The Skutch (1949) Hypothesis that nest predation risk constrains parental nest activity has important implications for the evolution of parental care strategies, but the required conditions for the hypothesis to operate have been questioned. We found the necessary conditions existed in a montane tropical bird community where 95.4% of predation events (n = 456) occurred during daylight hours and almost all predators (n = 224) were visually oriented. Moreover, incubation strategies for 21 passerine species were explained by nest predation rates as proposed by the Skutch Hypothesis. Hourly rates of visits to the nest were lower among species with higher nest predation rates, and achieved in part by longer on- and off-bouts. Incubation attentiveness (percent of time incubating) does not necessarily affect parental nest activity and was not related to nest predation rates. Nest predation rates were greater in enclosed- than open-nesting species, counter to long-standing views. Moreover, nest predation was usually higher in the nestling period when parents were more actively visiting nests than during incubation for enclosed- but not open-nesting species. This increase in nest predation in the nestling period for enclosed-nesting species might indicate proximate predation responses to parental nest activity that underlie the evolutionary patterns. Adult mortality also can exert selection on evolved strategies. Following life history theory, annual adult mortality probability explained residual variation in incubation behaviors, while accounting for nest predation, with longer-lived species exhibiting lower nest activity and attentiveness. Ultimately, the conditions for the Skutch Hypothesis were clear and evolved behaviors suggest an important influence of natural selection by nest predation in this montane tropical bird community. At the same time, different patterns of nest predation between open- and enclosed-nesting species emphasize a need for further research into how parental nest activity interacts with nest type to affect predator detection of nests.
Nest predation influences population dynamics and is thought to exert strong selection on the evolution of avian life history. Because parental behaviors can attract the attention of nest predators, incubating birds are predicted to decrease conspicuous behaviors at the nest-site and increase incubation constancy when risks of nest predation are high. We examined whether snowy plovers Charadrius nivosus responded to predator-specific risks of nest predation, using the number of off bouts and daily nest attendance (proportion of time spent incubating) as responses. We quantified risks using predator-specific hazard rates of nest mortality, which varied daily and were based on habitat characteristics at each nest. We assessed the influence of predator-specific risks of nest mortality on incubation behaviors using an individual-centering approach, allowing us to explain variation in incubation behaviors within- and among-breeding pairs. We found increased number of off bouts and nest attendance within-breeding pairs in response to increasing risks of nest predation by foxes (Vulpes spp.) and gulls (Larus spp.), but not coyotes (Canis latrans) and common ravens (Corvus corax). Among breeding pairs across habitats, we found increased nest attendance in response to higher risks of nest predation by foxes, but not coyotes, gulls, or ravens. Breeding pairs differed in the amount of behavioral plasticity they exhibited in response to risks of nest predation. Our results suggest that risks of nest predation differentially influence behavioral responses of snowy plovers depending on the predator species, and the amount of behavioral plasticity may depend on the characteristics of breeding adults.
more » « less- NSF-PAR ID:
- 10374415
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Behavioral Ecology
- Volume:
- 33
- Issue:
- 5
- ISSN:
- 1045-2249
- Format(s):
- Medium: X Size: p. 937-945
- Size(s):
- p. 937-945
- Sponsoring Org:
- National Science Foundation
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