Individual Foraging Areas Research Articles

High foraging site fidelity and spatial segregation among individual great black‐backed gulls

Individual foraging site fidelity, whereby individuals repeatedly visit the same foraging areas, is widespread in nature, and likely benefits individuals through higher foraging efficiency and potentially, higher breeding success. It may arise as a consequence of habitat or resource specialisation, or alternatively, where resources are abundant or predictable, the partitioning of space might guarantee individuals exclusive foraging opportunities. We tracked seven adult great black‐backed gulls Larus marinus at a North Sea colony from early incubation to the end of the breeding season in 2016, providing a total of 1170 foraging trips over a mean ± SD tracking period of 67 ± 16 days. There was clear spatial segregation between individuals, with almost no overlap of their core areas (50% utilisation distribution) during incubation and chick‐rearing. Core areas were relatively small and there was high repeatability (R ± SE) in foraging parameters, including initial departure direction (0.73 ± 0.11), foraging range (0.41 ± 0.14) and cumulative distance travelled (0.19 ± 0.1) throughout the breeding season. Despite the low spatial overlap, there was little evidence of differential habitat use by individuals. The near‐exclusive individual foraging areas of this species, usually considered to be a generalist, indicate that where there is high resource availability throughout the breeding season and a small local population, individuals appear to adopt a territorial strategy which likely reduces intraspecific competition.

Influence of density-dependent competition on foraging and migratory behavior of a subtropical colonial seabird.

Density‐dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central‐place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while little is known about whether density‐dependent resource depletion influences individual migratory behavior outside the breeding season. Using breeding colony size as a surrogate for intraspecific resource competition, we tested for effects of colony size on breeding home range, nestling health, and migratory patterns of a nearshore colonial seabird, the brown pelican (Pelecanus occidentalis), originating from seven breeding colonies of varying sizes in the subtropical northern Gulf of Mexico. We found evidence for density‐dependent effects on foraging behavior during the breeding season, as individual foraging areas increased linearly with the number of breeding pairs per colony. Contrary to our predictions, however, nestlings from more numerous colonies with larger foraging ranges did not experience either decreased condition or increased stress. During nonbreeding, individuals from larger colonies were more likely to migrate, and traveled longer distances, than individuals from smaller colonies, indicating that the influence of density‐dependent effects on distribution persists into the nonbreeding period. We also found significant effects of individual physical condition, particularly body size, on migratory behavior, which in combination with colony size suggesting that dominant individuals remain closer to breeding sites during winter. We conclude that density‐dependent competition may be an important driver of both the extent of foraging ranges and the degree of migration exhibited by brown pelicans. However, the effects of density‐dependent competition on breeding success and population regulation remain uncertain in this system.

Intra- and Interspecific Variability of Echolocation Pulse Acoustics in the African Megadermatid Bats

The yellow-winged bat, Lavia frons, and the heart-nosed bat, Cardioderma cor, are sympatric species of the family Megadermatidae resident to East Africa. Cardioderma cor roost in groups and disperse to individual foraging areas at night, whereas L. frons roost in male-female pairs in Acacia trees within a foraging territory. Nightly foraging areas overlap across species, and thus interspecific differences in echolocation may reflect niche differences crucial for coexistence. Here we compare differences in echolocation from hand-released C. cor and L. frons, and L. frons individuals recorded during fly-bys. Furthermore, megadermatids display a host of social behaviors, including territoriality and singing, and thus intraspecific differences in echolocation may be important for facilitating behavior in this family but has not yet been assessed. We report the patterns of variability of echolocation by sex, body size, and individual of C. cor. We measured 354 pulses from 17 C. cor individuals and 35 pulses from four L. frons individuals in Tanzania. Up to four harmonics were observed in both C. cor and L. frons, with the second and third harmonics emphasized and the first suppressed. Cardioderma cor is a surface gleaner while L. frons is an aerial-hawker, and clear differences in frequency metrics (Fmin, Fmax, Fpeak) and duration reflect this. We measured 17 variables including temporal, frequency, and shape metrics for intraspecific C. cor pulse analyses. A MANOVA testing individuality on five principle components was significant, but performed poorly in a discriminant analysis. Body mass and forearm length did not correlate with any pulse metrics. Males had significantly lower Fmin and frequency contour parameters than females, although males were slightly smaller than females. These results suggest that L. frons and C. cor have clear interspecific differences in pulse acoustics that align with guild differences, and may serve heterospecific discrimination, while some intraspecific difference in C. cor, particularly by sex, are suggestive of other factors beyond navigation that influence pulse variability.

