Smaller distance between nest contents and cavity entrance increases risk of ectoparasitism in cavity‐nesting birds

Abstract

Determining costs associated with nest‐building behaviour and nest characteristics is of prime importance to understand the evolution of such extended phenotypic traits. We explored a cost of nest building experimentally to determine whether large nests attracted more ectoparasites. This cost may be especially important to cavity‐nesting species where larger nests likely reduce the distance between nest contents and the cavity entrance, making the host nest more vulnerable to ectoparasite detection. We manipulated the amount of nest material and the distance between nest and cavity entrance and estimated the abundance of ectoparasites (Carnus hemapterus flies) before and after manipulation in nests of spotless starlings Sturnus unicolor breeding in nest boxes. Nest size was enlarged and elevated in a first group of nests by adding nest material to the base of the nest (enlarged nests); a second group of nests was elevated with a piece of plastic but without adding nest material (elevated nests); a third group of nests was not manipulated (control nests). Number of flies per nest increased significantly in enlarged and elevated nests compared to control nests. Moreover, distance to cavity entrance after manipulation was negatively associated with the increase in the number of flies per nest (i.e. nests closer to the entrance had more parasites). Thus, nest size, through its effect on distance between nest and cavity entrance, affected fly abundance. Cues produced by nest contents located closer to the cavity entrance may be detected more readily by ectoparasitic flies searching for hosts. These results suggest a novel constraint for the evolution of nest size in cavity‐nesting birds.

Overwinter users of nest cavities affect breeding birds via nest‐dwelling ectoparasites

“…During the breeding season of 2020, we weekly checked nest boxes to follow hoopoe reproduction. When nestlings were 13 days old, we estimated parasitic loads (number of Carnus per nestling), following Tomás et al (2020; see detailed methods in Appendix S1).…”

Nest site selection and productivity of a critically endangered parrot, the great green macaw (Ara ambiguus), in an anthropogenic landscape

“…Choosing the physical characteristics of nest sites is one of the few ways individuals can counter common threats such as predation (Stojanovic et al, 2017) and parasitism (Tomás et al, 2020). For many parrot species, predation accounts for a significant proportion of nest failure (Berkunsky et al, 2016; Pizo et al, 2008; Renton and Salinas-Melgoza, 2004).…”

“…These characteristics have been shown to have a significant positive influence on productivity in the Eclectus parrot ( Eclectus roratus ) (Heinsohn, 2008) and scarlet macaws ( Ara macao ) (Olah et al ., 2014). This may be because deep cavities offer greater protection against parasites (Tomás et al ., 2020), or higher cavities have a better field of vision to detect predators (White, Brown and Collazo, 2006). It follows that breeding at low-quality sites is often associated with lower productivity (e.g.…”

Combining social information use and comfort seeking for nest site selection in a cavity-nesting raptor

“…the European kestrel, Falco tinnunculus, Mingju et al 2019). Third, in contrast, individuals may avoid nesting on top of old nest material due to the higher risk of infection by ectoparasites and pathogens surviving in nest material across years (Rendell & Verbeek, 1996), and to avoid infection by ectoparasitic flies seeking out hosts (Tomás, Ruiz-Castellano, Ruiz-Rodríguez, & Soler, 2020). Moreover, avoidance might also be selected for when reoccupying an old nest entails a higher risk of predation (e.g.…”