Intruders in Nests of the Spotless Starling: Prospecting for Public Information or for Immediate Nesting Resources?

Abstract

The prospective behaviour for nests by conspecific intruders may be a strategy to gather public information for future reproduction or to secure resources for immediate reproduction. Although the relationship between the sex, age and breeding experience of intruders and the sex and age of residents may be crucial for understanding the significance of nest‐prospecting behaviour, a precise determination of these traits has rarely been addressed in field studies. In a free‐ranging population of spotless starlings ( Sturnus unicolor), inexperienced birds were the predominant intruders. The ratio of male‐to‐female intruders was higher among birds without previous breeding experience, although our results did not allow us to determine whether more inexperienced males or females intruded nests. The average annual rate of intrusion of either sex was strongly correlated with the number of fledglings produced in the study colony the previous year, which seems to indicate that the inexperienced intruders were, in general, yearlings. The proportion of the sexes among the intruders in each study year was correlated with the average age of male owners but not with the age of female owners. This result suggests that the presence of intruding males in the nests was affected by an increased opportunity to find vacancies in nesting territories as resident males became older. This finding supports the hypothesis that, in most cases, birds visited nests to obtain personal information about nesting resources. However, the intrusion rates were higher when there were nestlings than during the incubation period, which suggests that collecting public information was also involved in the intruding behaviour. Both sexes regularly attacked intruders, which implies that the intruders inflicted some kind of cost on the owners. Female floaters were more frequently chased, probably because they regularly lay parasitically in conspecific nests.

Age of First Breeding Interacts with Pre- and Post-Recruitment Experience in Shaping Breeding Phenology in a Long-Lived Gull

“…During prospecting, individuals are believed to gather knowledge about potential breeding partners, territories, foraging sites and food supply, which may allow for a better integration into the breeding population afterwards. In support of this, several studies showed direct or indirect fitness benefits from prospecting behaviour prior to the first breeding attempt, e.g., [ 28 - 33 ], also in relation to arrival timing. For instance, in Common tern ( Sterna hirundo ), former prospectors arrived significantly earlier in the breeding colony during their reproductive life [ 29 ].…”

Density dependence of clutch size and offspring sex ratio in starling colonies

“…Female starlings overproduced daughters when breeding in high‐density (HD) plots and this effect was consistent during the five years of the experiment. The experimental aggregation of nest boxes may have increased the competition for breeding resources and the number of agonistic interactions among neighbouring females and against intruders (Veiga et al 2012, Rubalcaba et al 2017b). This increased competition was previously found to reduce reproductive success of female starlings (Rubalcaba et al 2017a, Fuentes et al 2019), probably because females breeding in high‐density plots invested more time guarding or defending their nests against intruders, which reduced their investment in parental care activities (Veiga and Polo 2008, Polo et al 2010, 2015, Veiga et al 2012).…”

“…The experimental aggregation of nest boxes may have increased the competition for breeding resources and the number of agonistic interactions among neighbouring females and against intruders (Veiga et al 2012, Rubalcaba et al 2017b). This increased competition was previously found to reduce reproductive success of female starlings (Rubalcaba et al 2017a, Fuentes et al 2019), probably because females breeding in high‐density plots invested more time guarding or defending their nests against intruders, which reduced their investment in parental care activities (Veiga and Polo 2008, Polo et al 2010, 2015, Veiga et al 2012). Under these conditions, parents may benefit from overproducing daughters because 1) the lifetime reproductive success of daughters depends less on their condition at fledging than that of their brothers (Rubalcaba and Polo 2018); and 2) because daughters disperse further away from their natal territory (Rubalcaba et al 2017a), which may reduce future local competition for breeding resources.…”

The Unknown Life of Floaters: The Hidden Face of Sexual Selection

“…In females also, the desperate attempts by floaters to attain breeding opportunities may have contributed to the observed propensi-ties for prospecting by females (Veiga et al, 2013) and for female-female aggression and the signalling of female dominance towards other females (Stutchbury and Robertson, 1987;Moreno et al, 2014). Female floaters may frequently be chased away by territory owners to preclude IBP tactics (Veiga et al, 2012) and this may lead to increased androgen levels in females in high density situations with the presence of more floaters (Pilz and Smith, 2004). The need to avoid such aggression may have selected for delayed plumage maturation in females of some species (Coady and Dawson, 2013).…”