Habitat‐specific differences in adult survival rates and its links to parental workload and on‐nest predation

Abstract

Summary1. Adult survival rates strongly affect population growth, but few studies have quantified if and why adult survival differs between breeding habitats. We investigated potential causes of habitatspecific adult survival rates for male and female northern wheatears (Oenanthe oenanthe L.) breeding in Swedish farmland. 2. We used multistate mark-recapture models based on 1263 breeding records between 1993 and 2007 to estimate survival rates based on habitat-type (SHORT vs. TALL ground vegetation) and breeding-success state parameters. We also used breeding-season observations from 2002 to 2007 and an experimental manipulation of ground vegetation height to identify factors influencing adult mortality. 3. Females had lower annual survival than males (0AE42 ± 0AE02 vs. 0AE50 ± 0AE02); this difference largely resulted from low female survival in TALL habitats because of higher nest-predation risk and the large proportion of adult females being killed on the nest (>20%) during nest predation events. 4. Among successful breeders, both sexes displayed similar survival rates, but survival was lower for breeders in TALL as compared to SHORT habitats (0AE43 ± 0AE03 vs. 0AE51 ± 0AE02). Experimental manipulation of ground vegetation height, controlling for individual and territory quality (n = 132), suggested the cost of rearing young to be higher in TALL habitats (survival of successful breeders in TALL vs. SHORT; 0AE43 ± 0AE11 vs. 0AE57 ± 0AE05). 5. Detailed observations of food provisioning behaviour during chick rearing revealed a habitatrelated difference in parental workload corresponding to the observed habitat differences in adult survival for successful breeders. Adults breeding in TALL habitats were forced to forage further from the nest relative to SHORT-habitat breeders (mean ± SE; 69 ± 10 vs. 21 ± 2 m), which increased the estimated daily workload for adults in TALL vs. SHORT habitats by c. 20%. 6. On-nest predation and parental workload during chick rearing combine to largely explain habitat-specific adult survival rates. The results have implications for our understanding of adult sex ratios, causes of source-sink demography and habitat-specific growth rates. Furthermore, it suggests SHORT field margins and other residual habitat elements to be important for the conservation of farmland passerines breeding in cropland plains.

Conditions at autumn stopover sites affect survival of a migratory passerine

“…This pattern is different from that found in the majority of other bird species, where annual survival is typically higher for males than for females (e.g. Stokke et al 2005;Low et al 2010). Interestingly, however, Thaxter et al (2006) found opposite patterns (higher and lower male survival compared to the females) in two populations of British Reed Warblers, suggesting that sexbased survival and/or emigration may be site-specific in the species.…”

Costs of Reproduction in Breeding Female Mallards: Predation Risk during Incubation Drives Annual Mortality

“…During egg-laying, female birds gain mass that is not compensated for by increased muscle development, and this may impair escape flight and put gravid females at greater risk (Lee et al 1996). Incubation and brood care are thought to place parent birds at greater predation risk (Vehrencamp 1978, Hartke et al 2006, Low et al 2010), but mortality of parents is much harder to document than mortality of sedentary eggs or prefledged young, and so these risks have not been well documented. Determining event-specific mortality among breeding adults generally requires techniques such as telemetry or video surveillance (Hartke et al 2006, Reidy et al 2009), which often precludes large samples and raises concerns that the methodologies themselves may affect mortality risks (Richardson et al 2009, Barron et al 2010.…”

Effects of variation in breeding habitat on Ring OuzelTurdus torquatusproductivity and chick condition

“…For example, Low et al (2010) found that adult workload is higher in poorer quality habitat for Northern Wheatear Oenanthe oenanthe: the rate of provisioning visits to the nest was the same, but the distances flown per visit were much higher. This variation in adult energy expenditure of up to 30% resulted in a decline in adult survival with decreasing habitat quality.…”

“…Within a breeding season, the costs of reproduction can vary (spatially or temporally) between pairs due to heterogeneous environmental variables, such as habitat and/or food availability. Pairs can pass on high costs of reproduction to the number of chicks fledged (Martinez 2012), to juvenile survival (Piper et al 2012), to adult survival (Low et al 2010) or to a combination of these traits (Lambrechts et al 2004, Kerbiriou & Julliard 2007, Santangeli et al 2012, Seward et al 2013. Variation in habitat can therefore potentially influence any demographic parameter.…”