Large Home Range Size in the Ground Foraging Bat,Mystacina tuberculata, in Cold Temperate Rainforest, New Zealand

Large home range sizes are not unusual for small forest-dwelling bats living in cold temperate climates. However, lesser short-tailed bats (Mystacina tuberculata) feed on the ground for a proportion of their time, so their home range requirements may not conform to predictions based on other bat species. The home range size requirements of a population of M. tuberculata were investigated in cold temperate rainforest in the Eglinton Valley, Fiordland, New Zealand. Home range data was collected from a total of 21 out of 23 radio-tagged bats during late summer to early autumn of 1997 and 1998. Individual bats were followed for an average of 7.8 ± 3.2 (SD) days and collectively ranged over a total area of 14,710 ha. Thirteen colonial roosts were located within a central roosting area occupying 17 ha. A further 10 solitary roosts were located within individual foraging areas. Individual 100% minimum convex polygons varied considerably in size from 127.3 to 6,223.4 ha (median = 478.5 ha) with a range length of 2.2–23.0 km (median = 5.0 km). Cluster analyses revealed individual home ranges contained multi-nuclear patches of activity. Despite their large home ranges, bats concentrated activity (85%) in small core areas of 0.6–270.3 ha (median = 26.5 ha), with 85% of core areas less than 62 ha in size. Moderate levels of home range overlap amongst individuals (median = 26.8%) decreased to low levels for individual core areas (median = 3.7%). Our results show that M. tuberculata have relatively large home ranges, similar to many other small temperate rainforest bats, and implies that conservation areas designed for M. tuberculata should be large. Our predictions should be tested on populations of this species in areas with more abundant resources and milder climates.

Female Bechstein's Bats Share Foraging Sites with Maternal Kin but do not Forage Together with them – Results from a Long‐Term Study

AbstractIn many social animals, group members exchange information about where to feed. Thereby, they may gain direct benefits, for example, if social hunting enhances individual foraging success. Alternatively, individuals may receive indirect fitness benefits by preferentially sharing information about suitable feeding sites with kin. Indeed, in some species, a positive correlation between the degree of relatedness among individuals and the overlap among their foraging areas was found. However, sharing foraging sites with kin can also have costs if it increases food competition, which is not compensated by direct benefits. The goal of this study was to investigate whether sharing of individual foraging areas in female Bechstein's bats is best explained by kin selection or by direct benefits through social foraging. To assess their individual foraging behaviour, we analysed radio‐tracking data of 22 members of one maternity colony, including nine mother–daughter pairs, seven pairs of less closely related individuals and six pairs of unrelated bats. We examined the bats' fidelity to specific foraging areas during several years and quantified the influence of kinship on the overlap among individual foraging areas. By measuring how close to each other the bats foraged, we assessed whether individuals with overlapping areas are likely to forage together. Our study confirms previous findings that Bechstein's bats show high fidelity to foraging areas across years. Moreover, we found that relatives share foraging areas significantly more often compared with unrelated colony members. Finally, our data reveal for the first time that most colony members that share foraging areas are unlikely to forage together. This suggests that female Bechstein's bats gain no direct benefits from sharing foraging areas with members of the same maternal lineage. Our findings also have implications for conservation as habitat loss within a colony's home range might expose entire matrilines to high risks.

Satellite-tracking of female loggerhead turtles highlights fidelity behavior in northeastern Brazil

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 12:263-272 (2010) - DOI: https://doi.org/10.3354/esr00308 Satellite-tracking of female loggerhead turtles highlights fidelity behavior in northeastern Brazil Maria Ângela Marcovaldi1,*, Gustave G. Lopez1, Luciano S. Soares1, Eduardo H. S. M. Lima1, João C. A. Thomé2, Antonio P. Almeida2 1Fundação Pró-TAMAR, Caixa Postal 2219, 41950-970 Salvador, BA, Brazil 2Projeto TAMAR/ICMBio, Cx Postal 105, 29900-970 Linhares, ES, Brazil *Email: neca@tamar.org.br ABSTRACT: We studied inter- and postnesting movements in the major loggerhead Caretta caretta nesting population in Brazil. Ten breeding females were satellite-tracked from nesting grounds in the state of Bahia, northeastern Brazil, for up to 1284 d. Eight females stayed in the nesting area after deployment, showing fidelity between internesting home ranges and nesting locations, even at a local scale. During postnesting movements, all of the turtles migrated to the northern coast of Brazil to individual foraging areas on the continental shelf. Distances between nesting and foraging areas reached up to 2400 km, and migration lasted from 28 to 47 d. Five females were tracked during subsequent breeding migrations to the nesting area at different remigration intervals of 2 or 3 yr. Females were also tracked during a second postnesting migration back to foraging areas, and these showed strong fidelity to foraging grounds. Movements to and from foraging grounds occurred along the shelf, clearly delineating a migratory corridor. The northern coast of Brazil, specifically the coast of the state of Ceará, is an important foraging ground for loggerheads nesting along the northern coast of Bahia. KEY WORDS: Satellite-tracking · Caretta caretta · Internesting · Postnesting · Migration · Brazil Full text in pdf format PreviousCite this article as: Marcovaldi MÂ, Lopez GG, Soares LS, Lima EHSM, Thomé JCA, Almeida AP (2010) Satellite-tracking of female loggerhead turtles highlights fidelity behavior in northeastern Brazil. Endang Species Res 12:263-272. https://doi.org/10.3354/esr00308 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 12, No. 3. Online publication date: November 02, 2010 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2010 Inter-Research.

