Cosmetic coloration of cross-fostered eggs affects paternal investment in the hoopoe (Upupa epops)

Abstract

The signalling hypothesis suggests that avian eggshell coloration is a sexually selected female signal advertising her quality to its male partner, thereby stimulating his provisioning rate. This hypothesis has been tested for structural eggshell pigments, but not for cosmetic colorations, such as that produced by the uropygial secretion on eggshells. During the breeding season, female hoopoes ( Upupa epops ) host in their uropygial glands symbiotic bacteria. Females actively smear the eggshells with their secretion, protecting embryos from pathogenic trans-shell infections and changing eggshell coloration. Because the colour of the secretions is related to their antimicrobial potential, cosmetic eggshell coloration may act as a cue or even as a post-mating sexually selected signal if it affects male provisioning rates. To experimentally test this hypothesis, we cross-fostered already-smeared clutches between hoopoe nests, and quantified male feeding behaviour to females before and after the experiment. This approach allows disentanglement of the effects of female quality and of egg coloration on male investment. In accordance with the hypothesis, males adjusted their provisioning rate to the eggshell cosmetic coloration. This is, to our knowledge, the first experimental demonstration that egg colour stained with uropygial secretion could act as a post-mating sexual signal of female quality to males.

Food supply and provisioning behavior of parents: Are small hoopoe nestlings condemned to die?

“…During the incubation and hatching periods (i.e., 7–8 days after the first egg hatched), the females rarely leave the nests and are mainly fed by the males ( Díaz-Lora et al 2020 , 2021 ), who infrequently enter into the nests ( Cramp, 1985 ). Thus, during the first 10 days after hatching the first eggs, the period when most brood reduction occurs ( Hildebrandt and Schaub 2018 ), females have to decide, not only which nestlings to feed, but when to feed themselves with preys delivered to the nests by males ( Díaz-Lora et al 2020 , 2021 ; Arco et al 2022 ). Females use a single prey per feeding event.…”

“…The hoopoe is a species with an extreme hatching asynchrony and nestling size hierarchy, in which females stay at the nests during incubation and hatching, and feed nestlings with prey delivered to the nest by the male ( Martín-Vivaldi et al 1999 ; Díaz-Lora et al 2020 ; Diaz-Lora et al 2021 ). In addition, it is worth to mention that females prefer to feed larger offspring ( Martín-Vivaldi et al 1999 ), that more than one nestling die soon after hatching in more than 70% of the nests ( Ryser et al 2016 ; Soler, Martín-Vivaldi, et al 2022 ), and that brood reduction more often occurs in poor environments ( Hildebrandt and Schaub 2018 ).…”