Natural drinking strategies

Abstract

<jats:title>Abstract</jats:title><jats:p>We examine the fluid mechanics of drinking in nature. We classify the drinking strategies of a broad range of creatures according to the principal forces involved, and present physical pictures for each style. Simple scaling arguments are developed and tested against existing data. While suction is the most common drinking strategy, various alternative styles have evolved among creatures whose morphological, physiological and environmental constraints preclude it. Particular attention is given to creatures small relative to the capillary length, whose drinking styles rely on relatively subtle interfacial effects. We also discuss attempts to rationalize various drinking strategies through consideration of constrained optimization problems. Some biomimetic applications are discussed.</jats:p>

Hummingbird tongues are elastic micropumps

“…The tongue of a hummingbird features paired longitudinal grooves running from near the tip to mid-tongue (figure 1); these grooves in their relaxed state resemble open cylinders, which is the reason why meniscus-driven (capillarity) equations have been invoked. Capillarity equations have been used to infer optimal concentrations in the nectar produced by bird-pollinated plants [9][10][11], optimization in drinking behaviours of nectarfeeding animals [12] and fluid transport optimality in a variety of natural and artificial systems [13]. However, during five years of high-speed filming of free-living hummingbirds, we accrued the most comprehensive dataset of tongue-nectar interactions reported to date, and both our qualitative and quantitative analyses show that capillarity cannot account for either the tongue dynamics, or for the rate at which nectar fills the grooves in unmanipulated hummingbirds feeding in the wild.…”

Optimal concentrations in transport systems

“…Owing to the cost of constructing and maintaining redundant channels, it is advantageous for biological transport systems to distribute matter efficiently [1,2]. Oxygen transport in vertebrates [3,4], sugar transport in plants [5] and drinking strategies of many animals [6,7] are known to be optimized for efficient transport of energy and material. Engineered systems must likewise be cost-effective and able to provide efficient transport under a variety of conditions; for example, considerable resources are spent annually to ease traffic congestion.…”

Remnants from fast liquid withdrawal

“…8,22 Yet, the question of the amount of liquid remaining adherent to the pulling rods has been eluded so far. Remnants adhering to a solid are relevant to all situations where an object immersed in a wetting liquid is quickly removed from it, and has obvious bearings on surface coating and cleaning, 23,24 animal feeding, 22,25 or metrology, [26][27][28] for example. This question has received answers when viscous stresses are balanced by capillarity in various forms of the Landau-Levich problem, 29 while we address here a situation where inertia and capillarity are solely at play: We study the breakup of an axisymmetric low viscosity liquid volume (ethanol and water), held by surface tension on supporting rods, when subject to a vigorous and reproducible axial stretching either at constant acceleration (up to 100g, with g = 9.81 m/s 2 ), or constant velocity (up to 10 m/s).…”