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1.
Trevor McIntyre Horst Bornemann Joachim Plötz Cheryl A. Tosh Marthán N. Bester 《Marine Biology》2011,158(9):2125-2139
The at-sea behaviour of marine top predators provides valuable insights into the distribution of prey species and strategies
used by predators to exploit patchily distributed resources. We describe the water column usage and dive strategies of female
southern elephant seals from Marion Island tracked between 2004 and 2008. Dives representing increases in forage effort were
identified using a method that combines dive type analyses and the calculation of relative amounts of time that animals spend
in the bottom phases of dives. Results from this analysis indicate that female elephant seals from Marion Island tend to display
lower levels of forage effort closer to the island and display intensive opportunistic forage bouts that occur at a minimum
distance of approximately 215 km from the island. Females from Marion Island dived deeper and for longer periods of time,
compared to females from other populations. Most animals displayed positive diel vertical migration, evidently foraging pelagically
on vertically migrating prey. A few animals displayed periods of reverse (negative) diel vertical migration, however, diving
to deeper depths at night, compared to daytime. This behaviour is difficult to explain and prey species targeted during such
periods unknown. Our results illustrate plasticity in foraging behaviour of southern elephant seals, as well as inter-population
differences in forage strategies. 相似文献
2.
Carey E. Kuhn 《Marine Biology》2011,158(3):649-663
In the heterogeneous marine environment, predators can increase foraging success by targeting physical oceanographic features,
which often aggregate prey. For northern fur seals (Callorhinus ursinus), two prevalent oceanographic features characterize foraging areas during summer in the Bering Sea: a stable thermocline
and a subsurface “cold pool”. The objective of this study was to examine the influence of these features on foraging behavior
by equipping fur seals from St. Paul Island (Alaska, USA) with time-depth recorders that also measured water temperature.
Foraging bout variables (e.g., mean dive depth and percent time diving in a bout) were compared with respect to subsurface
thermal characteristics (thermocline presence and strength and cold pool presence). Over 74% of bouts occurred in association
with strong thermoclines (temperature change > 5°C). Few differences were found for dive behavior in relation to the presence
of a thermocline and the cold pool, but for epipelagic bouts, a strong thermocline resulted in increased bottom times, number
of dive wiggles, and percent time diving when compared to moderate thermoclines. There was also a positive relationship between
mean dive depth and thermocline depth. The combination of increasing foraging effort in areas with strong thermoclines and
diving to depths closely related to the thermocline indicates this feature is important foraging habitat for northern fur
seals and may act to concentrate prey and increase foraging success. By recognizing the environmental features northern fur
seals use to find prey, managers will be better equipped to identify and protect foraging habitat that is important to northern
fur seals, and possibly other marine predators in the Bering Sea. 相似文献
3.
Penguins may exhibit plasticity in their diving and foraging behaviors in response to changes in prey availability. Chinstrap
penguins are dependent predators of Antarctic krill in the Scotia Sea region, but krill populations have fluctuated in recent
years. We examined the diet of chinstrap penguins at Livingston Island, South Shetland Islands, in relation to their diving
and foraging behavior using time-depth recorders over six breeding seasons: 2002–2007. When krill were smaller, more chinstrap
penguins consumed fish. In these years, chinstrap penguins often exhibited a shift to deep dives after sundown, and then resumed
a shallower pattern at sunrise. These night dives were unexpectedly deep (up to 110 m) and mean night dive depths sometimes
exceeded those from the daytime. The average size of krill in each year was negatively correlated to mean night dive depths
and the proportion of foraging trips taken overnight. Based on these patterns, we suggest that when krill were small, penguins
increasingly targeted myctophid fish. The average krill size was negatively correlated to the time chinstrap penguins spent
foraging which suggests that foraging on smaller krill and fish incurred a cost: more time was spent at sea foraging. 相似文献
4.
I. J. Staniland N. Gales N. L. Warren S. L. Robinson S. D. Goldsworthy R. M. Casper 《Marine Biology》2010,157(11):2383-2396
Foragers show adaptive responses to changes within their environment, and such behavioural plasticity can be a significant
driving force in speciation. We investigated how lactating Antarctic fur seals, Arctocephalus gazella, adapt their foraging within two contrasting ecosystems. Location and diving data were collected concurrently, between December
2003 and February 2004, from 43 seals at Bird Island, where krill, Euphausia superba, are the main prey, and 39 at Heard Island, where mostly fish are consumed. Seals at Heard Island were shorter and lighter
than those at Bird Island and they spent longer at sea, dived more frequently and spent more time in the bottom phase of dives.
Generalized additive mixed effects models showed that diving behaviours differed between the islands. Both populations exploited
diel vertically migrating prey species but, on average, Heard Island seals dived deeper and exceeded their estimated aerobic
dive limits. We propose that the recovery of the Heard Island population may be limited by the relative inaccessibility and
scarcity of food, whereas at Bird Island, the presence of abundant krill resources helps sustain extremely high numbers of
seals, even with increased intra- and inter-specific competition. Both populations of fur seals appear to be constrained by
their physiological limits, in terms of their optimal diving behaviour. However, there does appear to be some flexibility
in strategy at the level of trip with animals adjusting their time at sea and foraging effort, in order to maximize the rate
of delivery of energy to their pups. 相似文献
5.
