Defending the Weak: Parental Defense Peaks When Chick Vulnerability is Greatest in the Herring Gull (Larus argentatus)

Abstract

Successful reproduction often depends upon parents providing offspring with resources and protection. In birds, reproductive success can often be enhanced by parents engaging in antipredator behaviors, but these behaviors can be costly. Theoretically, individuals should temporally modify the intensity of nest defense behavior to balance the costs and benefits of current and future reproductive success. More specifically, nest defense should vary throughout a nesting attempt to maximize fitness of the adults. Here, we consider the relationship between nest defense behavior and chick vulnerability in the herring gull (Larus argentatus), where chicks are under high predation risk. We estimated chick vulnerability by quantifying survival probabilities at different periods of the nestling stage. Simultaneously, we quantified changes in parental aggression throughout the nesting cycle by simulating predation attempts using a human predator model. We found that chick survival probabilities were lowest (i.e., vulnerability was highest) and parental aggression in nest defense was greatest during the first 10 days after hatching. Thus, we show that parents are most defensive when chicks are most vulnerable and that adults optimize nest defense behaviors in a way that maximizes their fitness.

Plastering mud around the entrance hole affects the estimation of threat levels from nest predators in Eurasian Nuthatches

“…It has been shown that various bird species can distinguish between raptors differing in size and then perform appropriate antipredator response behaviours (Evans et al 1993;Templeton et al 2005;Courter and Ritchison 2010). However, many factors, such as habitat, nest stage, sex, nest type and predator location, may influence and cause changes in nest defence behaviour of birds (Burger 1992;Ritchison 1993;Møller et al 2016;Crisologo and Bonter 2017). For example, alarm calling rates increased with the nesting stage in Southern House Wrens (Troglodytes musculus) (Fasanella and Fernández 2009).…”

Brilliant bird brains: object recognition in Herring Gulls ( Larus argentatus smithsonianus )

“…Semirandomized trial assignments across the seven field researchers guaranteed that each gull experienced only one trial by an individual researcher, none of whom were personally involved in the prior banding or prior year's research on the Appledore gulls. Each focal individual experienced the four trials over a maximum of 5 days (mean = 2.76 days) to minimize the effects of seasonal changes in behavioral response (e.g., Crisologo and Bonter 2016). All trials were conducted between 0630 and 1935 hours and were limited to fair weather conditions.…”

Food availability affects parental anti-predator behaviour in red kites

“…In many animals, parental care involves not only provisioning food and protection from inclement weather, but also active nest defence against predators (Clutton-Brock 1991). Parents may prevent nest predation through mobbing, i.e.…”

“…The resulting departure of a predator from the nest area has a direct benefit (Curio 1978) for offspring survival (Ajie et al 2007;Andersson et al 1980;Lind and Cresswell 2005;Montgomerie and Weatherhead 1988), but driving off a predator is costly in terms of time and energy for the parents (Dugatkin and Godin 1992), and includes the risk of being injured or killed by the predator (King 1999;Mo 2017;Sordahl 1990). Hence, mobbing represents a form of parental investment, and according to life history theory, the level of this investment should depend on its cost-benefit-ratio for the parents (Clutton-Brock 1991). Thus, it is expected that mobbing behaviour varies in relation to a number of internal and external factors associated with the benefits of parental efforts (Caro 2005;Mahr et al 2015).…”

“…in young offspring; Dale et al 1996;Listoen 2000). Previous studies investigated these hypotheses by quantifying age-dependent mobbing intensity or risk-taking; however, results are equivocal, providing support for either, or both hypotheses (Crisologo et al 2017;Fernandez and Llambías 2013;Tryjanowski and Golawski 2004). The reason for this might be that the age-dependent benefits of mobbing behaviour in the two hypotheses may change with breeding conditions, while the age-dependent costs remain similar (for theoretical details, see Dale et al 1996).…”