Invertebrate prey availability limits reproductive success but not breeding population size in suburban House Sparrows Passer domesticus

Abstract

Factors affecting avian demography and abundance in urban landscapes are poorly understood and this hinders attempts to manage urban bird communities. Several recent studies indicate that lack of invertebrate prey in urban landscapes may constrain avian productivity and fitness relative to that in other habitats. House Sparrow Passer domesticus populations have undergone large declines in many European urban centres and inadequate reproductive success linked to invertebrate availability has been postulated as a potential cause of these declines. We conducted a replicated supplementary feeding experiment to test whether the availability of invertebrate prey limits the breeding success and adult abundance (colony size) of House Sparrows in suburban London, where House Sparrow populations declined by 60% during the decade preceding our study. Daily mealworm provision over two successive breeding seasons, sufficient to provide 82% of chick energy requirements of House Sparrow pairs nesting within 50 m of feeders, had a large positive impact on the abundance of recently fledged birds (+62%), but only a small positive impact, limited mainly to small colonies, on the overall abundance of territorial males. Colony growth was only weakly related to fledgling abundance in the previous year and did not appear to be constrained by nest‐site availability. Conservation interventions that enhance invertebrate availability for suburban House Sparrows may increase reproductive success but are unlikely, on their own, to lead to population growth or recovery.

Are house sparrow populations limited by the lack of cavities in urbanized landscapes? An experimental test

“…These differences in occupancy and breeding rates could also be explained by the size of the local house sparrow population at each site (von Post and Smith ). Occupancy rate of new cavities certainly depends on the number of cavities already available, but also on the number of sparrows that are looking for nesting cavities.…”

“…Although this decline has first been documented in the UK, it is now a widespread phenomenon in most European countries (i.e. in its native range, Murgui and Macias , De Coster et al ). Surprisingly, the causes of this decline remain poorly understood despite its importance and rapidity (De Laet and Summers‐Smith 2007).…”

“…Surprisingly, the causes of this decline remain poorly understood despite its importance and rapidity (De Laet and Summers‐Smith 2007). This sharp decline may be linked to multiple recent modifications of the urban environment, such as 1) an increased predation risk due to the recent rise in the numbers of European sparrowhawks and feral cats in cities, 2) an intensification of multiple sources of pollution (noise, light, electromagnetic, and air pollution), 3) a modification of food availability and food type, or 4) a change in the urban habitat with a reduction of habitat availability for house sparrows (Robinson et al , Liker et al , Shaw et al , Peach et al , 2018, Herrera‐Duenas et al , Meillère et al , Moudra et al ).…”

“…In this study, we evaluated the importance of cavity availability by experimentally increasing the number of cavities in several sites along an urbanization gradient (von Post and Smith ) ranging from very rural places (isolated farms) to moderately urbanized areas (town of medium size, i.e. 60 000 inhabitants).…”

A high incidence of non-cavity nesting in an introduced population of House Sparrows suggests that the species should not be constrained by cavity-nest site availability

“…Other papers that have aimed to characterise House Sparrow nesting only provide descriptive generalisations of nesting locations, isolated examples of rare/ unusual nesting sites, the frequencies of nests found in sought after locations, or the frequency of unoccupied, potential nest sites (e.g. Summers-Smith 1958;Heij 1985;Imboma 2014;Peach et al 2015;Nath et al 2016). For example, a study from urban India (Guwahati) found that the majority of House Sparrow nests were in rolling shutters, and close to walls associated with a pipe (Nath et al 2016), however the study did not consider or sample vegetation as potential nesting sites at all.…”