Nest‐boxes alter the reproductive ecology of urban cavity‐nesters in a species‐dependent way

Abstract

To mitigate the shortage of natural breeding sites in cities, nest-boxes are provided for cavity-nesters. However, these are not the breeding sites these animals originally evolved in and optimised their breeding performance to. It thus remains inconclusive if nest-boxes can provide adequate substitutes, ensuring equivalent fitness returns for breeding animals. Additionally, the majority of knowledge on the ecology of urban birds comes from nest-box populations, but no study to date directly compared fitness consequences of breeding inside nest-boxes in relation to natural-cavities in an urban context. This limits our understanding of the urban ecology of cavity-nesters and addressing its functional meaning. We investigate fitness consequences and life-history trait variation according to the nesting site type to provide a comprehensive understanding of conservation potential of nest-boxes in cities and to support/question generalisations stemming from nest-box studies on urbanization. We directly compare the reproductive performance of two small passerines, blue tits and great tits, breeding in nest-boxes as opposed to natural-cavities in a seminatural forest of a capital city using a quasi-experimental setting. We show that the effects of nest type vary between species: in blue tits, fitness proxies were negatively affected by nest-boxes (lower fledging success and fledgling numbers, longer time spent in nest and later fledging date in comparison to natural-cavities), while great tit performance appeared to be unaffected by nest type. We detected that both species breeding in nest-boxes accelerated incubation onset, but since there were no major differences in pre-hatching traits (lay date, clutch size, hatching rates) between the nest types, we attribute the fitness deterioration to post-hatching effects. Interestingly, overall breeding density of tits in urban natural-cavities was higher than observed in a primeval habitat. Nestboxes may become an ecological trap for some species and the unaffected species can consequently outcompete them, decreasing overall biodiversity in cities. We highlight the ecological importance of oldgrowth tree stands, providing natural tree cavities for city-breeding animals. Due to the detected nest type-dependent variation in reproductive performance, we support the criticism regarding the 3 unconditional extrapolation of evolutionary and ecological interpretations of nest-box studies to general populations. Supporting InformationNest-boxes alter the reproductive ecology of urban cavity-nesters in a species-dependent way

Plumage colouration differs between offspring raised in natural cavities and nestboxes

“…Importantly, the small distance ascertained that the plots were functionally identical as they shared the same environmental patch. Accordingly, Sudyka et al (2022a) found no difference in food availability between study plots in both field seasons, assesses by widely used method of frass fall collection (Wesołowski & Rowiński, 2014). Ambient temperature and humidity as well as anthropogenic factors (noise and air pollution, measured as PM 2.5 concentration) were found to be uniform between study plots (Sudyka et al, 2022b).…”

“…However, as nonsignificant, it was dropped from all models. In the final models, the following variables of biological relevance were always retained: cavity type, parental colour metrics (to quantify parent-offspring correlations), nestling sex and year (differences in weather conditions and food availability between two study seasons, (Sudyka et al, 2022a). Other factors (parental age, lay date, clutch size, nestling mass), if nonsignificant, were removed from the models in backward elimination procedure (Quinn & Keough, 2022).…”

“…The shortage of old forest stands is often compensated by providing nestboxes, readily used by some birds, e.g., the great tit (Parus major) or the blue tit (Cyanistes caeruleus) (Mänd et al, 2005). In a scientific context, nestbox provisioning enables the acquisition of larger sample sizes than in studies of birds breeding in natural cavities (Maziarz et al, 2017;Sudyka et al, 2022a;Wesołowski, 2011). Coupled with facilitated nest monitoring and experimental manipulations (Lambrechts et al, 2010), this leads to a situation where the bulk of ecological research on cavity nesters is conducted on populations breeding in nestboxes.…”

“…Coupled with facilitated nest monitoring and experimental manipulations (Lambrechts et al, 2010), this leads to a situation where the bulk of ecological research on cavity nesters is conducted on populations breeding in nestboxes. However, natural cavities and nestboxes differ in terms of cavity dimension (Purcell et al, 1997;Sudyka et al, 2022a), microclimatic conditions (Duckworth et al, 2017;Maziarz et al, 2017;Sudyka et al, 2022b) , parasite pressure (Fargallo et al, 2001;Wesołowski & Stańska, 2001), and predation risk (Czeszczewik, 2004;Kuitunen & Aleknonis Antanas, 1992;Maziarz et al, 2017;Purcell et al, 1997). Consequently, conclusions stemming from nestbox-breeding populations of birds whose entire evolutionary history is associated with natural cavities, may have limited relevance.…”

“…Consequently, conclusions stemming from nestbox-breeding populations of birds whose entire evolutionary history is associated with natural cavities, may have limited relevance. This problem has been pointed out in the past (e.g., Møller, 1989, Lambrechts et al 2010, Wesołowski 2011, which further inspired comparative research on birds breeding in both artificial and natural breeding sites (Czeszczewik, 2004;Norris et al, 2018;Purcell et al, 1997;Sudyka et al, 2022a). Surprisingly, a topic that has not been examined to date in this context is that of offspring plumage colouration, otherwise remaining in the centre of researchers' attention (Biard et al, 2017;Drobniak et al, 2013;Isaksson et al, 2006;Peters et al, 2007;Tschirren et al, 2003).…”