Experimentally broken faecal sacs affect nest bacterial environment, development and survival of spotless starling nestlings

Abstract

Nestlings of most avian species produce faecal sacs, which facilitate the removal of nestlings’ excrements by parents, thereby reducing proliferation of potentially pathogenic microorganisms and/or detectability by predators and parasites. The nest microbial environment that birds experience during early life might also affect their development and thus, faecal sacs facilitating parental removal may be a strategy to decrease bacterial contamination of nests that could harm developing nestlings. Here, we tested this hypothesis by experimentally broken faecal sacs and spreading them in nests of spotless starlings Sturnus unicolor, thereby avoiding their removal by adults. In accordance with the hypothesis, experimental nests harboured higher bacterial density than control nests. Nestlings in experimental nests were of smaller size (tarsus length) and experienced lower probability of survival (predation) than those in control nests. Moreover, nestlings in experimental nests tended to suffer more from ectoparasites than those in control nests. We discuss the possible pivotal role of bacteria producing chemical volatiles that ectoparasites and predators might use to find avian nests, and that could explain our experimental results in starlings.

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

“…Carnus hemapterus (hereafter 'Carnus') has important negative effects on nestlings (Hoi et al 2018) and is the most abundant ectoparasite in the spotless starling Sturnus unicolor population reported here (Avilés et al 2009, Azcárate-García et al 2019. Carnus is a 2-mm fly in which the adult is the blood-sucking stage, and is found in nests of an extremely wide diversity of birds (Brake 2011, Calero-Torralbo 2011).…”

Autoclaving Nest-Material Remains Influences the Probability of Ectoparasitism of Nestling Hoopoes (Upupa epops)

“…Thus, it is possible that the expected experimental effect on nest bacterial density was more easily detected at the egg stage. Contrary to most avian species [ 47 ], hoopoe parents do not remove fresh nestling feces from nests, which could produce an increase in bacterial density after hatching, as has been shown for starlings [ 21 ]. Bacterial samples were collected 4 days after the egg hatched and, thus, the effects of autoclaving nest-material could have been masked or diluted by the nestlings’ activity.…”

Antimicrobial capacity is related to body colouration and reproductive success in female spotless starlings

“…For instance, we know that, as the season progresses, temperature typically increases and relative humidity decreases in our population, and that these factors influence risk of hatching failure due to changing nest bacterial environment (Cook et al , Peralta‐Sánchez et al ) as it has been detected in magpies (Soler et al ). Moreover, breeding activity such as incubation or brooding (Cook et al , Peralta‐Sánchez et al , Soler et al ), ectoparasites (Tomás et al ), egg breakage (Soler et al ), or nestling faeces that parents sometimes fail to remove (Ibáñez‐Álamo et al , Azcárate‐García et al ), are known to affect bacterial environment of nests. Taken together, this evidence suggests that females experienced higher probability of microbial infection during the nestling period than before laying started.…”

“…Moreover, assuming that only animals in prime condition can mount strong immune responses, higher antimicrobial capacities should only be evident in individuals in better condition and overall phenotypic quality (Schmid‐Hempel ). Such individuals may also experience lower probability of pathogen transmission to offspring, thereby reducing negative effects on embryo (Cook et al ) and nestling development (Azcárate‐García et al ). Parent birds might transmit pathogenic microorganisms to their offspring while incubating, brooding or feeding nestlings.…”