Roosting together, foraging apart: information transfer about food is unlikely to explain sociality in female Bechstein's bats ( Myotis bechsteinii )

To explain coloniality in birds and bats, communal roosts have been hypothesized to serve as information centers where colony members transfer knowledge about their habitat. If information is exchanged about food, individuals with low hunting success benefit by following successful foragers to their profitable feeding sites. Colony members should therefore forage together regularly and move in pairs or groups among different feeding places. In 1996 and 1997, we used radio-telemetry to study the nightly habitat use of ten adult female Bechstein's bats (Myotis bechsteinii) living in one maternity colony. Over several nights, each bat revisited its own foraging area, although females regularly switched day-roosts at the same time. Most individual foraging areas showed no, or only little, overlap with each other. Distances between individual activity centers were negatively and significantly correlated with the degree of individual day-roost association. Genetic similarity among colony members, determined using seven nuclear microsatellites, was significantly positively correlated with the degree of overlap among individual areas. Five females were repeatedly radio-tracked at different seasons, months apart. Even between years, all bats maintained their individual hunting areas. Because females are very loyal to their individual foraging areas and these areas are typically substantial distances from each other, information transfer about feeding sites is unlikely to be the crucial factor promoting coloniality. Therefore, other benefits of sociality like cooperative breeding may cause communal roosting. Strong fidelity to individual foraging areas suggests the importance of familiarity with the local habitat, and profound site knowledge could be a crucial "resource", promoting female philopatry in Bechstein's bats.

Three-dimensional space utilization by a marine predator

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 183:263-273 (1999) - doi:10.3354/meps183263 Three-dimensional space utilization by a marine predator David Grémillet1,*, Rory Paul Wilson1, Sandra Storch1, Yann Gary2 1Institut für Meereskunde Kiel, Abteilung Meereszoologie, Düsternbrooker Weg 20, D-24105 Kiel, Germany 2Groupe Ornithologique Normand, Université de Caen, F-14032 Caen Cedex, France *Present address: Institute of Terrestrial Ecology, Banchory Research Station, Hill of Brathens, Glassel, Banchory, Kincardineshire AB31 4BY, Scotland, UK E-mail: dgrem@wpo.nerc.ac.uk ABSTRACT: Diving seabirds should evolve a variety of foraging characteristics which enable them to minimize energy expenditure and to maximize net energy gain while searching for prey underwater. In order to assess the related ecological adaptations in a marine predator, we studied the at-sea distribution and the diving behaviour of 23 cormorants Phalacrocorax carbo (Linnaeus) breeding at the Chausey Islands (France) using VHF-telemetry and data loggers recording hydrostatic pressure. Birds foraged within an area of approximately 1131 km2 situated north-east of the breeding colony. This zone represents only 25% of the maximal potentially available area that the birds may utilize considering their maximum foraging range of 35 km. Individual birds remained within restricted individual foraging areas (on average 18 and 10% of the total utilized area in 1994 and 1995, respectively) throughout the study period. Moreover, the cormorants studied conducted an average of 42 dives per foraging trip, lasting for an average of 40 s (maximum 152 s), and reached an average maximum dive depth of 6.1 m (maximum 32 m) with median descent and ascent angles calculated to be 18.7° and 20.3°, respectively. Overall, 64% of all dives were U-shaped dives and 36% V-shaped dives. We use these results to demonstrate how both specialization and opportunism may support the remarkably high foraging efficiency of this marine predator. KEY WORDS: Phalacrocorax carbo · Diving behaviour · Foraging strategy · Specialization vs opportunism · Wildlife telemetry Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 183. Publication date: July 06, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Fluorescent powder as dye in bait for studying foraging areas in small mammals

Authors examined the characteristics of fluorescent powder as dye in bait for the purpose of studying individual foraging areas of the root vole Microtus oeconomus (Pallas, 1776). Colours were visible in the faeces 2-3 h after consumption, and were still evident 36-48 h after the removal of bait. It was possible to distinguish up to four different colours in faeces from one individual if the appropriate combination of coloured powder was used. The method is a better alternative to other markers commonly used in bait because only a small extra sampling effort is needed during trapping, and the observation of colours is relatively easy in UV-light. Because the persistance of the colour powder in the animal is relatively short, the method facilitates studies of short-term changes in foraging areas.

