Foraging Depth Research Articles

Diving and Feeding Behaviour of Sperm Whales (<I>Physeter macrocephalus</I>) in the Northwestern Mediterranean Sea

Sperm whale (Physeter macrocephalus) is one of the common cetacean species inhabiting the western Mediterranean Sea. The aim of this study was to describe the dive cycle of sperm whales in this region and gain insight into their foraging activity. Dedicated summer field seasons were conducted from 2001-2003. Visual and acoustic measures were undertaken and their relationships analyzed. The measures included surface/dive periods, blow rate, distance traveled, timing of clicks & creak activity, and inter-pulse interval measurements of sperm whale clicks. The whales exhibited dive cycle parameters consistent with those measured in other parts of the world: approximately 45 min dive duration, 9 min surface period (i.e., inter-dive interval), with 5 blows/min, and 1.3 nmi horizontal displacement between dives. An average of 25 creaks per dive were registered. Whale body size appeared to be significantly related with both the number of creaks per dive and the dive time at which the first creak occurred, suggesting that larger whales may increase their prey intake and use deeper water layers than smaller whales. The timing of the first creak and the last click of the dive (around 6 min after fluke-up, and just before the surfacing, respectively) suggest a foraging depth of between 500 and 800 m, based on known descent and ascent rates.

Inspiration by Magellanic penguins: reduced swimming effort when under pressure

Some marine mammals may increase their underwater locomotor efficiency by taking down little air for dives and descending passively, although at the point of maximum depth they presumably have to use energy to counteract the downthrust, to stop themselves sinking further. Birds, having considerable quantities of body-associated air, would appear not to have this option. However, measurements of locomotor activity and inspiratory behaviour of free-living, diving penguins has revealed that birds regulated the inspired air volume so that upthrust, primarily derived from depth-related changes in air volume, was minimal and constant at the preferred foraging depth. Although this results in minimized costs of travel, it means total body oxygen stores have to vary with depth, something that helps explain why dive duration is so closely correlated with depth in birds.

Optimal choice of foraging depth in divers

When prey availability depends on water depth, a diver should choose an optimal depth for foraging. A model that predicts the optimal foraging depth for a diver is presented in this paper. General predictions derived from the model are: (1) optimal foraging depth is always shallower than the depth at which prey density is the highest, even if the depth of the highest prey density is within easy reach; (2) a larger diver should make deeper and longer dives and stay longer on the surface than smaller divers for optimal foraging; (3) foraging efficiency of larger divers is not always greater than smaller divers, although the larger divers forage at the depth of higher prey density. These predictions, derived from the model, are consistent with the comparative studies of diving behaviour in marine birds.

Optimal choice of foraging depth in divers

AbstractWhen prey availability depends on water depth, a diver should choose an optimal depth for foraging. A model that predicts the optimal foraging depth for a diver is presented in this paper. General predictions derived from the model are: (1) optimal foraging depth is always shallower than the depth at which prey density is the highest, even if the depth of the highest prey density is within easy reach; (2) a larger diver should make deeper and longer dives and stay longer on the surface than smaller divers for optimal foraging; (3) foraging efficiency of larger divers is not always greater than smaller divers, although the larger divers forage at the depth of higher prey density. These predictions, derived from the model, are consistent with the comparative studies of diving behaviour in marine birds.

Packages for Attachment to Seabirds: What Color Do Adelie Penguins Dislike Least?

