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- 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
More Like this
-
more » « less
Abstract -
null (Ed.)As global land surfaces are being converted to urban areas at an alarming rate, understanding how individuals respond to urbanization is a key focus for behavioral ecology. As a critical component of avian parental care, incubating adults face a tradeoff between maintaining an optimal thermal environment for the developing embryos while meeting their own energetic demands. Urban habitats are biotically and abiotically different from their rural counterparts, i.e ., in food availability, predator compositions, and the thermal environment. Therefore, urban birds may face different incubation challenges than their natural counterparts. We measured incubation behavior of rural and urban house wrens, Troglodytes aedon , with temperature loggers throughout the 12-day period. We found that urban females had more incubation bouts of shorter duration and spent less total time incubating per day than rural females. Results could provide evidence of behavioral shifts of wrens in cities, which have implications for the evolution of parental care. Our findings contribute to our understanding of the behavioral traits needed for city life and possible environmental pressures driving urban adaptations.more » « less
-
more » « less
Abstract The strategies by which animals allocate reproductive effort across their lifetimes vary, and the causes of variation in those strategies are actively debated. In birds, most research has focused heavily on variation in clutch size and fecundity, but incubation behaviour and other functionally related traits have received less attention. Variation in incubation period duration is notable because time‐dependent sources of clutch mortality should impose strong directional selection to minimize the incubation period. However, life‐history theory predicts multiple mechanisms by which inter‐ and intraspecific variation in incubation behaviours may be adaptive.
We conducted one of the first studies of intraspecific latitudinal variation in avian incubation behaviours across a large portion of a single species’ range. We placed motion‐activated nest cameras inside burrowing owl nests at five study sites to quantify variation in daily nest attentiveness, cumulative nest attendance and incubation period duration. We tested predictions of two alterative hypotheses that have been proposed to explain variation in incubation periods: the
parental risk tolerance hypothesis and theneonate quality hypothesis .Daily nest attentiveness, cumulative nest attendance and incubation period duration in burrowing owls were all positively correlated with latitude. Burrowing owls reduced their daily nest attentiveness at low latitudes and on days when the average nest temperature was within the range that is optimal for embryo development. Further, longer incubation periods were most strongly associated with greater cumulative nest attendance instead of reduced daily nest attentiveness.
These results support predictions of the
neonate quality hypothesis: longer incubation periods result from stronger selection on neonate quality rather than selection to reduce reproductive effort in response to low extrinsic mortality risk. However, some owls facultatively reduced their daily nest attentiveness, and this result supports the general hypothesis that incubation decisions reflect a trade‐off between reproduction and self‐maintenance, and that the optimal solution to that trade‐off varies systematically in response to latitudinal gradients in adult mortality.A free
Plain Language Summary can be found within the Supporting Information of this article. -
The Arctic Coastal Plain is one of the most important avian breeding grounds in the world; however, many species are in decline. Arctic‐breeding birds contend with short breeding seasons, harsh climatic conditions, and now, rapidly changing, variable, and unpredictable environmental conditions caused by climate change. Additionally, those breeding in industrial areas may be impacted by human activities. It is difficult to separate the impacts of industrial development and climate change; however, long‐term datasets can help show patterns over time. We evaluated factors influencing reproductive parameters of breeding birds at Prudhoe Bay, Alaska, 2003–2019, by monitoring 1265 shorebird nests, 378 passerine nests, and 231 waterfowl nests. We found that nest survival decreased significantly nearer high‐use infrastructure for all guilds. Temporally, passerine nest survival declined across the 17 years of the study, while there was no significant evidence of change in their nest density. Shorebird nest survival did not vary significantly across years, nor did nest density. Waterfowl nest density increased over the course of the study, but we could not estimate nest survival in all years. Egg predator populations varied across time; numbers of gulls and ravens increased in the oilfields 2003–2019, while Arctic fox decreased, and jaeger numbers did not vary significantly. Long‐term datasets are rare in the Arctic, but they are crucial for understanding impacts to breeding birds from both climate change and increasing anthropogenic activities. We show that nest survival was lower for birds nesting closer to high‐use infrastructure in Arctic Alaska, which was not detected in earlier, shorter‐term studies. Additionally, we show that Lapland longspur nest survival decreased across time, in concert with continent‐wide declines in many passerine species. The urgency to understand these relationships cannot be expressed strongly enough, given change is continuing to happen and the potential impacts are large.more » « less
-
Romanach, Stephanie S (Ed.)more » « less
Atlantic ghost crabs (
Ocypode quadrata ) are predators of beach-nesting shorebird nests and chicks on the United States’ Atlantic and Gulf coasts. Ghost crabs may also disturb birds, altering foraging, habitat use, or nest and brood attendance patterns. Shorebird conservation strategies often involve predator and disturbance management to improve reproductive success, but efforts rarely target ghost crabs. Despite the threat to shorebird reproductive success, ghost crabs are a poorly understood part of the beach ecosystem and additional knowledge about ghost crab habitat selection is needed to inform shorebird conservation. We monitored ghost crab activity, defined as burrow abundance, throughout the shorebird breeding season on Metompkin Island, Virginia, an important breeding site for piping plovers (Charadrius melodus ) and American oystercatchers (Haematopus palliatus ). We counted burrows at shorebird nests and random locations throughout the breeding season and investigated whether ghost crab activity was greater at nest sites relative to random locations without shorebird nests. While we observed burrows at all nest sites (n = 63 nests), we found that burrow counts were lower at piping plover nests with shell cover, relative to random locations with no shell cover. Ghost crabs may avoid piping plover nest sites due to anti-predator behaviors from incubating adults or differences in microhabitat characteristics selected by piping plovers. We also investigated the effects of habitat type, date, and air temperature on the abundance of ghost crab burrows. We found that while crab burrows were present across the barrier island landscape, there were more burrows in sandy, undisturbed habitats behind the dunes, relative to wave-disturbed beach. Additionally, ghost crab activity increased later in the shorebird breeding season. Understanding when and where ghost crabs are most likely to be active in the landscape can aid decision-making to benefit imperiled shorebird populations.
