Long-distance Foraging Research Articles

Post-nesting migrations of loggerhead sea turtles in the Gulf of Mexico: dispersal in highly dynamic conditions

This study is the first report of post-nesting migrations of loggerhead sea turtles (Caretta caretta) nesting in Sarasota County (Florida, USA), their most important rookery in the Gulf of Mexico (GOM). In total, 28 females (curved carapace length CCL between 82.2 and 112.0 cm) were satellite-tracked between May 2005 and December 2007. Post-nesting migrations were completed in 3–68 days (mean ± SD = 23 ± 16 days). Five different migration patterns were observed: six turtles remained in the vicinity of their nesting site while the other individuals moved either to the south-western part of the Florida Shelf (n = 9 turtles), the Northeast GOM (n = 2 turtles), the South GOM (Yucatan Shelf and Campeche Bay, Mexico, and Cuba; n = 5 turtles) or the Bahamas (n = 6 turtles). In average, turtles moved along rather straight routes over the continental shelf but showed more indirect paths in oceanic waters. Path analyses coupled with remote sensing oceanographic data suggest that most of long-distance migrants reached their intended foraging destinations but did not compensate for the deflecting action of ocean currents. While six out of seven small individuals (CCL < 90 cm) remained on the Florida Shelf, larger individuals showed various migration strategies, staying on the Florida Shelf or moving to long-distance foraging grounds. This study highlights the primary importance the Western Florida Shelf in the management of the Florida Nesting Subpopulation, as well as the need of multi-national effort to promote the conservation of the loggerhead turtle in the Western Atlantic.

Walking on inclines: how do desert ants monitor slope and step length.

BackgroundDuring long-distance foraging in almost featureless habitats desert ants of the genus Cataglyphis employ path-integrating mechanisms (vector navigation). This navigational strategy requires an egocentric monitoring of the foraging path by incrementally integrating direction, distance, and inclination of the path. Monitoring the latter two parameters involves idiothetic cues and hence is tightly coupled to the ant's locomotor behavior.ResultsIn a kinematic study of desert ant locomotion performed on differently inclined surfaces we aimed at pinpointing the relevant mechanisms of estimating step length and inclination. In a behavioral experiment with ants foraging on slippery surfaces we broke the otherwise tightly coupled relationship between stepping frequency and step length and examined the animals' ability to monitor distances covered even under those adverse conditions. We show that the ants' locomotor system is not influenced by inclined paths. After removing the effect of speed, slope had only marginal influence on kinematic parameters.ConclusionFrom the obtained data we infer that the previously proposed monitoring of angles of the thorax-coxa joint is not involved in inclinometry. Due to the tiny variations in cycle period, we also argue that an efference copy of the central pattern generator coding the step length in its output frequency will most likely not suffice for estimating step length and complementing the pedometer. Finally we propose that sensing forces acting on the ant's legs could provide the desired neuronal correlate employed in monitoring inclination and step length.

Historical and ecological determinants of genetic structure in arctic canids

Wolves (Canis lupus) and arctic foxes (Alopex lagopus) are the only canid species found throughout the mainland tundra and arctic islands of North America. Contrasting evolutionary histories, and the contemporary ecology of each species, have combined to produce their divergent population genetic characteristics. Arctic foxes are more variable than wolves, and both island and mainland fox populations possess similarly high microsatellite variation. These differences result from larger effective population sizes in arctic foxes, and the fact that, unlike wolves, foxes were not isolated in discrete refugia during the Pleistocene. Despite the large physical distances and distinct ecotypes represented, a single, panmictic population of arctic foxes was found which spans the Svalbard Archipelago and the North American range of the species. This pattern likely reflects both the absence of historical population bottlenecks and current, high levels of gene flow following frequent long-distance foraging movements. In contrast, genetic structure in wolves correlates strongly to transitions in habitat type, and is probably determined by natal habitat-biased dispersal. Nonrandom dispersal may be cued by relative levels of vegetation cover between tundra and forest habitats, but especially by wolf prey specialization on ungulate species of familiar type and behaviour (sedentary or migratory). Results presented here suggest that, through its influence on sea ice, vegetation, prey dynamics and distribution, continued arctic climate change may have effects as dramatic as those of the Pleistocene on the genetic structure of arctic canid species.

Social, state-dependent and environmental modulation of faecal corticosteroid levels in free-ranging female spotted hyenas.

Little is known about to what extent the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis may be state dependent and vary in the same species between environments. Here we tested whether the faecal corticosteroid concentrations of matrilineal adult female spotted hyenas are influenced by social and reproductive status in adjacent ecosystems and whether they vary between periods with and without social stress. Females in the Serengeti National Park frequently become socially subordinate intruders in other hyena territories by undertaking long-distance foraging trips to migratory herds, whereas in the Ngorongoro Crater they usually forage inside their own small territories on resident prey. The faecal corticosteroid concentrations in Serengeti females were significantly higher than in Ngorongoro females. Energy expenditure by lactation is exceptionally high in spotted hyenas and this may be reflected in their corticosteroid levels. The faecal corticosteroid levels in both populations were higher in lactating than in non-lactating females. During periods of social stability, faecal corticosteroid concentrations increased in non-lactating females but not in lactating females as social status declined. Lactating Serengeti females had significantly higher faecal corticosteroid concentrations during periods with acute severe social stress than during periods without, indicating that the HPA axis is sensitive to social stimuli even in lactating females. So far few studies have used non-invasive monitoring methods for assessing social stress in freeranging animals. This study demonstrates for the first time, to the authors' knowledge, that corticosteroid concentrations may differ between periods with and without social stress for a free-ranging female mammal and that the modulating effect of social status may depend on reproductive status.

