Differences in incubation behaviour and niche separation of two competing flycatcher species

Abstract

Food availability sets the stage for incubation behaviour of a female bird and thereby indirectly determines the nest temperature, which in turn affects development and metabolism of avian embryos. Changes in development and metabolism in turn are known to influence offspring's ability to adjust to environmental changes later in life. However, few studies have investigated the role of interspecific differences in incubation behaviour in relation to niche separation between competing sibling species. We studied the effects of habitat quality (in terms of caterpillar availability) on incubation behaviour of two ecologically similar and closely related species, collared and pied flycatchers (Ficedula albicollis and F. hypoleuca), in their hybrid zone on the island of Öland, Sweden. Even though both species prefer caterpillar-rich deciduous forests as nesting sites, collared flycatchers, whose nestlings have higher energetic demands, are able to nest only in deciduous forests, whereas pied flycatchers have more flexible habitat requirements. Overall, higher food availability was associated with increased nest attendance, higher incubation temperature and a lower number of foraging trips across species. In addition, collared flycatchers had more frequent and shorter foraging trips across habitat types, allocated more heat to eggs and therefore maintained higher nest temperatures compared to pied flycatchers. We argue that the higher heat allocation or the need to maintain a higher nest temperature for embryo development may constrain collared flycatchers to focus on relatively more profitable prey. Our results highlight the importance of considering incubation behaviour in the context of understanding species differences in niche use. Significance statement Niche separation plays an important role in mitigating effects of competition between closely related species. Whether species differences in incubation behaviour relate to differences in niche use remains unknown. We compared incubation behaviour of two sympatric flycatcher species that differ in sensitivity to food availability. The competitively more dominant and larger species, the collared flycatcher, whose nestlings are more sensitive to food shortages, made more frequent foraging trips but allocated more heat to eggs, leading to higher nest temperature despite lower nest attendance, compared to pied flycatchers. These interspecific differences may be a result of differences in embryo sensitivity or female physiology and contribute to the niche separation between the species, which in turn can facilitate coexistence.

Low Heritability but Significant Early Environmental Effects on Resting Metabolic Rate in a Wild Passerine

“…We can therefore only speculate about the specific underlying mechanism. Incubation behaviour (Koski et al 2020), thyroid hormones (Hsu et al 2019) and yolk androgens (Rice et al 2013) are all important early-life maternal effects that have previously been shown to have long-lasting effects on offspring performance in studies of collared flycatchers. We therefore consider these maternal effects as likely candidate drivers to the observed early-life (i.e.…”

Effects of elevated nest box temperature on incubation behaviour and offspring fitness-related traits in the Collared Flycatcher Ficedula albicollis

“…Collared flycatchers on Gotland usually lay one clutch per year, consisting of six eggs on average (range 4-8 eggs) that hatch in the beginning of June. Females lay one egg per day and the incubation is expected to start at the day when the female has laid her final egg (Koski et al 2020). The first eggs are laid in the first half of May and incubation is undertaken solely by females.…”

Systematic review of avian hatching failure and implications for conservation

“…Perlut et al ., 2016) and/or prompting competition for resources leading to reduced nest attendance (e.g. Koski et al ., 2020) and parental condition (e.g. Ardia & Clotfelter, 2007).…”