Abstract
Several studies have found that adult birds of altricial species adjust their parental care behaviour (i.e. nest visits) in response to the current risk of predation for their offspring. However, no experimental study has so far investigated whether there are sex differences in these passive anti-predator responses during the nestling period. Differences between males and females could arise because of several factors, including (1) probability of detection, (2) confidence in parenthood, and (3) different parental care behaviour associated with each sex. To test whether these anti-predator passive responses involve sex differences, we experimentally manipulated the perceived risk of nest predation of adult Common Blackbirds (Turdus merula), a sexually dimorphic species with a relatively high extra-pair paternity level. Our results showed that nest predation significantly reduced adult visits to the nest, but not differentially between males and females, which does not support our predictions. Our findings suggest (1) that sex differences in predator-induced behaviour could depend on the type of response (active vs. passive anti-predator strategies); (2) the potential existence of a minimum threshold in detectability between males and females for these behavioural changes to occur; and (3) the contrasting and opposite effects of several factors that might impede the selection of sex differences in these types of parental care behaviour.
Highlights
Nest predation represents an important source of natural selection across taxa (Ricklefs 1969; Martin 1995) and can influence variation in life-history strategies among birds in particular
Our results showed a significant reduction in nest visits by adult Blackbirds under increased nest predation risk, fitting our prediction 1a
This agrees with previous studies on the topic (e.g. Eggers et al 2005, 2008; Massaro et al 2008; Peluc et al 2008; Zanette et al 2011; Ghalambor et al 2013; Hua et al 2014) and with the reduction in nest visits observed for female Blackbirds during the incubation stage (Ibanez-Alamo and Soler 2012)
Summary
Nest predation represents an important source of natural selection across taxa (Ricklefs 1969; Martin 1995) and can influence variation in life-history strategies among birds in particular (reviews in Martin and Briskie 2009; IbanezAlamo et al 2015). Montgomerie and Weatherhead (1988) proposed several factors that could explain active anti-predator responses by adults against threats to their offspring (i.e. nest defence): (1) confidence of parenthood, (2) renesting potential, (3) perception of risk (i.e. sexual dichromatism or body dimorphism), (4) lifehistory characteristics (i.e. mortality rate) or (5) the ability to raise offspring unaided. Some of these factors may be valid for passive anti-predator responses of adults in a context of nest predation risk (i.e. reduction of nest visits to avoid nest detection). Females are more constrained in modifying their parental care behaviour in the presence of a nest predator than are males because nestling survival depends on certain tasks frequently attended only by females (e.g. brooding; Clutton-Brock 1991), and the trade-off between costs and benefits changes according to the sex
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