Genetic studies of the Hawksbill turtle Eretmochelys imbricata: evidence for multiple stocks in Australian waters

The hawksbill turtle, Eretmochelys imbricata, is endangered and currently declining in many parts of its global distribution. Efforts to manage the species are hampered by the lack of knowledge of the appropriate geographic units of management and the relationship among breeding populations and feeding assemblages. The Australian populations are among the few remaining large assemblages in the world, but may be under threat from harvesting in neighbouring countries. We use patterns of mitochondrial DNA variation to determine the geographic scale of breeding populations and to compare the genetic composition of turtles in feeding populations to those nesting at nearby major rookeries. Four of the major Australian rookeries were sampled, two on the western coast and two in northeastern Australia, as were turtles at two foraging sites. Significant differences in the frequency of two divergent mitochondrial DNA types separated the turtles nesting at major rookeries sampled on the northeastern versus western coasts of Australia, demonstrating that these populations are not connected by significant amounts of gene flow and should be considered as separate entities for management. There was no significant difference between the turtles nesting at two western rookeries 100 km apart, nor between those using the two northeastern rookeries separated by 750 km. This indicates that the size of the interbreeding unit for the hawksbill turtle is likely to be a region consisting of a group of islands rather than an individual island. Feeding populations were screened with a gene amplification test that discriminates between the two major DNA types. In each case, there was a significant difference in allele frequency between feeding populations and the nearest major rookery. This, together with previous reports of long distance migrations from tag returns, suggests that individual foraging areas support hawksbill turtles from distant breeding populations.

Foraging behaviour and echolocation in the rufous horseshoe bat (Rhinolophus rouxi) of Sri Lanka

In October 1984 foraging areas and foraging behaviour of the rufous horseshoe bat, Rhinolophus rouxi, were studied around a nursery colony on the hill slopes of Sri Lanka. The bats only foraged in dense forest and were not found in open woodlands (Fig. 1). This strongly supports the hypothesis that detection of fluttering prey is by pure tone echolocation within or close to echo-cluttering foliage. During a first activity period after sunset for about 30–60 min, the bats mainly caught insects on the wing. This was followed by a period of inactivity for another 60–120 min. Thereafter the bats resumed foraging throughout the night. They mainly alighted on specific twigs and foraged in flycatcher style. Individual bats maintained individual foraging areas of about 20x20 m. They stayed in this area throughout the night and returned to the same area on subsequent nights. Within this area the bats generally alighted on twigs at the same spots. Foraging areas were not defended against intruders. The bats echolocated throughout the night at an average repetition rate of 9.6±1.4 sounds/s. While hanging on twigs they scanned the surrounding area for flying prey by turning their bodies continuously around their legs. On average they performed one brief catching flight every 2 min and immediately returned to one of their favourite vantage points. Echolocation sounds may consist of up to three parts, a brief initial frequency-modulated (FM) component, a long constant frequency (CF) part lasting for about 40–50 ms, and a final FM part again (Fig. 4b, c). Adult males and females emitted pure tone frequencies in separate bands, the males from 73.5–77 kHz and the females from 76.5–79 kHz (Fig. 5). During scanning for prey from vantage points, the bats mostly emitted pure tones without any FM component (Fig. 4a). The last few pure tones emitted before take-off were prolonged to about 60 ms duration. The final FM part was therefore not an obligatory component of the echolocation signals in horseshoe bats. During flight and especially during emergence from the cave, most sounds consisted of a pure tone and loud initial and final FM sweeps. We therefore suggest that the initial FM part might also be relevant for echolocation. From our observations we conclude that the FM components are especially important during obstacle avoidance. In most sounds emitted in the field a fainter first harmonic was present. It was usually up to 30 dB fainter than the second harmonic, but in some instances it was as loud or even distinctly louder than the second one (Fig. 6a). Even within one sound the intensity relationship between the two harmonics may be reversed. We therefore suggest that the first harmonic is an integral part of the signal and relevant for information analysis in echolocation.