Experimental Evidence that Sexual Displays are Costly for Nest Survival

Abstract

Nest predation is one of the most significant limitations for successful breeding of tropical passerines. Thus, parental strategies may include choosing appropriate nest sites and behaving in ways that minimize predation. Habitat characteristics that may influence nest success include degree of nest concealment, proximity to habitat edge, plant architecture as well as several others cited in the literature. However, few studies have examined display behavior as a factor that could also influence nest survival. We experimentally tested whether sexual motor displays served as a cue for visually oriented predators to locate artificial nests in a population of blue‐black grassquits Volatinia jacarina, a Neotropical passerine that exhibits a complex sexual display and is subjected to elevated rates of nest predation. We also evaluated the effect of nest substrate on survival. Predation rate was higher for nests within territories of displaying males relative to areas without displaying males and for nests placed in shrubs relative to grasses. Predation increased sharply in the third experimental replicate, at the end of the breeding season, which suggests that predators may develop a search image for nests or may become more abundant during specific periods of the season. Avian predators appear to be the most important nest predators. Results suggest that there may be a trade‐off between the increase in fitness derived from sexual displays of males to attract potential mates and the decrease owing to predation of active nests within their territories.

Conspicuous sexual signals in a socially monogamous passerine: the case of neotropical Blue-black Grassquits

“…To test this hypothesis, we used artificial nests baited with quail eggs introduced into displaying Blue-black Grassquit male territories and compared their rate of predation with similar nests placed in comparable vegetation and heights, but which lacked the presence of a displaying male. We found that predation rate was significantly higher when nests were associated with displaying males (Dias et al 2010). The results of this experiment bring into sharp focus the tradeoffs associated not only with the display itself but also relative to the female dilemma when choosing a mate.…”

“…One recent experimental field study produced suggestive evidence that the leaping displays of male Blue-black Grassquits are costly in terms of nest survival (Dias et al 2010). This study was developed due to suggestions in the literature that several parental and offspring behaviors may attract predators to the nest, including begging by chicks and feeding trips by parents (Skutch 1949;Haskell 1994;Leech and Leonard 1997;Martin et al 2000).…”

Dangerous love? Predation risk does not affect female mate choice in blue‐black grassquits

“…Our final scenario predicted that females would select more conspicuous male stimuli only in situations of low risk, and under high predation risk, they would choose male stimuli at random or even prefer more muted stimuli. This latter outcome assumed that association with vigorously displaying males might impose a great survival cost on females or their potential offspring (Dias et al, ; Marzal et al, ). Our results confirmed the first predicted scenario, given that females were non‐responsive to male song stimuli, whether at low or high rates, across all experimental treatments.…”

“…Males maintain their sexual displays even after establishing a socially monogamous breeding pair (Macedo et al, ), probably to attract neighboring females to obtain extrapair copulations (Carvalho, Macedo, & Graves, ; Manica et al, ). Males perform these conspicuous displays despite having an active nest in their territories, and this has been shown to increase predation risk for nests (Dias, Castilho, & Macedo, ).…”

“…The third outcome assumes that females do not benefit from choosing conspicuous males in high predation risk environments. The greater reproductive costs endured by females with the increased predation risk to themselves (Marzal et al, ), and their offspring (Dias et al, ) cancel the benefits of pairing with a conspicuous male. In this scenario, females should favor conspicuous males during the no‐risk control treatment (assuming that male conspicuousness is sexually selected by females in optimal conditions—Godin & Briggs, ) and in contrast, should either be non‐responsive to male display conspicuousness or show a greater response to less conspicuous males when predation risk is high (simulation of adult and/or nest predators).…”