Pike predation affects breeding success and habitat selection of ducks

Abstract

1. Fish and ducks often belong to the same local food web, and several studies indicate that there is a general negative effect of fish on breeding ducks. This pattern has so far been addressed mainly within the framework of competition for common invertebrate prey, while predation by large fish as a force behind settlement and abundance patterns in ducks remains largely unknown. This is the first study to address the effect of fish predation on breeding ducks, isolated from that of competition, and the first experiment to explore the ability of ducks to identify and avoid lakes with high risk of fish predation. 2. We used a before-after control-impact design and 11 naturally fishless lakes. Waterfowl on the lakes were surveyed during the breeding season of 2005. Large adult pike (Esox lucius) were added to two lakes in early spring 2008, and waterfowl surveys were repeated on all 11 lakes. 3. Pike introduction did not affect the number of pairs on lakes during the nesting season in any of three focal duck species (mallard Anas platyrhynchos, teal Anas crecca, and goldeneye Bucephala clangula). During the brood-rearing season, however, there was a decrease in duck days in teal and goldeneye in lakes with pike, with similar trends observed in mallard. The number of goldeneye ducklings was also significantly lower in lakes with pike. We were unable to determine whether the response was attributable to direct pike predation or to broods leaving experimental lakes, but in either case, our study demonstrates high fitness costs for ducks breeding on lakes with pike. 4. The apparent inability of nesting ducks to detect pike and the clear fitness implications may influence the annual recruitment of ducks on a larger scale as pike are both common and widespread. Vegetation complexity and food abundance are likely to be of overriding importance when breeding ducks are choosing a nesting site. As pike have a strong influence on breeding birds, relying on vegetation and cues of food abundance, while ignoring indicators of predation risk from fish, could lead to lakes with pike acting as an ecological trap.

Ecosystem services provided by waterbirds

“…For example, over large areas red-throated diver Gavia stellata and Slavonian grebe Podiceps auritus almost never nest in lakes holding fish, and there is a strong negative correlation between overall species richness of breeding ducks and occurrence of fish in boreal lakes (e.g. Elmberg, Dessborn & Englund, 2010;Dessborn, Elmberg & Englund, 2011b). The distribution of breeding great northern divers G. immer is strongly related to a combination of the size of lakes and their fish production (Kerekes, 2008).…”

Reintroduction of a dioecious aquatic macrophyte (Stratiotes aloides L.) regionally extinct in the wild. Interesting answers from genetics

“…Considering that most of the variation was detected within populations, the similarity between populations belonging to different hydrographical basins could be explained through long‐distance bird‐mediated dispersal events, as first proposed by Forbes (), but not proved owing to the lack of direct or indirect observation of birds feeding on Stratiotes seeds (Dessborn et al ., ; L. Dessborn personal communication). Recently, coots ( Fulica atra ), which in some cases may perform long‐distance migrations, have been observed (in the Netherlands: Smolders, and in Russia: Efremov, personal observations) to eat S. aloides.…”

Fish stocking creates an ecological trap for an avian predator via effects on prey availability

“…While 0+ carp were a major prey item for chicks, interactions with 1+ carp shifted with time, from predation by adult birds on carp to competition and related adverse influence of carp on chicks (Kloskowski 2011). Apparently, when fish and birds interact in complex ways, the cues related to fish can be ambiguous (see also Dessborn et al 2011). This renders birds more prone to make inappropriate habitat decisions with respect to perceived food availability when alterations in a system generate novel trophic dynamics.…”

“…Indeed, most amphibian species avoided ponds containing large fish, but adults of the earliest‐breeding anurans were relatively common in ponds with ≥ 1+carp (Kloskowski 2011). However, given that fish can be a strong competitor for waterbirds (Wagner and Hansson 1998, Haas et al 2007), the question arises as to why grebes do not show preference for fishless ponds or at least select against habitats dominated by fish which are inedible for chicks by virtue of their large size (see also Dessborn et al 2011). Fishless habitats provide a secure option due to development of rich invertebrate and amphibian faunas, used by grebes as resources equivalent to fish (Wagner and Hansson 1998, McParland and Paszkowski 2006).…”