Abstract
Climate warming has altered phenologies of many taxa [1, 2], but the extent differs vastly between [3,4] and within trophic levels [5-7]. Differential adjustment to climate warming within trophic levels may affect coexistence of competing species, because relative phenologies alter facilitative and competitive outcomes [8, 9], but evidence for this is scant [10, 11]. Here, we report on two mechanisms through which climate change may affect fatal interactions between two sympatric passerines, the resident great tit Parus major and the migratory pied flycatcher Ficedula hypoleuca, competing for nest sites. Spring temperature more strongly affected breeding phenology of tits than flycatchers, and tits killed more flycatchers when flycatcher arrival coincided with peak laying in the tits. Ongoing climate change may diminish this fatal competition if great tit and flycatcher phenologies diverge. However, great tit density increased after warm winters, and flycatcher mortality was elevated when tit densities were higher. Consequently, flycatcher males in synchronous and high-tit-density years suffered mortality by great tits of up to 8.9%. Interestingly, we found no population consequences of fatal competition, suggesting that mortality predominantly happened among surplus males. Indeed, late-arriving males are less likely to find a partner [12], and here we show that such late arrivers are more likely to die from competition with great tits. We conclude that our breeding population is buffered against detrimental effects of competition. Nevertheless, we expect that if buffers are diminished, population consequences of interspecific competition may become apparent, especially after warm winters that are benign to resident species. VIDEO ABSTRACT.
Highlights
We studied pied flycatcher fatalities in great tit nest boxes in a Dutch population between 2007 and 2016
We show how fatal interactions between a migratory and a resident bird species are affected by climate change, because their phenologies are differentially affected by temperature and because winter warming increases the abundance of the competitively superior resident bird
We collected egg-laying-initiation data of great tits and pied flycatchers in our population by doing nest-box checks every 5 days, which can be backdated as passerines normally lay one egg per day
Summary
We studied pied flycatcher fatalities in great tit nest boxes in a Dutch population between 2007 and 2016. Pied flycatchers are long-distance migrants that each year travel between Western Africa and Europe [16], whereas great tits are a resident species that breed on average 16.6 days (from 7.3 to 22.9) earlier than flycatchers in our population. Fatal competition for nesting cavities with tits when flycatchers arrive has been described in previous studies [10, 17, 18], but little is known about whether climate change modulates such interactions, for example by eliciting differential phenological responses or by affecting winter survival of resident species. We collected egg-laying-initiation data of great tits and pied flycatchers in our population by doing nest-box checks every 5 days, which can be backdated as passerines normally lay one egg per da
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