Effect of flower shape and size on foraging performance and trade‐offs in a tropical hummingbird

Abstract

Abstract. Matches between the bills of hummingbirds and the flowers they visit have been interpreted as examples of coadaptation and feeding specialization. Observations of birds feeding at flowers longer or shorter than their bills combined with a lack of experimental evidence for foraging trade-offs, however, fail to support these interpretations. We addressed these inconsistencies by considering a seldom-studied dimension of hummingbird-flower relationships, the shape of bills and flowers, through experiments on the Purple-throated Carib, Eulampis jugularis, and its major food plant, Heliconia, in the eastern Caribbean. Bills of male E. jugularis are considerably shorter and straighter than bills of females. We examined foraging performances and trade-offs during visits to natural heliconias and 34 artificial flowers of differing length and curvature. Supporting predictions based on matches between bill and flower morphology, handling times of females were significantly shorter than those of males at the long, curved flowers of a green morph of H. bihai. Contrary to predictions, handling times of males were not significantly shorter than handling times of females at the short flowers of H. caribaea. At artificial flowers, maximum extraction depths of females were significantly longer than maximum extraction depths of males at all curved flowers, but not at straight flowers. Handling times of females were significantly shorter than handling times of males at the longest artificial flowers for all curvatures, whereas handling times of males were significantly shorter at short, straight, artificial flowers, but only while hover-feeding without a perch. Within each sex, handling times were inversely related to bill length at long flowers for all shapes. Taken together, these performance trade-offs suggest that the long, curved bills of females are adapted for feeding from long, curved flowers, whereas the short bills of males are adapted for hover-feeding from short, straighter flowers. In addition, the finding that differences in feeding performance occur at the extremes of floral phenotypes suggests that the evolution of bill morphology may be driven by a small subset of the flowers visited by a hummingbird species.

Phylogenetic structure in tropical hummingbird communities

“…Hummingbirds are the most specialized nectar-feeding birds in the New World and often compete aggressively for nectar resources (23)(24)(25)(26). Bill morphology varies substantially in curvature and length and often influences what nectar resources are used (27). Wing shape and bill morphology influence flight ability and foraging efficiency and have been proposed to determine community organization (23,24,28,29).…”

Untangling the influence of ecological and evolutionary factors on trait variation across hummingbird assemblages

“…This may indicate that biotic interactions are particularly intense when the range of trait values (i.e., VAR) in a given assemblage is reduced, forcing traits to be evenly spaced across the existing, somewhat limited, morphospace. The efficiency with which hummingbirds extract resources from flowers is partly determined by the morphological fit between flower corolla length and hummingbird culmen length (Hainsworth 1973, Stiles 1975, Gutie´rrez-Zamora et al 2004, Temeles et al 2009). In stressful environments, such as mountains, efficient use of resources may be particularly important, and this could lead to relatively closely matched culmen-corolla lengths (Stiles 2008), which in turn may explain the even dispersion of bill size in high cold environments.…”

“…At high elevations, hovering flight is more difficult due both to lack of oxygen and a decrease in air density (Feinsinger et al 1979, Altshuler et al 2004, Altshuler and Dudley 2006, which results in montane birds having larger wings (Feinsinger et al 1979, Altshuler and Dudley 2002, Stiles 2008. The length and shape of the beak has long been known to be associated with resource use by hummingbirds and the efficiency with which nectar is extracted from flowers , Hainsworth 1973, Temeles et al 2009), but it remains unclear why one form or another might be at a selective advantage at different elevations.…”

Plant–pollinator interactions and floral convergence in two species of Heliconia from the Caribbean Islands

“…In Caribbean Heliconia, floral isolation is observed on the island of Dominica, where both structural differences in flower morphology and pollinator preferences determine effective pollination by either male or female purple-throated caribs (Temeles et al 2009). However, this situation does not occur on Hispaniola, where there are no morphological differences between Heliconia species that would promote pollen placement on different parts of the pollinator's body.…”

“…Second, the Caribbean Islands are moderately isolated from each other; therefore, limited gene flow among islands might favor the evolution of stable, locally-adapted variants. Third, comprehensive studies of plant-pollinator interactions, floral ecology, and hummingbird behavior are available for various islands of the Lesser Antilles, providing baseline information for comparative studies (Temeles et al 2000(Temeles et al , 2005(Temeles et al , 2009Temeles and Kress 2003;Gowda 2009. Earlier studies on the islands of St Lucia and Dominica showed a strong association between Heliconia floral phenotypes and the bills and energy requirements of their sexually-dimorphic hummingbird pollinator, the purplethroated carib (Eulampis jugularis) (Temeles et al 2000;Temeles and Kress 2003). Heliconia bihai has long, curved flowers that are pollinated by female purple-throats, whereas H. caribaea has shorter and straighter flowers that are pollinated primarily by male purple-throats (Temeles and Kress 2003; Fig.…”