Nutritional Condition and Muscular Features of Wintering Long-Billed Murrelets in Japan

Abstract We analyzed the nutritional condition and morphological characteristics of wintering Long-billed Murrelets (Brachyramphus perdix) in Japan. These birds were well nourished with an average body mass of 293 g, composed of a mean total body fat of 40.7 g (14%). The fat deposit was equivalent to an average energy reserve of 2.5 days at the estimated energy consumption of 615 kJ day−1 or 2.1 kJ g−1 day−1. Muscle mass consisted mainly of water (73%) and fat-free dry matter (26%), with small amounts of fat. Uropygial glands consisted of 33% fat and 17% fat-free dry matter, with 48% water. Long-billed Murrelets were characterized by large pectoral (26% of fat-free body mass) and small leg muscles (2% of fat-free body mass). We believe that these muscular traits, which contrast with those of alcids breeding at coastal colonies, reflect specific adaptations to inland nesting and long-distance foraging. Condicion Nutricional y Caracteristicas Musculares durante el Periodo de Invernada de Brachyramphus perdi...

Pellet and bone accumulation at a colony of Western Gulls (Larus occidentalis)

Pellet and bone accumulation at a colony of Western Gulls (<i>Larus occidentalis</i>)

FORAGER BEHAVIOR, POLLEN DISPERSAL, AND INBREEDING IN TWO SPECIES OF HUMMINGBIRD-POLLINATED PLANTS.

In animal-pollinated plant species, behavior is known to affect pollen dispersal (Bateman, 1947; Wright, 1951; Levin, 1981; Handel, 1983b). These observations have led to the prediction that behavior can have important effects on the genetic structure of plant populations. This prediction has been validated indirectly both by broad surveys of many plant taxa pollinated by a variety of animals with differing foraging patterns (Hamrick et al., 1979; Loveless and Hamrick, 1984) and by surveys of foraging patterns and resulting pollen dispersal in individual plant taxa (Levin and Kerster, 1974; Levin, 1981; Handel, 1983b). Still needed are comparative analyses of closely related taxa in order to isolate and understand the effects of specific features of life histories upon such structure (Loveless and Hamrick, 1984). In this study of two species of closely related tropical herbs, we provide evidence that differences in hummingbird foraging behavior and associated gene flow generate differences in levels of inbreeding of the plant populations concerned. Razisea spicata and Hansteinia blepharorachis (Acanthaceae) are perennial understory herbs in the cloud forests of Monteverde, Costa Rica; the two taxa are probably congeneric (L. McDade, Duke Univ., pers. comm.), and we found naturally occurring hybrid populations at the study site. Both species grow in similar habitats and often grow in mixed stands at similar densities (see also Feinsinger et al., 1986). They have similar flower life spans (2-3 days), flowering seasons (Oct.-Apr.), ovules per flower (4), shapes and sizes of pollen grains (indistinguishable under light microscopy), seed dispersal (dry capsules which dehisce to release 1-4 similarly sized disc-shaped seeds), and general physiognomies. Neither species is apomictic. Both species can grow clonally. Based on growth of individual plants, interplant differences in flower color, and preliminary electrophoretic evidence of stems 3-8 m apart (N = 5 stems in Razisea and N = 3 stems in Hansteinia), individual clones appear to be mostly 15 m in diameter. They differ in the following features: mean corolla length (Razisea, 46 mm; Hansteinia, 22 mm) and pollen grains per flower (Razisea, 3,094.4 + 125.7, N = 11 flowers; Hansteinia, 5,696.3 + 306.3, N = 7). Control pollinations suggest that Razisea is more self-compatible than Hansteinia. In Razisea, 24/ 89 cross-pollinated flowers and 21/67 self-pollinated flowers developed into fruits; these proportions are not significantly different (2 x 2 contingency test, G = 0.14, P > 0.50). In Hansteinia the proportions were 29/83 for crossand 10/94 for self-pollinated flowers, a significant difference (G = 15.15, P < 0.001). Finally, the species differ in their pollinators. Hansteinia is pollinated primarily (85% of visits) by the hummingbird Lampornis calolaema; in this short-billed species, males are often territorial and females are generalist foragers (Feinsinger et al., 1986). Both sexes tend to feed at adjoining flowers in systematic fashion before moving to another patch (Stiles, 1985; Feinsinger et al., 1986). In contrast, Razisea is pollinated mostly (89% of visits) by the long-billed Phaethornis guy which shows no territoriality and feeds at a few flowers in a patch, even when many are available, before moving to another patch. Both our observations (Feinsinger et al., 1986) and those of Stiles (1981, 1985) indicate that Lampornis are relatively sedentary, whereas Phaethornis travel about a good deal, in classical traplining pollinator (Janzen, 1971) fashion. These differences in foraging behavior are expected to generate different mating patterns in the plant populations involved. Specifically, the effect of systematic foraging on flowers of adjacent individuals (nearestneighbor foraging) has been shown both experimentally and theoretically (Wright, 1951; Levin and Kerster, 1974; Turner et al., 1982; Handel, 1983a, 1983b; Wyatt, 1984) to produce significant inbreeding, homozygosity, and patchiness in plant populations, whereas long-distance foraging and resulting gene flow can be expected to produce greater levels of outcrossing in the populations concerned. For these reasons, we predicted that Hansteinia should show evidence of higher levels of inbreeding than Razisea. Because of the similarities noted above, Hansteinia and Razisea are very convenient for testing this prediction. The salient feature in which they differ is their corolla length and the associated pollinator. Consequently, any differences that may be detected in levels of inbreeding are most likely to reflect differences in gene flow resulting from behavior.