Abstract
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.
Highlights
Many species of wild geese have increased in numbers over recent decades as a result of changing agricultural practices and reduced harvest levels
The annual hunting bag resulting from derogation shooting in the Northern Delta area increased from 377 barnacle geese in 2005 to 5324 in 2014
From 2007 onwards, annual counts of all summering geese across Zuid-Holland, including the Northern Delta area, were made by volunteers and nature reserve wardens, coordinated by Centrum voor Landbouw en Milieu (CLM), an independent consultancy working in the field of sustainable food, farming and rural development (Tolkamp and Guldemond 2007, 2008, 2009; Visser et al 2010; den Hollander and Visser 2011, 2012; Keuper and Visser 2013, 2014)
Summary
Many species of wild geese have increased in numbers over recent decades as a result of changing agricultural practices and reduced harvest levels. Ranges of both wintering as well as breeding birds have increased or shifted (van Eerden et al 2005). In the Netherlands, the species became established as a breeding bird in 1982 (Meininger and van Swelm 1994; Ouweneel 2001; Lensink et al 2013), and the Dutch-breeding population has since grown to an estimated 13 800 breeding pairs by 2012 (Schekkerman 2012). The amount of damage to agricultural crops and grasslands by barnacle geese has increased in the area. The annual hunting bag (hb) resulting from derogation shooting in the Northern Delta area increased from 377 barnacle geese in 2005 to 5324 in 2014 (data obtained from Faunabeheereenheid Zuid-Holland). A colour-ringing scheme has been established in this area since 2004, with a total of 1109 geese being colour-ringed up to and including 2014, with an additional 313 geese receiving metal rings only
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