Bills and tongues of nectar‐feeding birds: A review of morphology, function and performance, with intercontinental comparisons

Abstract

The bills and tongues of nectar-feeding birds differ from continent to continent. The major differences are that: (i) the tongues of 4 tistralian honeyeaters are broader any more ftmbricated at the tip than the bifurcated tongues of sunbirds and hummingbirds; (ii) ihe bills of hummingbirds are more uniformly narrow and taper less markedly towards their tips than tiiose of sunbirds and honeyeaters: and (iii) bill curvatures are generally greater for sunbirds and honeycreepers than for hummingbirds. A variety of hummingbirds has straight or even slightly upturned bills, while bills for all sunbirds, honeycreepers and honeyeaters are decurved to some extent. Despite differences in tongue morphology, hummingbirds, sunbirds and honeyeaiers extract nectar at a similar range of rates, averaging approximately 40 fiE s~ 'from ad libitum feeders, and 1-15~' from flowers. All tongues collect nectar by capillarity, with licking rates of 6-17 s~'. Eicking behaviour has been little studied, although speeds of licking respond to changes in sugar conceniraiion and corolla length. The tongues of honeyeaters are broad, and may need to be brush-lipped in order to allow capillary collection of neeiar. Brush-tipped tongues can cover large surface areas on each lick, and may allow honeyeaters io exploit nectar and honeydew thai is thinly spread over large surfaee areas. Bill lengths of neciarivorous birds are similar in all regions, though species of hummingbird have the shortest and longest bills. Bill lengths largely determine the range of floral lengths ihal can be legitimately probed. Maximum floral lengths exceed bill lengths, since hummingbirds, sunbirds and honeveaters protrude iheir tongues beyond the tips of their bills. Rates of nectar extraction, however, decline rapidly once the floral length exceeds bill length. Decurved bills may have evolved in honeyeaters and sunbirds lo enable perching birds lo reach flowers al the ends of branches more easily. Consistent differences in bill length between the sexes suggest that males and females may exploit different floral resources or different proportions ofthe same resources. For honeyeaters and sunbirds, males have longer bills than females, bul the reverse is true for many hummingbirds.

Morphological Comparison of the Filiform Papillae of New Zealand White Rabbits (Oryctolagus cuniculus) as Domestic Mammals and Egyptian Fruit Bat (Rousettus aegyptiacus) as Wild Mammals Using Scanning Electron Microscopic Specimens

“…There are some variation in the lingual adaptation between the New Zealand white rabbits (domestic mammals eating directly from the ground) and the Egyptian fruit bat (wild mammals eating during the flight), this adaptation is clear in the our study in the Egyptian fruit bat; firstly, the tongue tip not have giant filiform papillae and instead a blunt small filiform papillae, in which this distribution may have an important role in feeding habits, this confirmed by (Hall et al, 1995), while (Paton & Collins, 1989) in nectar-feeding bats, noted that the functions of giant filiform papillae on the tongue tip to increase the surface area to collect nectar. The another adaptation, the giant filiform papillae were rough to touch to help in power catching by piercing the skin of soft fruits to consume fruit and press it between the tongue the ridged hard palate to release the juices (Bonaccorso & Gush, 1987).…”

The hummingbird's tongue: a self-assembling capillary syphon

“…The tongue must be flexible for this unloading process. In addition, when only small quantities of nectar are available in the target flowers, a flexible tongue may make it easier for the tongue lamellae to sweep the corolla tube [11,25]. Hummingbirds feed from plants with a variety of floral morphologies; jewelweed (Impatiens capensis) even has forward-pointing nectar spurs that require the tongue to bend at a 1808 angle [26].…”

“…Thus, the detailed shape of the hummingbird's tongue may also be affected by the corolla morphology and nectar attributes of its target flowers. Nevertheless, flexible tongues with semicircular cross-sectional shapes are characteristic of many hummingbirds, as well as sunbirds and honeyeaters [25], which may rely on similar nectar uptake styles.…”

Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds

“…The highly signi¢cant correlation between measurements for taxa in both museum and literature data ( p 5 0.001) suggests that the quality of information from di¡erent sources is comparable and that these data can reasonably be combined. Sexual dimorphism in bill length was calculated as the ratio of mean female to mean male bill length ( 41 in most hummingbird species; Paton & Collins 1989). I also obtained data on body-mass sexual dimorphism for 106 of these same species to examine body-mass e¡ects on BLSD.…”

“…Hummingbirds (Trochilidae) have evolved sexual dimorphism in many of their characteristic attributes, including plumage coloration, bill morphology and foraging strategy. A strong case can be made that the hummingbird bill is a paradigm of ecological adaptation, as both experimental and observational studies suggest that characteristics of the bill are directly related to £ower feeding (Feinsinger & Colwell 1978;Paton & Collins 1989;Temeles 1996;Temeles & Roberts 1993). However, hummingbird foraging behaviours are also strongly tied to reproductive behaviours because competitors and £oral densities determine if males hold nectar-centred breeding territories or adopt alternative mating strategies (Pitelka 1942;Stiles & Wolf 1979;Payne 1984).…”