Management of a Dutch resident barnacle goose Branta leucopsis population: How can results from counts, ringing and hunting bag statistics be reconciled?

The resident Dutch Northern Delta barnacle geese Branta leucopsis population expanded steadily since birds first bred in 1982, increasing agricultural conflict. Derogation shooting has been used since 2005 to scare geese from sensitive crops and to reduce population size. Numbers almost doubled to ca. 28 000 individuals during 2007-2014, despite annual removal of 15-25% of geese and adult and juvenile survival rates of 79 and 67% (cf. natural survival of 96% for both age classes). Simple population modelling, using estimated annual survival values and fixed fecundity, predicted a moderate increase to 21 500 individuals in 2014. It is unclear whether current harvest levels are sufficient to halt population growth. Shooting may be less effective because of the disproportionate take of immature post-breeding and of individuals from other populations in winter. Discrepancies between counted and modelled abundance call for caution and improved effect monitoring of derogation shooting before harvest levels are increased further.

Age-specific survival and annual variation in survival of female chamois differ between populations.

In many species, population dynamics are shaped by age-structured demographic parameters, such as survival, which can cause age-specific sensitivity to environmental conditions. Accordingly, we can expect populations with different age-specific survival to be differently affected by environmental variation. However, this hypothesis is rarely tested at the intra-specific level. Using capture-mark-recapture models, we quantified age-specific survival and the extent of annual variations in survival of females of alpine chamois in two sites. In one population, survival was very high (>0.94; Bauges, France) until the onset of senescence at approximately 7 years old, whereas the two other populations (Swiss National Park, SNP) had a later onset (12 years old) and a lower rate of senescence. Senescence patterns are therefore not fixed within species. Annual variation in survival was higher in the Bauges (SD = 0.26) compared to the SNP populations (SD = 0.20). Also, in each population, the age classes with the lowest survival also experienced the largest temporal variation, in accordance with inter-specific comparisons showing a greater impact of environmental variation on these age classes. The large difference between the populations in age-specific survival and variation suggests that environmental variation and climate change will affect these populations differently.