Establishing where and when predators forage is essential to understanding trophic interactions, yet foraging behavior remains poorly understood in large marine carnivores. We investigated the factors leading to foraging success in gray seals (Halichoerus grypus) in the Northwest Atlantic in the first study to use simultaneous deployments of satellite transmitters, time depth recorders, and stomach-temperature loggers on a free-ranging marine mammal. Thirty-two seals were each fitted with the three types of instrumentation; however, complete records from all three instruments were obtained from only 13 individuals, underscoring the difficulty of such a multi-instrument approach. Our goal was to determine the characteristics of diving, habitat, and movement that predict feeding. We linked diving behavior to foraging success at two temporal scales: trips (days) and bouts (hours) to test models of optimal diving, which indicate that feeding can be predicted by time spent at the bottom of a dive. Using an information-theoretic approach, a Generalized Linear Mixed Model with trip duration and accumulated bottom time per day best explained the number of feeding events per trip, whereas the best predictor of the number of feeding events per bout was accumulated bottom time. We then tested whether characteristics of movement were predictive of feeding. Significant predictors of the number of feeding events per trip were angular variance (i.e., path tortuosity) and distance traveled per day. Finally, we integrated measures of diving, movement, and habitat at four temporal scales to determine overall predictors of feeding. At the 3-h scale, mean bottom time and distance traveled were the most important predictors of feeding frequency, whereas at the 6-h and 24-h time scales, distance traveled alone was most important. Bathymetry was the most significant predictor of feeding at the 12-h interval, with feeding more likely to occur at deeper depths. Our findings indicate that several factors predict feeding in gray seals, but predictor variables differ across temporal scales such that environmental variation becomes important at some scales and not others. Overall, our results illustrate the value of simultaneously recording and integrating multiple types of information to better understand the circumstances leading to foraging success. 相似文献
6.
We created a Bayesian hierarchical model (BHM) to investigate ecosystem relationships between the physical ecosystem (sea ice extent), a prey measure (krill density), predator behaviors (diving and foraging effort of female Antarctic fur seals, Arctocephalus gazella, with pups) and predator characteristics (mass of maternal fur seals and pups). We collected data on Antarctic fur seals from 1987/1988 to 1994/1995 at Seal Island, Antarctica. The BHM allowed us to link together predators and prey into a model that uses all the data efficiently and accounts for major sources of uncertainty. Based on the literature, we made hypotheses about the relationships in the model, which we compared with the model outcome after fitting the BHM. For each BHM parameter, we calculated the mean of the posterior density and the 95% credible interval. Our model confirmed others' findings that increased sea ice was related to increased krill density. Higher krill density led to reduced dive intensity of maternal fur seals, as measured by dive depth and duration, and to less time spent foraging by maternal fur seals. Heavier maternal fur seals and lower maternal foraging effort resulted in heavier pups at 22 d. No relationship was found between krill density and maternal mass, or between maternal mass and foraging effort on pup growth rates between 22 and 85 days of age. Maternal mass may have reflected environmental conditions prior to the pup provisioning season, rather than summer prey densities. Maternal mass and foraging effort were not related to pup growth rates between 22 and 85 d, possibly indicating that food was not limiting, food sources other than krill were being used, or differences occurred before pups reached age 22 d. 相似文献
7.
How energy costs affect foraging decisions is poorly understood for marine animals. To provide data relevant to this topic,
we examined the relationship between activity levels and foraging behavior by attaching activity recorders to 29 chick-rearing
wing-propelled diving birds (thick-billed murres, Uria lomvia) in 1999–2000. We connected the activity during the final dive bout with the prey item we observed being fed to the chicks.
After accounting for changes in activity level with depth, activity was highest during the final dive of a dive bout, reflecting
maneuvring during prey capture. Pelagic prey items, especially invertebrates (amphipods), were associated with higher depth-corrected
activity, leading to shorter dives for a given depth (presumably due to higher oxygen consumption rates) and, thus, shorter
search times (lower bottom time for a given depth). Pelagic prey items were likely captured during active pursuit, with the
birds actively seeking and pursuing schooling mid-water prey. In contrast, benthic prey involved low activity and extended
search times, suggesting that the birds slowly glided along the bottom in search for prey hidden in the sediments or rocks.
