Trends in annual and seasonal survival of Pink‐footed GeeseAnser brachyrhynchus

Abstract

Adult Pink‐footed Geese Anser brachyrhynchus from the Svalbard breeding population were neck‐banded and resighted in staging and wintering areas outside the breeding season 1990–1999. We estimated annual and seasonal survival using capture–recapture statistical models. Mean annual survival was 0.829, declining over the study period from 0.90 to 0.79. The annual cycle was partitioned into three periods: summer (1 April–30 September), including both spring and autumn migration, autumn (1 October–31 December), including most shooting, and winter (1 January–31 March). The parsimonious model selected to describe seasonal survival included a declining trend in summer survival, constant autumn and winter survival with lower survival in the severe winter of 1996, and an additive effect of sex on summer and winter survival. Monthly survival was highest during winter. Decreasing summer survival was the main contributor to the overall decline in annual survival, and was attributed mainly to increasing natural mortality on the breeding grounds. Mean annual survival based on the seasonal survival probabilities was 0.835 for females and 0.805 for males. The effect of sex was most pronounced during summer and remains to be explained.

Philopatry in a changing world: response of pink-footed geese Anser brachyrhynchus to the loss of a key autumn staging area due to restoration of Filsø Lake, Denmark

“…Hunting pressure may significantly influence site use among quarry species like pink-footed geese, and historically increased shooting at Filsø has pushed geese further down the flyway by accelerating southward migration (Madsen and Jepsen 1992). Based on the number of re-sighted geese, our data indicate that survival in the year following restoration (autumn 2012 to autumn 2013) was approximately 32/40 = 0.8, which is very close to the expected value of 0.797 estimated from annual survival in the 1990s and the retention of neck collars (Clausen et al 2015;Madsen et al 2002). Although an exhaustive analysis of survival is not possible based on currently available data, this indicates that mortality of former philopatric geese was not immediately affected by the loss of staging site.…”

“…In 2012, 2013 and 2014, the proportion of these 78 birds observed anywhere in Denmark fell to 51, 41 and 28 %, respectively. Although this development translates to steadily declining sample sizes, it is also exactly what would be expected from the annual mortality rate of 17.1 % (Madsen et al 2002) and annual neck collar loss of 3.2 % (Clausen et al 2015) characteristic of the population. This is strong evidence that very few (if any) birds were entirely missed, due to the comprehensive and consistent re-sighting effort and systematic re-sighting campaigns (Madsen et al 2002).…”

“…Although this development translates to steadily declining sample sizes, it is also exactly what would be expected from the annual mortality rate of 17.1 % (Madsen et al 2002) and annual neck collar loss of 3.2 % (Clausen et al 2015) characteristic of the population. This is strong evidence that very few (if any) birds were entirely missed, due to the comprehensive and consistent re-sighting effort and systematic re-sighting campaigns (Madsen et al 2002). During the pre-restoration period (2008)(2009)(2010)(2011), the annual return rate of site-faithful geese to Filsø averaged 88.3 %, which after the restoration (2013-2014) declined to 9.3 % (N = 6, t = 8.950, P = 0.006; Fig.…”

“…For birds fulfilling this criterion, we analysed annual site use (presence/absence: whether an individual was or was not observed in any given staging area) in September-October (time of peak migration in Denmark) for three periods corresponding to pre-restoration (2008-2011), during restoration (2012) and post-restoration (2013-2014). To guarantee a comprehensive and consistent re-sighting effort, systematic re-sighting campaigns have been carried out during autumn along the entire flyway of this population since 1990, ensuring several re-sightings of live birds during autumn migration (Madsen et al 2002). In addition, the systematic sightings were supplemented by observations reported online by voluntary observers via the homepage www.geese.org.…”

“…Pink-footed geese have been subject to a long-term ringing scheme that began in the late 1980s, and since 1990 geese have been fitted with individually recognizable neck collars enabling tracking of individual birds to study migration, dispersal and demographics (Madsen 2001;Madsen et al 2002). Birds have been caught by either cannon-net captures in Denmark during the spring or roundups of moulting family groups on Svalbard during the summer, and the percentage of ringed birds in the population has generally been around 0.5-1.0 % (Ganter and Madsen 2001).…”