, 2015). These contrasting results indicate that the effects of meteorological conditions, such as daily rainfall and temperature, on a given bird species can vary from one climatic region to another, for example, with cold, rainy days having negative effects in temperate regions and positive effects in Mediterranean regions where it rarely rains or cools down during the breeding season.…”

Does the Provisioning of Artificial Nest Cups and Nesting Structures Help House Martins Delichon urbicum?

“…Full explorations of the factors limiting House Martin populations should especially include the abundance of aerial arthropod food (Newton 2004, Nebel et al 2010, Hallmann et al 2014 and their availability, e.g. in relation to weather (Finch et al 2023), and monitor changes in demographic parameters that were not assessed in this study (notably the number of fledged young). Finally, by way of practical advice, we now know that artificial nests will help House Martins on some soils (i.e.…”

Population links between an insectivorous bird and moths disentangled through national‐scale monitoring data

“…uk/ our-work/ natio nal-bat-monit oring -progr amme) that provide counts of abundance over multiple years at national-scales. These schemes offer the opportunity to link changing abundance of important insect prey to population change of higher trophic levels (Finch et al, 2022;Martay et al, 2023) at broad spatial and temporal scales. Here, we utilize two national monitoring schemes (the Breeding Bird Survey and Rothamsted Light Trap Network) to estimate the effect of moth abundance on population change in the blue tit Cyanistes caeruleus, an insectivorous bird that preys upon lepidopteran larvae, particularly during the breeding season (Betts, 1955;Cholewa & Wesołowski, 2011;Naef-Daenzer et al, 2000;Naef-Daenzer & Keller, 1999;Shutt et al, 2020).…”