The demographic drivers of local population dynamics in two rare migratory birds

Abstract

The exchange of individuals among populations can have strong effects on the dynamics and persistence of a given population. Yet, estimation of immigration rates remains one of the greatest challenges for animal demographers. Little empirical knowledge exists about the effects of immigration on population dynamics. New integrated population models fitted using Bayesian methods enable simultaneous estimation of fecundity, survival and immigration, as well as the growth rate of a population of interest. We applied this novel analytical framework to the demography of two populations of long-distance migratory birds, hoopoe Upupa epops and wryneck Jynx torquilla, in a study area in south-western Switzerland. During 2002-2010, the hoopoe population increased annually by 11%, while the wryneck population remained fairly stable. Apparent juvenile and adult survival probability was nearly identical in both species, but fecundity and immigration were slightly higher in the hoopoe. Hoopoe population growth rate was strongly correlated with juvenile survival, fecundity and immigration, while that of wrynecks strongly correlated only with immigration. This indicates that demographic components impacting the arrival of new individuals into the populations were more important for their dynamics than demographic components affecting the loss of individuals. The finding that immigration plays a crucial role in the population growth rates of these two rare species emphasizes the need for a broad rather than local perspective for population studies, and the development of wide-scale conservation actions.

Relative contribution of local demography and immigration in the recovery of a geographically-isolated population of the endangered Egyptian vulture

“…However, the paucity of CR surveys in Pyrenees and Iberian Peninsula implied a low detection of long-distance dispersers whereas some birds could disperse among populations, as showed by the increasing proportion of non-ringed birds seen at restaurants and the recent identification of three Spanish birds recruited in south-eastern France (authors' unpublished data). Our study highlights the impact of those few birds dispersing among populations and our findings participate to the growing evidence for the crucial role played by immigration in shaping bird population dynamics (Altwegg et al, 2014;Brown and Collopy, 2012;Schaub et al, 2012;Tempel et al, 2014), especially in long-lived raptors (Hernández-Matías et al, 2013;Schaub et al, 2010;Tauler et al, 2015).…”

“…Usually, survival and reproduction are estimated from local monitoring assuming that the focal population is closed or that emigration equilibrates immigration. However, evidence is increasing that immigration plays a crucial role in restoring populations which are intrinsically declining despite an apparent stability (Brown and Collopy, 2012;Schaub et al, 2010Schaub et al, , 2012Tempel et al, 2014). Thus, the spatial scale at which conservation actions are evaluated should take these immigration and emigration fluxes into account.…”

Territory Occupancy and Parental Quality as Proxies for Spatial Prioritization of Conservation Areas

“…We determined sex and age (two classes: one year old and older, recognizable from moult patterns of wing feathers; Mosimann-Kampe unpublished data), and measured the lengths of bill, crest, the fifth primary feather (P5), the first tail feather (R1) and tarsus, as well as body mass. All captured individuals as well as all nestlings were ringed [22].…”

Estimating immigration using a Bayesian integrated population model: choice of parametrization and priors

“…Immigration is an important demographic process that has long been a neglected component of population modelling, even though it may have a strong impact on population dynamics (Ward 2005;Lampila et al 2006;Grøtan et al 2009;Schaub et al 2010Schaub et al , 2012Schaub et al , 2013Brown and Collopy 2013). An assessment of the amount of immigration into a population can help identify whether a local population is a sink (Pulliam 1988;Peery et al 2006) and therefore how it might be managed.…”

“…Unlike other demographic parameters, there is some choice as to how immigration is parametrized. It might be convenient to specify immigration as a rate, analogous to the definition of a survival probability (Cooch et al 2001;Abadi et al 2010b;Schaub et al 2010Schaub et al , 2012. However, unlike in the case of survival, there is some arbitrariness in the choice of the denominator.…”