Effects of Population Density on Survival in Merlins

Abstract

Accurate estimation of survival probabilities is an important component of population demographics, and it permits a test of the life-history prediction that densities influence population dynamics via suppression of survival rates. As part of a long-term study of urban-nesting Merlins (Falco columbarius), we estimated survival rates and tested for the effects of density dependence based on capture histories from 1,354 individuals (43 males and 110 females caught for the first time as adult breeding birds, and 597 males and 604 females caught for the first time as locally produced nestlings). Overall capture probabilities were 0.55 ± SD of 0.039 per year for adults, 0.10 ± 0.075 per year for juvenile males, and 0.58 ± 0.23 per year for juvenile females. Mean survival rate of adults was 0.62 ± 0.11 per year and did not differ significantly between males and females. Overall juvenile survival rates were 0.23 ± 0.032 for males and 0.055 ± 0.012 for females. Band returns suggest that the discrepancy in survival rates between juvenile males and females resulted from higher natal dispersal of females rather than from lower survival. Survival of adults (but not juveniles) was negatively density dependent, suggesting that density-dependent declines in survival exerted a regulatory effect on population size.

Declining survival rates in a reintroduced population of the Mauritius kestrel: evidence for non‐linear density dependence and environmental stochasticity

“…The recognition of different survival probabilities among adult and juvenile Mauritius kestrels agrees with many results found in other long-term population studies Frederiksen & Bregnballe 2000;Lieske et al 2000;Larter & Nagy 2001). The survival probabilities exhibited by juvenile Mauritius kestrels over the course of the population's development (Fig.…”

“…The recognition of different survival probabilities among adult and juvenile Mauritius kestrels agrees with many results found in other long‐term population studies (Gaillard et al . 1998; Frederiksen & Bregnballe 2000; Lieske et al . 2000; Larter & Nagy 2001).…”

“…Density‐dependent survival has been identified in long‐term studies of stable and fluctuating populations for a wide range of species (Tinbergen, Vanbalen & Vaneck 1985; Francis et al . 1992; Lieske et al . 2000; Larter & Nagy 2001).…”

Variation in selection pressure acting on body size by age and sex in a reverse sexual size dimorphic raptor

“…From 1985 to 1995, as population density increased to a stable plateau, there was a density‐dependent decrease in survivorship among adult Merlins (Lieske et al . ). The largest individuals in the population (who are likely to choose a proportionately large mate) may have been particularly constrained during this period by the energetic requirements of maintaining a large body while encountering increased competition for territories and prey, leading to decreased survivorship.…”

Experimental evidence for density‐dependent reproduction in a cooperatively breeding passerine

“…Density dependence is a process that explains why populations normally fluctuate between certain numbers (Murdoch 1994, Saether et al 2002. Although many studies find negative relationships between density and reproduction (Kluyver 1951, Perrins 1965, Alatalo and Lundberg 1984, Arcese et al 1992 or survival (Tinbergen et al 1985, Francis et al 1992, Lieske et al 2000, this is not the case in all studies (van Balen and Potting 1990, Nur and Sydeman 1999, Loison et al 2002, Festa-Bianchet et al 2003. Furthermore, even within species there can be considerable variation in the occurrence of density dependence (Both 2000).…”