Wetland use by brood-rearing female ducks in a boreal forest landscape: the importance of food and habitat PETRI NUMMI, 1 * ANTTI PAASIVAARA, 2 SARI SUHONEN 1 & HANNU PÖYSÄ 3 1 Department of Forest Sciences, University of Helsinki, PO Box 27, Helsinki, FI-00014, Finland 2 Oulu Game and Fisheries Research, Finnish Game and Fisheries Research Institute, Tutkijatie 2 E, Oulu, FI-90570, Finland 3 Joensuu Game and Fisheries Research, Finnish Game and Fisheries Research Institute, Yliopistokatu 6, Joensuu, FI-80100, Finland Habitat use by birds may be related to single or interacting effects of habitat characteris- tics, food resources and predators, but little is known about factors affecting habitat use by wetland species in boreal ecosystems. We surveyed brood-rearing females and duck- lings of four common boreal duck species to assess the effects of habitat structure and food resources on the use of wetlands by brood-rearing ducks. Although wetland use by duck broods was related to habitat structure and food abundance, their relative impor- tance varied among duck species. For the Common Goldeneye Bucephala clangula, a div- ing duck, aquatic invertebrates and large emerging insects were the most important factors associated with wetland use. Common Teal Anas crecca broods were observed more often on wetlands with greater Dipteran emergence, whereas in Mallard Anas platyrhynchos both habitat structure and large emerging insects were important. The occurrence of Eurasian Wigeon Anas penelope broods was related to emerging Diptera and habitat structure but the associations were not strong. The varying habitat and food requirements of common duck species could influence the success of wetland manage- ment programmes, and consideration of these factors may be particularly important for initiatives aimed at harvested species or species of conservation concern. Keywords: Anas crecca, Anas penelope, Anas platyrhynchos, aquatic invertebrates, Bucephala clangula, emerging insects, habitat structure. Understanding factors that affect the distribution of species and individuals among habitats is crucial for effective management and conservation. However, associations between habitat structure and habitat use may be difficult to interpret because different habitat characteristics often act at the same time, confounding the effects of individual factors (Petit & Petit 1996, Chalfoun & Martin 2007). The relative importance of food and habitat structure is frequently addressed in studies of habitat selection by birds (Wiens 1989, Preston 1990, Butler & Gil- lings 2004) and some researchers have argued that the importance of structure per se has been overemphasized (Cody 1981, Terborgh 1985). Ter- borgh (1985) pointed out that the ‘seductive corre- lations’ found between birds and the structural complexity of their habitat may be mere reflections of some critical habitat features which are not read- ily measured and which closely correlate with habi- tat structure – of which food resources are a good example (Halaj et al. 2000). Temporal variation in critical resources may pose difficulties for birds that must attempt to predict future habitat quality. General habitat structure, for example, may be detectable early in the breeding season, but not the variation in insect food abundance and availability (Hilden 1965, Orians & Wittenberger 1991). Waterbirds live in environments where habitats and resources are patchily distributed. In boreal *Corresponding author. Email: petri.nummi@helsinki.fi © 2012 British Ornithologists’ Union Ibis (2013), 155, 68–79