Hummingbirds' nectar concentration preferences at low volume: the importance of time scale

Roberts, Mark W.

doi:10.1006/anbe.1996.0180

Cited by 75 publications

(54 citation statements)

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“…Our observation of rapid lamellar unfurling rules out the idea that the hummingbird tongue tip acts as a set of static capillary tubes during nectar feeding (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)41). The tongue does not passively draw floral nectar up into the grooves via capillarity when its tips contact the liquid; rather, it is dynamically trapping nectar within the lamellae while the tips leave the fluid.…”

Section: Discussionsupporting

confidence: 60%

“…Our work with dead specimens demonstrates that neither the unfurling nor the furling of the lamellae requires any muscular work; the process of nectar trapping results purely from the structural configuration of the tongue tips. We are unaware of any other biological mechanism for fluid trapping that is similarly dynamic, yet Discovery of this dynamic nectar-trapping mechanism defies a consensus almost two centuries old, and has broad implications for our understanding of the evolution (16,23,43), energy budgets (24,29,44), foraging behavior (25,26,45), feeding mechanics (33,41,42), and morphology of the feeding apparatus (18,46,47) of hummingbirds. Our morphological survey documented the existence of the structures necessary for dynamic nectar trapping in species of hummingbirds representing all nine main clades in the family (cf.…”

Section: Discussionmentioning

confidence: 99%

“…Since then, all models of foraging strategy (including those predicting concentration preferences) and energy balance in hummingbirds have calculated calorie intake rate under the assumption that the tongue tip is in the form of a pair of semicylindrical grooves that fill passively via capillarity when in contact with the nectar (21)(22)(23)(24)(25)(26). The notion that fluid is drawn toward the mouth from the tongue tip and along the lingual grooves through the action of capillarity is currently widely accepted (19)(20)(21)(22)(23)(24)(25)(26)(27)(28). However, if capillarity were responsible for tongue loading, the aid of gravity should increase nectar-uptake rates at pendulous (downward facing) flowers, yet empirical work in recent years has failed to demonstrate any consistent correlation between nectar extraction rates and flower position (26,29).…”

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confidence: 99%

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The hummingbird tongue is a fluid trap, not a capillary tube

Rico‐Guevara

Rubega²

2011

Proc. Natl. Acad. Sci. U.S.A.

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Hummingbird tongues pick up a liquid, calorie-dense food that cannot be grasped, a physical challenge that has long inspired the study of nectar-transport mechanics. Existing biophysical models predict optimal hummingbird foraging on the basis of equations that assume that fluid rises through the tongue in the same way as through capillary tubes. We demonstrate that the hummingbird tongue does not function like a pair of tiny, static tubes drawing up floral nectar via capillary action. Instead, we show that the tongue tip is a dynamic liquid-trapping device that changes configuration and shape dramatically as it moves in and out of fluids. We also show that the tongue-fluid interactions are identical in both living and dead birds, demonstrating that this mechanism is a function of the tongue structure itself, and therefore highly efficient because no energy expenditure by the bird is required to drive the opening and closing of the trap. Our results rule out previous conclusions from capillarity-based models of nectar feeding and highlight the necessity of developing a new biophysical model for nectar intake in hummingbirds. Our findings have ramifications for the study of feeding mechanics in other nectarivorous birds, and for the understanding of the evolution of nectarivory in general. We propose a conceptual mechanical explanation for this unique fluid-trapping capacity, with far-reaching practical applications (e.g., biomimetics).biomechanics | fluid dynamics | nectar trapping | surface tension

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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The hummingbird tongue is a fluid trap, not a capillary tube

Rico‐Guevara

Rubega²

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…However, as previously noted, the value of Bo $ 0.2 indicates that gravitational effects are negligible in nectar uptake. Another potential inconsistency of the capillary model is that it predicts optimal nectar concentrations (30 -40%)-specifically those that maximize energy uptake rate-that are different from preferred concentrations (45 -60%), as deduced from the statistics of visit frequency to feeders with different nectar concentration [29,30]. However, a bird's preferred concentration may depend on factors such as gustatory preferences [31] or physiological state [32], and thus may not correspond to the optimal concentrations.…”

Section: Capillary Suction Versus Fluid Trappingmentioning

confidence: 99%

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

et al. 2012

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We present the results of a combined experimental and theoretical investigation of the dynamics of drinking in ruby-throated hummingbirds. In vivo observations reveal elastocapillary deformation of the hummingbird's tongue and capillary suction along its length. By developing a theoretical model for the hummingbird's drinking process, we investigate how the elastocapillarity affects the energy intake rate of the bird and how its open tongue geometry reduces resistance to nectar uptake. We note that the tongue flexibility is beneficial for accessing, transporting and unloading the nectar. We demonstrate that the hummingbird can attain the fastest nectar uptake when its tongue is roughly semicircular. Finally, we assess the relative importance of capillary suction and a recently proposed fluid trapping mechanism, and conclude that the former is important in many natural settings.

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“…Dilute bird nectars are puzzling since under laboratory conditions, both sunbirds and hummingbirds show preferences for more concentrated sugar solutions than their natural nectars, somewhere in the region of 31 to 45% (e.g. Stiles 1976, Pyke and Waser 1981, Tamm and Gass 1986, Roberts 1996.…”

Section: Watermentioning

confidence: 99%

Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions

2003

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Abstract. Nectarivory has evolved many times in birds: although best known in hummingbirds, sunbirds and honeyeaters, it also occurs on an opportunistic basis in a varied assortment of birds. We present a phylogenetic analysis of the distribution of nectarivory in birds. Specialised avian nectarivores are generally small, with an energetic lifestyle and high metabolic rates. Their high degree of dependence on nectar as a food source has led to convergence in morphological, physiological and behavioural adaptations. We examine the constituents of nectar which are most important to bird consumers, and how the birds deal with them in terms of physiology and behaviour. There are still unanswered questions: for example, the dichotomy between sucrose-rich nectars in hummingbirdpollinated plants and predominantly hexose-rich nectars in sunbird-pollinated plants appears to have little to do with bird physiologies and may rather reflect patterns of nectar secretion.

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Hummingbirds' nectar concentration preferences at low volume: the importance of time scale

Cited by 75 publications

References 0 publications

The hummingbird tongue is a fluid trap, not a capillary tube

The hummingbird tongue is a fluid trap, not a capillary tube

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

Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions

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