Abstract
Few long‐term, large‐scale studies have been conducted about the factors likely to explain changes in species abundance and distribution in winter. Range shifts are generally attributed to the climate change or land use. This study shows that other factors such as species protection and the ensuing increasing numbers of individuals and competition could be involved. It details the progressive conquest of France, the most important European wintering area for great cormorant, in three decades as its legal protection by the EU Birds Directive. It is based on 13 exhaustive national counts. Cormorants first occupied the farthest areas (Atlantic and Mediterranean lagoons, then larger rivers) from the main‐core European breeding area, with only progressive occupancy of the northeastern part later. This strategy mainly resulted from competition for optimal available feeding areas. Suboptimal areas (smaller wetlands harboring smaller night roosts, colder northeastern French areas) and progressive fragmentation of large night roosts into smaller, better located ones minimized flight costs. The coldest areas were occupied last, once other areas were saturated. Their occupancy was favored locally by the global climate change, but it played a minor role in these strategies. Both factors induced only a small NNE shift of the weighted centroid range of the wintering population (2.6 km/year) which mainly resulted from competition (buffer effect). Only the 2009 cold wave decreased the total number of wintering cormorants at the national scale, once the population had probably reached the carrying capacity of the country, while the previous cold waves had a minor effect. Comparatively, there was a greater SSE range shift of the weighted centroid of the breeding population (4.66 km/year). Range shifts of other recently protected species have been attributed to the sole climate change in the literature, but competition due to the saturation of usual wintering or breeding areas should be considered too.
Highlights
IntroductionNumerous studies have shown changes in the abundance and distribution of bird species mainly during the breeding season, owing to habitat destruction (Dolman & Sutherland, 1995), protection of species and habitats (Deinet et al, 2013), and more recently the climate change or new feeding resources (Adriaensen, Ulenaers, & Dhondt, 1993; Feare, 1994; Fiedler, 2003; Lindström, Green, Paulson, Smith, & Devictor, 2013; Loonen & De Vries, 1995; Merkel & Merkel, 1983; Møller, Fiedler, & Berthold, 2010; Nilsson & Persson, 2000; Schmidt, 1998; Visser, Perdeck, Van Balen, & Both, 2009; Wu & Zhang, 2015; Zuckerberg et al, 2011)
This study investigates the mechanisms of expansion of cormorant wintering populations in France and the changes in their distribution between 1983 and 2015 according to climate change and to competition for optimal areas
Our results show that year and department effects significantly explained the progressive evolution of cormorant site occupancy in France (68.87%)
Summary
Numerous studies have shown changes in the abundance and distribution of bird species mainly during the breeding season, owing to habitat destruction (Dolman & Sutherland, 1995), protection of species and habitats (Deinet et al, 2013), and more recently the climate change or new feeding resources (Adriaensen, Ulenaers, & Dhondt, 1993; Feare, 1994; Fiedler, 2003; Lindström, Green, Paulson, Smith, & Devictor, 2013; Loonen & De Vries, 1995; Merkel & Merkel, 1983; Møller, Fiedler, & Berthold, 2010; Nilsson & Persson, 2000; Schmidt, 1998; Visser, Perdeck, Van Balen, & Both, 2009; Wu & Zhang, 2015; Zuckerberg et al, 2011). Several studies about range shift were based on large multi-species databases of annual winter counts at large geographical scales They ascribed the latitudinal range shift to the climate change (Maclean et al, 2008; National Audubon Society 2014; Niven & Butcher, 2009; Potvin, Välimäki, & Lehikoinen, 2016, Visser et al, 2009); But they did not take into account each individual life history and the entire annual cycle, which are important to understand the mechanisms that underlie shifts as a real response to the climate change (Elmberg, Hessel, Fox, & Dalby, 2014; Knudsen et al, 2011; Lehikoinen, Saurola, Byholm, Lindén, & Valkama, 2010; Paprocki, Heath, & Novak, 2014; Potvin et al, 2016).
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