The Occurrence and Adaptive Significance of Nocturnal Habits in Waterfowl

Abstract

Summary This paper reviews the occurrence of nocturnal activity, particularly foraging, in wildfowl (Anseriformes) and shorebirds (Charadrii), and discusses its significance. Many duck species are mainly active at night while others regularly feed during both the day and night. Some ducks and geese are normally day feeders and occasionally forage during darkness. In a few duck species, courtship also has been observed at night. Most shorebirds forage both by day and night, in temperate and in tropical latitudes. Some are mainly crepuscular and nocturnal feeders and also display at dusk and at night. Some species may use their daytime territory at night. A few shorebird species, including some visual peckers and long‐billed tactile probers, use the same foraging method to detect and capture food by night as by day. However, some long‐billed species that forage visually during daytime modify their feeding techniques and rely completely or partly on tactile means for detecting prey at night. Large eyes seem an advantage to plovers and other sight feeders for night feeding. Numerous touch‐sensitive corpuscles in the bill of ducks and many scolopacid species favour tactile feeding. Some ducks, geese and shorebirds may especially use moonlit nights for feeding though, in a few species, moonlight seems to have no effect. The possible role of bioluminescence is also discussed. Nocturnal activity may occur for two reasons. The night may be preferred because foraging is more profitable or safest from predators. Alternatively, birds may be forced to forage at night because they fail to collect all their food requirements during the day. The evidence for both hypotheses is reviewed. Nocturnal activity does appear to allow wildfowl, and perhaps shorebirds, to avoid diurnal predators (including man). Shorebirds, and some ducks also seem to take advantage of prey that are more abundant and/or accessible at night. The main evidence for the supplementary feeding hypothesis comes from studies of seasonal variations in the occurrence of nocturnal feeding, about which rather little is known at present. The increasing availability of modern night‐viewing equipment may help to fill this gap. There are two important implications arising from the widespread occurrence of nocturnal activity in wildfowl. Most knowledge on time and energy budgets is based on daytime studies, and so may need to be revised. Wintering dabbling ducks and shorebirds, at least in some regions, may use different habitats by day and by night. If confirmed, there would be a need to preserve some wintering habitats which, although little used by ducks and shorebirds during the day, may be intensively used at night.

Hunting influences the diel patterns in habitat selection by northern pintails Anas acuta

“…These results support the preference hypothesis (McNeil et al 1992), which states that birds prefer to feed at night because it provides a safe feeding opportunity. Under the preference hypothesis, we expected to observe less selection for vegetation types related to feeding during the daylight hours and greater selection during night hours as potential threat to pintails increases.…”

“…For example, pintails have been observed using different areas during night hours than those during daylight, which has been associated with feeding at night and resting in flooded areas during the day (Lovvorn & Baldwin 1996). The three primary hypotheses that explain this behaviour are: 1) the preference hypothesis, 2) the supplementary hypothesis (McNeil et al 1992) and 3) the functional unit hypothesis. The preference hypothesis proposes that feeding areas are selected during night hours because this is a time when it is profitable and safe to forage.…”

Differences in the diurnal and nocturnal use of intertidal feeding grounds by RedshankTringa totanus

“…They may do so because they are unable to meet their daily energy requirements solely by foraging during the day (McNeil 1991, McNeil et al 1992. This may especially be the case for waders wintering at northerly latitudes, where short daylength and the influence of tides may restrict the time available for foraging (Goss-Custard 1969, Heppleston 1971.…”

“…This may especially be the case for waders wintering at northerly latitudes, where short daylength and the influence of tides may restrict the time available for foraging (Goss-Custard 1969, Heppleston 1971. Alternatively, birds may prefer to feed at night due to increased prey activity and availability of prey (Dugan 1981, Evans 1987, McNeil & Robert 1988, Mouritsen 1994 or a decreased risk of predation or disturbance (Robert et al 1989) (for a summary of hypotheses, see reviews by McNeil 1991, McNeil et al 1992. The extent of nocturnal foraging may also be influenced by moonlight (Heppleston 1971, Robert et al 1989, Dodd & Colwell 1998, although this may be more true for visual predators, such as plovers, than Calidris and Tringa spp., that are tactile feeders at night (Pienkowski 1981, McNeil & Robert 1988.…”

Time-activity budgets of wintering Ferruginous Duck, Aythya nyroca, at Gajoldoba wetland, Jalpaiguri, India

“…Why many species of waterfowl feed mainly at night is still unclear. Various explanations including avoidance of diurnal predators, food availability and the need to visually select food, and thermoregulation have been put forward (Jorde and Owen, 1988;McNeil et al, 1992;Green, et al, 1999). An otherwise nocturnal feeder, the Ferruginous Duck in the Gajoldoba wetland spent a considerable amount of diurnal time feeding, which indicates less human interference in the area.…”