We attached black, white, blue, red, and yellow packages containing a peck pressure sensor and recorder to the dorsal feathers of free-living Adelie penguins (Pygoscelis adeliae). Packages were left in place for up to 14 days. Black packages, which matched the background feather color, were pecked significantly less (P < 0.05) than any other color except red during 24-hour trials with incubating birds. Other colors were pecked equally. The number of pecks given to packages worn at sea was positively related to the wearing time with no evidence of habituation up to the maximum wearing period. Researchers equipping penguins with external devices will have to consider device coloration as a potentially important source of irritation to the birds. J. WILDL. MANAGE. 54(3):447-451 The foraging habits of many seabirds are obscure due to the difficulty of observing birds at sea. However, attaching telemetric and other remote-sensing devices enables aspects of seabird marine ecology to be studied without direct observation. These devices have been used to de ermine avian foraging depths (Kooyman et al. 1982, Burger and Simpson 1986), foraging ranges and traveling speeds (Adams and Wilson 1987), dive duration (Trivelpiece et al. 1986), and total time spent underwater (Cairns et al. 1987). 'Present address: Centre d'Etudes Biologique des Animaux Sauvages, Centre National de Recherche Scientifique, 79360 Beauvoir sur Niort, France. This content downloaded from 157.55.39.223 on Wed, 24 Aug 2016 03:52:30 UTC All use subject to http://about.jstor.org/terms 448 PACKAGE COLOR * Wilson et al. J. Wildl. Manage. 54(3):1990 The necessity of packages to determine behavior of animals that cannot be observed also often precludes the possibility of directly assessing package-induced aberrant behavior (Perry 1981). Packages may affect seabirds either by physically impairing their capabilities, e.g., by reducing swimming speeds (Wilson et al. 1986) or by inducing extended time spent preening or trying to remove the device. Wilson and Wilson (1989a) described a simple device that uses a carbon paper sensor to determine the number of times that a packagefitted bird pecks at the device. We used this system to examine whether the reaction of breeding Adelie penguins to attached packages varied with the color of the package. We thank the Instituto Antartico Argentino for providing logistic help. Funding was provided by the Deutsche Forschungsgemeinschaft grant MZ/Ad 24/11-1. We are grateful to M.-P. Wilson for comments on the manuscript.

Population Dynamics and Bioenergetics of a Fossorial Herbivore, Thomomys talpoides (Rodentia: Geomyidae), in a Spruce‐Fir Sere

Studies of the bioenergetics of the northern pocket gopher, Thomomys talpoides, are coupled with data on demography, activity budgets, and microclimates to model the energy requirements of individuals and populations in the Wasatch Mountains of Utah during 1976—1979. Metabolic rates during rest increased linearly with decreasing ambient temperature, but burrowing metabolic rates (16.3 mL O2°h—1°g—0.75) were independent of both temperature and physical properties of the soil. Radio—telemetry studies indicated that free—ranging gophers are active °50% of each day. Conservative estimates of true energy consumption were calculated using estimates of habitat—specific minimum daily burrowing requirements. Rates of burrowing measures in the laboratory were either °0.0 or °2.0 cm/min. The low burrowing rate was observed when the soil was frozen or saturated with water, as would occur in the field in early winter and in spring, respectively. Gophers burrowed through soil at the study site at an average rate of °1.5 cm/min. Belowground food energy densities at gopher foraging depth declined from 24.6 to 3.2 J/cm3 along a successional gradient (subalpine forb meadow to Engelmann spruce dominated forest). We conclude that individual gophers are food limited within the climax spruce seral stage. Further, daily energy costs associated with reproduction in females may exceed the belowground energy supply available in intermediate seral stage (aspen and subalpine fir). Reduction of burrowing rates for any reason will affect gophers in the late seral stages proportionately more than those resident in the meadow. The peak gopher densities recorded (from 62 individuals/ha in the meadow to 2 individuals/ha in spruce forest) support these inferences. Detailed demographic information was obtained only in the meadow seral stage. Adult survivorship was lower in winter than in summer and varied greatly between years (0.18—0.70 yr—1). Juvenile survivorship from weaning through the first winter was comparable to adult annual rates. The fertility rate was 3.75 young°female—1°yr—1. The energy supply and demand analyses indicate that the growth of Thomomys talpoides populations in the early seral stages is seldom directly limited by the amount of food present. From our demographic, environmental, and autecological studies we conclude that stochastic events associated with weather affect energy acquisition (burrowing) rates, and thus survivorship. In montane environments, such events may prevent populations from attaining sizes at which territorial behavior would hypothetically limit further increases. The energy flow through the meadow population at moderate to high (1976—1977) densities (at least 1100 MJ°ha—1°yr—1) indicates that pocket gophers are proficient energy movers relative to nonfossorial small mammals. Subalpine T. talpoides populations appear commonly to attain such densities. More than 30% of the annual primary productivity allocated to belowground parts of meadow forbs may be consumed by gophers.