Reproductive responses of two related coexisting songbird species to environmental changes: global warming, competition, and population sizes

Abstract

Comparative analyses of interspecific differences in response to climate change can provide important insights into the factors initiating seasonal onset of reproduction in various species and subsequent fitness consequences. We present a comparative analysis based on a 30-year breeding survey of two related migratory songbird species [Reed Warbler Acrocephalus scirpaceus (RW) and Great Reed Warbler A. arundinaceus (GRW)], which coexist in reedbeds by means of various interspecific interactions. The RW advanced breeding by 15 days and shortened its breeding time window, which is a combined effect of higher temperatures, alleviated competition as a consequence of population declines in the dominant GRW, and reduced RW population. Although the breeding period of GRW changed only slightly, its clutch initiation was likewise related to temperature. Most probably, advanced breeding in RW is favoured by changes in food supply and accelerated reed growth, which provides the necessary nest concealment earlier, whereas this does not affect the GRW, a species less vulnerable to nest predation. Clutch size decreased later in the season, so that earlier breeding produced a net increase in both species. An additional increase of clutch size in GRW can be explained by the use of higher-quality territories in today's smaller population. The main causes of nest losses were predation in RW and adverse weather in GRW, but reproductive success increased over the study period in both species, which was a consequence of larger clutches in RW, but of favourable weather during rearing and fewer total losses in GRW. Our results document that different causal mechanisms are involved in the reproductive changes of the two congeneric species living in the same habitat: RW breeding earlier by making use of competitive release and other ecological improvements, and GRW by benefiting from better rearing conditions. As species respond differentially to climate change depending on ecosystem and biotic interactions, predictions of population dynamics will remain vague until the specific response mechanisms have been elucidated.

Effect of climatic change on the duration of the breeding season in three European thrushes

“…Crick (Schaefer et al 2006), the Polish population did not shift its end, causing an extension of the breeding season (Halupka et al 2008). A different pattern was reported by Weatherhead (2005) in a study on Red-winged Blackbirds Agelaius phoeniceus .…”

“…Given that there is a strong within-season decline in clutch size among bird species (Crick et al 1993), our data suggest that the Fieldfares' increase in mean brood size is caused by shifting its entire breeding season toward earlier dates, while in Song Thrushes the decline is driven by extending its breeding season with many late small-clutched broods. A long-term increase in brood size has been found in other open-nesting species, for example, Red-backed Shrikes Lanius collurio (Hušek & Adamík 2008), Eurasian Reed Warblers Acrocephalus scirpaceus and Great Reed Warblers Acrocephalus arundinaceus (Schaefer et al 2006, but see Halupka et al 2008).…”

Inferring species interaction networks from species abundance data: A comparative evaluation of various statistical and machine learning methods

“…several Acrocephalus warblers: 25 (Schäfer et al, 2006;Rolando and Palestrini, 1991), and a triangle of interacting Sylvia warblers: S. borin/S. atricapilla/S.…”

Conditions at autumn stopover sites affect survival of a migratory passerine

“…On the other hand, a higher productivity of offspring related to climate-driven favourable conditions on the breeding grounds may counterbalance this effect. For example, studies of two populations of Reed Warblers from central Europe (Schaefer et al 2006;Halupka et al 2008) revealed that increased temperatures observed in recent years during the breeding season were correlated with a higher number of nestlings produced by breeding pairs. However, as various recent estimations of population trends for the Reed Warbler have produced equivocal results (Ockendon et al 2012(Ockendon et al , 2014Vickery et al 2014, Inger et al 2015, further detailed studies are needed.…”