Abstract
Theoretical models predict that parents feeding offspring should partially compensate for the reduced care of their partner. However, for incubating birds, the level of compensation may depend on how reduced care changes the risk of entire brood failure, for example due to clutch predation, and on individual variation in the timing of depletion of energy stores. Although biparental incubation dominates in non-passerines, short-term manipulations of care during incubation are scarce. Here, we describe the response of 25 semipalmated sandpipers (Calidris pusilla) to an unexpected ~12-hour absence (experimental removal) of their partner in the middle of the 21-day incubation period. During the period when the removed partner would have taken over to start its regular ~12-hour incubation bout, parents compensated partially for the absence of their partner’s care (mean: 59%). However, individuals varied in their response from no to full compensation, independent of parental sex. In contrast to incubation in undisturbed nests or by uniparental species, nest attendance of compensating parents tended to be higher during the warmer part of the day. Whereas compensation was unrelated to before-experimental share of incubation, parents that left the nest from a further distance upon human approach (more aware of or more ‘responsive’ to their environment) compensated more. The quality of incubation in the after-experimental period, i.e. after return of the partner, was lower than usual, but improved quickly over time. In seven nests where the removed parent never returned, the widowed partner attended the nest for 0-10 days (median: 4), which suggests that widowed semipalmated sandpipers can adjust their incubation behavior to that observed in uniparental incubators. To conclude, our results indicate that biparental incubators are willing to tolerate a missed or irregular incubation bout of their partner and we speculate that all individuals would compensate fully, but that some fail because they deplete their energy stores, while others may be less responsive to or initially even unaware of the absence of their partner.
Highlights
Biparental care can be seen as a complex social behavior where females and males cooperate in the rearing of their offspring
Nest attendance Treated period total time on the nest) in the treated period was on average 0.38 (95%credible intervals (CI): 0.27–0.49) lower than in the control period (Figure 3B; Table S1 in Bulla, 2019). This translates to a 59% (95%CI: 49–70%) compensation for the absence of the partner
Our results indicate that semipalmated sandpipers on average partially compensated for the temporal absence of care from their partner, which seems in line with the general prediction of partial compensation from established parental care models (Houston and Davies, 1985; McNamara et al, 1999, 2003)
Summary
Biparental care can be seen as a complex social behavior where females and males cooperate in the rearing of their offspring. Established theoretical models predict that parents should partially compensate for a reduction in their partner’s care when an increase in parental care increases breeding success, but with diminishing returns (Houston and Davies, 1985; McNamara et al, 1999, 2003; reviewed by Lessells, 2012) These models have been mainly developed for and experimentally tested in passerine birds feeding their nestlings. Partial compensation is unlikely when breeding attempts fail due to a small decrease in parental care (Jones et al, 2002), when parents lack information about the brood need (including each other’s effort) or lack the capacity to compensate (Johnstone and Hinde, 2006) These circumstances might be typical for biparental incubation of eggs in birds. The latter two, i.e., insufficient information about the brood need and lacking the capacity to compensate (Johnstone and Hinde, 2006), likely occur in species where the off-duty parent leaves the nest for several hours (e.g., Grant, 1982; Blanken and Nol, 1998; Wiebe, 2008) or even days (e.g., Johnstone and Davis, 1990; Weimerskirch, 1995; Gauthier-Clerc et al, 2001) and stays at distances from the nest that preclude instantaneous communication with the incubating partner, i.e., parents can communicate only when exchanging their incubation duties
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