Effects of body size, body fat, and change in pressure with depth on buoyancy and costs of diving in ducks (Aythya spp.)

Abstract

LOVVORN, J. R., and JONES, D. R. 1991. Effects of body size, body fat, and change in pressure with depth on buoyancy and costs of diving in ducks (Aythya spp.). Can. J. Zool. 69: 2879-2887. Recent studies of diving ducks (Aythya spp.) have shown that buoyancy is far more important to locomotor costs of shallow diving than is hydrodynamic drag. Working with Canvasbacks (A. valisineria), Redheads (A. americana), and Lesser Scaup (A. aflnis), we investi ated factors affecting buoyancy in models of locomotor energetics. Body volume can be accurately estimated from body mass ( rf = 0.82-0.95), but equations sometimes differ among species, and body volume relative to mass is higher in winter than in summer. Wing molt does not influence body volume or buoyancy. In scaup, an increase in body lipid from 35 to 190 g (from 5.4 to 22.3% of body mass) increases the energy costs of descent more through the inertial effects of higher mass and added mass of entrained water (82.8% of change) than through greater work against drag (12.0%) or buoyancy (5.2%). Costs of foraging at the bottom are 20% lower in the fatter birds because increased inertial resistance to the buoyant force is greater than the increase in buoyancy. Maximal changes in body lipid and associated hypertrophied muscle raise overall costs of diving to a depth of 2 m by only 2%. Such effects can be offset by altering respiratory and plumage air volumes (+I5 mL for a 155-g lipid increase) or the relative amount of time spent at the bottom. Hence, diving energetics contrast with the energetics of flight, which are strongly affected by body mass changes. Reduced buoyancy from compression of air spaces with depth lowers costs of bottom foraging in scaup by 24% at 1.2 m and 36% at 2 m. Mass-specific plumage air volume decreases with increasing body mass (slope = 0.12)' and body tissues are incompressible relative to air. Thus, buoyancy decreases faster with increasing pressure in smaller birds and they become negatively buoyant at shallower depths (about 43 m for Oldsquaws, Clangula hyemalis). Ducks such as eiders (Somateria spp.) weighing over 1200 g and diving to less than 60 m probably never become negatively buoyant. LOVVORN, J. R., et JONES, D. R. 1991. Effects of body size, body fat, and change in pressure with depth on buoyancy and costs of diving in ducks (Aythya spp.). Can. J. Zool. 69 : 2879-2887. Des etudes rkcentes sur les canards plongeurs (Aythya spp.) ont dkmontrk que la flottabilitk contribue beaucoup plus que la trainke hydrodynamique au coQt de la locomotion au cours de la plongke. Nous avons tent6 de dkteminer les facteurs qui affectent la flottabilitk en ktudiant des Morillons h dos blanc (A. valisineria), des Morillons h tCte rouge (A. americana) et des Petits Morillons (A. aflnis) et en intCgrant nos rksultats h des mod&les d'knergie locomotrice. Le volume du corps peut Ctre estimk justement d9apr&s la masse corporelle (2 = 0,82-0,97), mais les equations different parfois selon l'esp&ce et les rapportsvolume/masse sont plus ClevCs en hiver qu'en k...

Dive depth and plumage air in wettable birds: the extraordinary case of the imperial cormorant

“…We suggest, therefore, that the effects of depth are the primary driver for the observed differences between blue-eyed and other cormorants. Depth is important because depth-dependent pressure affects the volume of air in bird plumage (Lovvorn & Jones 1991), which in turn affects both the mechanical work required to overcome buoyancy (Lovvorn & Jones 1991, Lovvorn 1999, 2001) and heat loss (Gremillet et al 1998b, Enstipp et al 2006. Indeed, in a recent study, Wilson et al (2006) noted how overall dynamic body acceleration (ODBA) in great cormorants (as measured by animal-attached accelerometers) correlated closely (r 2 = 0.81) with rate of oxygen use, and how ODBA in free-living imperial cormorants correlated extremely well (r 2 = 0.97) with calculated relative buoyancy.…”

Variation in body condition during the post-moult foraging trip of southern elephant seals and its consequences on diving behaviour

“…), the buoyancy of an individual is determined primarily by its body composition, in particular, by the ratio of lipid to lean tissue (Crocker et al, 1997;Webb et al, 1998). Lean tissue is denser than seawater, whereas adipose tissue is less dense and, therefore, animals with a large proportion of lipid will be more buoyant (Beck et al, 2000;Lovvorn and Jones, 1991a;Lovvorn and Jones, 1991b;Nowacek et al, 2001;Webb et al, 1998). Elephant seals regularly perform dives during which they spend a large proportion of time descending passively through the water column ('drift dives').…”

Northern elephant seals adjust gliding and stroking patterns with changes in buoyancy: validation of at-sea metrics of body density

“…All three models quantify the influence of hydrodynamic drag and buoyancy on a passively moving body. Here, buoyancy is defined as the difference between the body density of the animal and that of the surrounding seawater (Lovvorn and Jones, 1991;Beck et al, 2000):…”