Context‐dependent conservation of the cavity‐nesting European Roller

Abstract

To maximize the effectiveness of conservation interventions, it is crucial to have an understanding of how intraspecific variation determines the relative importance of potential limiting factors. For bird populations, limiting factors include nest-site availability and foraging resources, with the former often addressed through the provision of artificial nestboxes. However, the effectiveness of artificial nestboxes depends on the relative importance of nest-site vs. foraging resource limitations. Here, we investigate factors driving variation in breeding density, nestbox occupation and productivity in two contrasting study populations of the European Roller Coracias garrulus, an obligate cavity-nesting insectivorous bird. Breeding density was more than four times higher at the French study site than at the Latvian site, and there was a positive correlation between breeding density (at the 1-km 2 scale) and nest-site availability in France, whereas there was a positive correlation between breeding density and foraging resource availability in Latvia. Similarly, the probability of a nestbox being occupied increased with predicted foraging resource availability in Latvia but not in France. We detected no positive effect of foraging resource availability on productivity at either site, with most variation in breeding success driven by temporal effects: a seasonal decline in France and strong interannual fluctuations in Latvia. Our results indicate that the factors limiting local breeding density can vary across a species' range, resulting in different conservation priorities. Nestbox provisioning is a sufficient short-term conservation solution at our French study site, where foraging resources are typically abundant, but in Latvia the restoration of foraging habitat may be more important.Conservation actions tend to focus on manipulating breeding season processes because these are generally the easiest to control, especially for migratory populations which often disperse over distant and disparate non-breeding sites (Finch et al. 2017). Understanding the factors which limit the breeding density or productivity of threatened species is therefore often crucial for their †

Nest box selection and reproduction of European Rollers in Central Italy: a 7-year study

“…Due to the severe threats currently affecting farmland bird species (Teillard et al 2015;BirdLife International 2017), proactive management activities that aim to halt the decline of habitat heterogeneity due to land consolidation and agricultural intensification in combination with an uncontrolled rural development, seem to be essential for protecting remaining roller populations at the European level (Finch 2016). At the same time, conducting studies at a local scale in different geographic areas within the species' distributional range, can help to understand which drivers primarily affect species' distribution and persistence over time and which conservation measures can be applied for effective management (Kiss et al 2014;Finch et al 2018). In this sense, an understanding of the relative importance of different limiting factors on population variation, and the mechanisms underpinning these, is crucial for conservation (Finch et al 2018).…”

“…At the same time, conducting studies at a local scale in different geographic areas within the species' distributional range, can help to understand which drivers primarily affect species' distribution and persistence over time and which conservation measures can be applied for effective management (Kiss et al 2014;Finch et al 2018). In this sense, an understanding of the relative importance of different limiting factors on population variation, and the mechanisms underpinning these, is crucial for conservation (Finch et al 2018).…”

“…Complete data for breeding pairs were not available for 2013 and 2014 However, the effectiveness of nest-boxes is maximised in areas where foraging resource availability is not a limiting factor. In a comparative study on two distant rollers populations, Finch et al (2018) demonstrated that factors driving variation in breeding density and nest-box occupancy were different between populations: the Latvian population was influenced by foraging resources availability while the French one mostly by nesting resources. This means that context-dependent conservation interventions may be necessary and might vary across the species' range where local populations might be limited by different factors.…”

“…Avilés and Costillo 1998;Gottschalk et al 2011). However, in any nest-box program, evaluating the effectiveness of the nest boxes is of paramount importance (Finch et al 2018). For example, unfavourable nest box locations or unproductive sites may slow the recovery of threatened populations (Gottschalk et al 2011).…”

“…Finally, since individuals of the same species may respond and adapt differently to local environmental characteristics and landscape features (Morelli 2013), we compared our results with published data from other European Rollers populations (i.e. Rodriguez et al 2011;Kiss et al 2014;Catry et al 2017;Finch et al 2018), in order to assess whether the species benefits from similar habitat characteristics at breeding grounds across the geographical range or if it adapts to different local environmental features/resources.…”