Consequences of differences in body mass, wing length and leg morphology for nectar‐feeding birds

Abstract

Nectar-feeding birds are prominent in many parts ofthe world, and vary with respect to body size. Despite the availability of considerable morphometric data, few concerted efforts have been made to assess the influence of attributes such as mass, wing length and leg morphology upon the speed, acceleration, mode and energetic cost of movement by birds between flowers when foraging for nectar. This review attempts to consolidate and interpret available data and highlight areas where further investigations appear warranted. Australian honeyeaters are generally larger, and American hummingbirds smaller, than Hawaiian honeycreepers and sunbirds of Africa or Asia. Sunbirds, honeyeaters and honeycreepers generally perch while extracting nectar from flowers. Hummingbirds usually hover, apparently because suitable perches close to flowers are lacking, and not because hovering increases the speed at which flowers can be visited. Honeyeaters move from one flower to another at speeds that are at least as great as those for hummingbirds. Most passerine nectarivores need to ingest more nectar per day than hummingbirds in order to maintain energy balance, some species devoting more than 60% ofthe day to foraging. The major consequence of reduced foraging activity by hummingbirds, which spend only 5-30% ofthe day in this manner, appears to be male emancipation from nest construction and care of offspring. Large nectarivores have a greater capacity to store surplus food and to fast than smaller birds, and so can take advantage of short-lived peaks in nectar abundance. Nectarivores such as honeyeaters should therefore be favoured by the rapid diurnal changes in nectar availability which are characteristic of many Australian and African habitats. Body mass also determines the likely access to rich sources of nectar through size-related interspecific dominance hierarchies. In all families, larger species tend to monopolize the most rewarding nectar supplies, forcing smaller subordinate species to use poorer, more scattered sources. Within particular species, males usually have longer wings and greater masses than females. These variations imply that the two sexes differ with regard to their foraging ecology, although few supporting data are currently available.

Why do some nectar foragers perch and others hover while probing flowers?

“…Figures 2a and b show that the transit time increased with the flight distance between the flowers as negatively accelerated functions in both species. Similar functions have been reported for hummingbirds (Wolf et al, 1976) and honeyeaters (Collins and Paton, 1989) and can probably be explained by a diminishing effect of the acceleration and deceleration with the distance flown. The flight time is considerably shorter in the hawkmoths than in the bumblebees at a given flight distance due to their faster mean flight speed (Fig.…”

“…On the other hand, a larger body size is an advantage in aggressive interactions and defence of resources, as has been observed many times (e.g. Colwell et al, 1974;Feinsinger and Chaplin, 1975;Primack and Howe, 1975;Collins and Paton, 1989). However, it is difficult to ascertain if a larger body size requires the evolution of resource defence, or just makes it possible.…”

African sunbirds hover to pollinate an invasive hummingbird-pollinated plant

“…The Trochilidae most often hover when feeding, and are superbly adapted to this mode of life, by having long, pointed wings, with long hands, light bodies, small feet, and long, straight bills (Collins and Paton 1989, Westerkamp 1990, Wells 1993, Altshuler and Dudley 2002, Warrick et al 2005, Iwaniuk and Wylie 2007, Tobalske et al 2007. In contrast, the nectarivorous birds of the Old World are Passeriformes, which seldom hover and never do so consistently (Pyke 1981, Westerkamp 1990, Fleming and Muchhala 2008.…”

Reproductive biology of the rare and endangered Banksia brownii Baxter ex R. Br. (Proteaceae)

“…Nevertheless, its influence would seem to be overridden to some extent in the case of B. brownii, because of the presence of relatively large numbers of flowers and inflorescences at different developmental stages on the same plants (Collins et al 1993(Collins et al , 1996. For this reason, nectarivorous pollinators should be able to satisfy their energy requirements without having to move frequently between plants (Collins & Paton 1989). In contrast, visitors to species such as B. attenuata and B. menziesii, which have relatively few inflorescences that are open and producing nectar at any one time, would be expected to move more often between plants (Ramsey & Vaughton 1991).…”