Climate anomalies affect annual survival rates of swifts wintering in sub‐Saharan Africa

Abstract

Several species of migratory swifts breed in the Western Palearctic, but they differ in reproductive traits and nonbreeding areas explored in Africa. We examined survival and recapture probabilities of two species of swifts by capture–mark–recapture data collected in northern Italy (Pallid Swift Apus pallidus in Carmagnola, Turin, and Common Swift Apus apus in Guiglia, Modena) in the breeding season (May–July). Apparent survival rates were relatively high (>71%), comparable to other studies of European swifts, but showed marked annual variations. We used geolocators to establish the exact wintering areas of birds breeding in our study colonies. Common Swifts explored the Sahel zone during migration and spent the winter in SE Africa, while the Pallid Swifts remained in the Sahel zone for a longer time, shifting locations southeast down to Cameroun and Nigeria later in winter. These movements followed the seasonal rains from north to south (October to December). In both species, we found large yearly differences in survival probabilities related to different climatic indices. In the Pallid Swift, wintering in Western Africa, the Sahel rainfall index best explained survival, with driest seasons associated with reduced survival. In the Common Swift, wintering in SE Africa, the El Niño–Southern Oscillation (ENSO) cycle performed significantly better than Sahel rainfall or North Atlantic Oscillation (NAO). Extreme events and precipitation anomalies in Eastern Africa during La Niña events resulted in reduced survival probabilities in Common Swifts. Our study shows that the two species of swifts have similar average annual survival, but their survival varies between years and is strongly affected by different climatic drivers associated with their respective wintering areas. This finding could suggest important ecological diversification that should be taken into account when comparing survival and area use of similar species that migrate between temperate breeding areas and tropical wintering areas.

Evolution of chain migration in an aerial insectivorous bird, the common swift Apus apus

“…Because smaller birds have lower absolute resource requirements and lower cost of transport (Pennycuick 1989), they may more successfully get through such periods, as compared to larger conspecifics. This scenario may apply to the northern part of both the breeding and the wintering ranges, where cold spells (breeding) and droughts (nonbreeding) may be frequent due to extreme weather events (Boano et al 2020), but needs to be confirmed by future studies. A third scenario may be, if there is strong competition for breeding sites in the south of the breeding range, larger individuals may have a competitive advantage to occupy and defend nest sites (Lack 1956), promoting early start of breeding as compared to small individuals.…”

The demography of an increasing insular Eurasian Scops Owl (Otus scops) population in western France

“…Interestingly, there was also a negative relationship between winter NAO and survival. The effects of NAO have recently been documented on survival of Palaearctic trans-Saharan migrants (Johnston et al 2016) but not in others (Boano et al 2020). We suspect that the negative association between winter NAO and the amount of precipitation and vegetation productivity in the Mediterranean and northwestern African regions (Stige et al 2006, Vicente-Serrano & Trigo 2011 partly explains this relationship.…”

“…Long-distance Afro-Palaearctic migratory insectivores have suffered higher declines than other insectivores (Bowler et al 2019) and it is suspected that climatic factors in the African wintering quarters have played a crucial role in these declines (Kanyamibwa et al 1989, Zwarts et al 2012, Norman & Peach 2013, Johnston et al 2016, Boano et al 2020. However, the population ecology of several farmland birds, and the demographic and ecological processes by which they are affected by farming practices and climate change, remain poorly known (Newton 2004, Morrison et al 2016).…”

“…An understanding of these processes is therefore urgently needed to aid in identifying and designing appropriate conservation actions to recover declining populations (Morrison et al 2016). Recently, increasing research efforts have been undertaken to decipher the demographic and ecological processes affecting the population dynamics of several long-distance Afro-Palaearctic migratory insectivorous birds (Morrison et al 2016, Boano et al 2020, Telenský et al 2020. However, our lack of knowledge and understanding still remains particularly acute for poorly known species such as owls, as most previous work has targeted passerines and waterbirds.…”

Wind-assisted sprint migration in northern swifts

“…Common swifts remain airborne during non-breeding (Hedenströ m et al, 2016), enabling a highly mobile lifestyle and exploration of ephemeral food resources (Å kesson et al, 2012;Wellbrock et al, 2017;Boano et al, 2020). The timing of movements is important with respect to food availability and winds (Å kesson and Helm 2020; Wellbrock et al, 2017;Boano et al, 2020;Å kesson et al, 2016) and involves limited periods of fueling prior to autumn migration (Å kesson et al, 2012). Although these swifts spend most of their nonbreeding year on the wing, their migrations are characterized by periods of relative geographic stasis (which we will call ''stopovers'') interspersed with periods of concerted directional flight.…”