Variation in parental care in the spectacled tyrant Hymenops perspicillatus is associated with increased nest predation in grassland fragments

Abstract

Predation risk on birds is often an important source of natural selection that shapes parental care and may promote behavioral changes. Parents can often estimate certain risks and adjust their behavior to reduce the likelihood of nest predation. The fragmentation of habitats is one of the main consequences of loss of habitats, and in general, for birds breeding in smaller patches, their daily nest-survival rate is lower due to increased nest predation. Since nest survival is an estimate of predation risk in the environment, we evaluated the daily survival rate (DSR) for nests of spectacled tyrants (Hymenops perspicillatus) and parental care behavior on fragmented and unfragmented grasslands. We conducted nest searching and monitoring during the 2012-2013 breeding season in small patches and in a continuous patch of grassland. In addition, parental activity was recorded using video monitoring. We found a lower DSR for the spectacled tyrant in fragmented grasslands, associated with increased nest predation risk; females showed a variation in parental care. This variation was evidenced by larger incubation bouts and lower visitation rate during the incubation period, and by a lower food delivery rate to nestlings, compensated by larger prey sizes. The results show that fragmentation not only reduces the fitness of individuals and impacts adversely on population, but individuals are also subjected to a strong selection pressure, and their reproductive success may depend to some extent on the ability of parents to estimate at least certain predation risk and adjust their behavior in this regard.

Flexible responses to stage‐specific offspring threats

“…Our data show that chickadees did not alter reproductive strategy later in the breeding attempt, consistent with the idea that response to house wren threat is flexible and stage-specific. While other studies show that presence of a general offspring predator (i.e., a predator that is also a threat to nestlings) may influence feeding rate (Chalfoun & Martin, 2010;Fontaine & Martin, 2006;Pretelli et al, 2016;Sofaer et al, 2012;Yoon et al, 2016;Zanette et al, 2011), we found no such differences. We found instead that variation in number of both total feeding trips and per nestling feeding trips was mostly explained by brood size: Larger broods had more total trips but fewer trips per nestling.…”

“…Threats from predation can result in costly alterations in parental behavior throughout nesting (i.e., both egg and nestling stages) because general offspring predators are often relevant throughout the entire breeding attempt (e.g., Fontaine & Martin, ; Zanette, White, Allen, & Clinchy, ). In the presence of a threat, parents can alter behavior that results in reduced clutch size (Doligez & Clobert, ; Eggers, Griesser, Nystrand, & Ekman, ; Hua, Sieving, Fletcher, & Wright, ; Zanette et al, ), reduced clutch mass (Fontaine & Martin, ), changes in incubation behavior (Conway & Martin, ; Ferretti, Llambías, & Martin, ; Ibáñez‐Álamo & Soler, ; Massaro, Starling‐Windhof, Briskie, & Martin, ), and reduced nestling provisioning (Chalfoun & Martin, ; Dudeck, Clinchy, Allen, & Zanette, ; Fontaine & Martin, ; Pretelli, Isacch, & Cardoni, ; Sofaer, Sillett, Peluc, Morrison, & Ghalambor, ; Yoon, Kim, Joo, & Park, ; Zanette et al, ). Increased time off the nest during incubation results in eggs with decreased embryo mass, reduced residual yolk, and reduced growth efficiency (Olson, Vleck, & Vleck, ) and decreased nestling provisioning is associated with slower nestling growth and poorer quality nestlings (Scheuerlein & Gwinner, ; Thomson et al, ; Zanette et al, ).…”

“…Alternatively, if Carolina chickadees show an integrated response, we expect to see that parents in the presence of house wrens will alter their reproductive strategy in both the egg and the nestling stage, even though house wrens are primarily a threat only during the former (Figure b). Specifically, we predict that in addition to egg stage changes, parents will also decrease nestling provisioning (Chalfoun & Martin, ; Dudeck et al, ; Fontaine & Martin, ; Pretelli et al, ; Sofaer et al, ; Yoon et al, ; Zanette et al, ) and decrease nestling stage length which may reduce time at risk in the nest (Hua et al, ; Remeŝ & Martin, ; Yoon et al, ). We discriminate between the predictions of a dissociable response versus the predictions of an integrated response by measuring and comparing life history traits of free‐living chickadees naturally nesting in boxes that are near nesting house wrens to chickadees nesting in boxes that are not.…”

“…Specifically, we predict that in addition to egg stage changes, parents will also decrease nestling provisioning (Chalfoun & Martin, 2010;Dudeck et al, 2018;Fontaine & Martin, 2006;Pretelli et al, 2016;Sofaer et al, 2012;Yoon et al, 2016;Zanette et al, 2011) and decrease nestling stage length which may reduce time at risk in the nest (Hua et al, 2014;Remeŝ & Martin, 2002;Yoon et al, 2016).…”

Evolution of parental activity at the nest is shaped by the risk of nest predation and ambient temperature across bird species

“…; Pretelli et al. ). In addition, experimental manipulation of perceived predation risk resulted in changes in the activity at the nest in several species (Kovařík and Pavel ; Ibáñez‐Álamo and Soler ; Basso and Richner ).…”