We concluded that activity levels are important in determining the foraging tactics of marine predators.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
André Chiaradia Yan Ropert-Coudert Akiko Kato Thomas Mattern Julija Yorke 《Marine Biology》2007,151(4):1535-1542
Little Penguins, Eudyptula minor, breed in several small colonies in New Zealand and Australia. In this study, we compare the birds’ diving performances at
different sites situated throughout their breeding range. Environmental conditions and breeding success vary drastically amongst
colonies, but all birds feed on similar types of prey and face similar limitations on their foraging range. We examined several
diving parameters and calculated the proportion of foraging zone available during breeding to examine whether oceanographic
and geographic factors in the foraging zone can explain variations in diving behaviour and fledging success among the different
colonies. In colonies with high fledging success, Penguin Island and Oamaru, penguins made shallow dives <50 m depth and had
lower diving effort. More than 90% of the foraging zone was in waters <50 m depth in these colonies. Motuara Island also has
shallow waters with 95% <50 m depth, but the fledging success was low. Phillip Island has only 42% of waters <50 m and comparatively
low fledging success. Thus, penguins dived deeper and showed a higher diving effort in colonies with lower fledging success
(Motuara Island and Phillip Island), indicating that they were disadvantaged compared to conspecifics from other colonies
that dived shallower and with a lesser diving effort. We concluded that bathymetry is an important factor, but not the only
one, which influences fledging success. 相似文献
9.
April Hedd P. M. Regular W. A. Montevecchi A. D. Buren C. M. Burke D. A. Fifield 《Marine Biology》2009,156(4):741-751
Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging
options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit
flexible foraging tactics. Here we document the behavioral flexibility of pursuit-diving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day
and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (≥50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water
in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the
day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column.
Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures
limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time
needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty
of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of dives per bout) reflects
both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential
to escape from avian predators could increase. 相似文献
10.
Sebastián P. Luque John P. Y. Arnould Edward H. Miller Yves Cherel Christophe Guinet 《Marine Biology》2007,152(1):213-224
The duration of periods spent ashore versus foraging at sea, diving behaviour, and diet of lactating female Antarctic (Arctocephalus gazella, AFS) and subantarctic (A. tropicalis, SFS) fur seals were compared at Iles Crozet, where both species coexist. The large disparity in lactation duration (SFS:
10 months, AFS: 4 months), even under local sympatry, has led to the expectation that AFS should exhibit higher foraging effort
or efficiency per unit time than SFS to allow them to wean their pups in a shorter period of time. Previous evidence, however,
has not supported these expectations. In this study, the distribution of foraging trip durations revealed two types of trips:
overnight (OFT, <1 day) and long (LFT, >1 day), in common with other results from Macquarie Island. However, diving behaviour
differed significantly between foraging trip types, with greater diving effort in OFTs than in LFTs, and diving behaviour
differed between fur seal species. OFTs were more frequent in SFS (48%) than in AFS (28%). SFS performed longer LFTs and maternal
attendances than AFS, but spent a smaller proportion of their foraging cycle at sea (66.2 vs. 77.5%, respectively). SFS dove
deeper and for longer periods than AFS, in both OFTs and LFTs, although indices of diving effort were similar between species.
Diel variation in diving behaviour was lower among SFS, which foraged at greater depths during most of the night time available
than AFS. The diving behaviour of AFS suggests they followed the nychthemeral migration of their prey more closely. Concomitant
with the differences in diving behaviour, AFS and SFS fed on the same prey species, but in different proportions of three
myctophid fish (Gymnoscopelus fraseri, G. piabilis, and G. nicholsi) that represented most of their diet. The estimated size of the most important fish consumed did not vary significantly between
fur seal species, suggesting that the difference in dive depth was mostly a result of changes in the relative abundance of
these myctophids. The energy content of these fish at Iles Crozet may thus influence the amount and quality of milk delivered
to pups of each fur seal species. These results contrast with those found at other sites where both species coexist, and revealed
a scale of variation in foraging behaviour which did not affect their effort while at sea, but that may be a major determinant
of foraging efficiency and, consequently, maternal investment. 相似文献
11.
Sixty-eight yellowfin tuna, Thunnus albacares, (60-135 cm fork length) were caught and released with implanted archival tags offshore off Baja California, Mexico, during
October 2002 and October 2003. Thirty-six fish (53%) were recaptured and the data were downloaded from all 36 recovered tags.
Time at liberty ranged from 9 to 1,161 days, and the data were analyzed for the 20 fish that were at liberty for 154 or more
days. The accuracy in the position estimates, derived from light-level longitude data and sea-surface temperatures (SSTs)
based latitude, is about 0.41° in longitude and 0.82° in latitude, in this region. The movement paths, derived from position
estimates, for the 20 yellowfin indicated that 19 (95%) remained within 1,445 km of their release locations. The estimated
mean velocity along movement paths was 77 km/day. The southern and northern seasonal movement paths observed for yellowfin
off Baja California are influenced by the seasonal movements of the 18°C SST isotherm. Cyclical movements to and from suitable
spawning habitat (≥24°C SST) was observed only for mature fish. For the 12 fish that demonstrated site fidelity, the mean
95 and 50% utilization distributions were 258,730 km2 and 41,260 km2, respectively. Evaluations of the timed depth records resulted in discrimination of four distinct behaviors. When exhibiting
type-1 diving behavior (78.1% of all days at liberty) the fish remained at depths less than 50 m at night and did not dive
to depths greater than about 100 m during the day. Type-2 diving behavior (21.2% of all days at liberty) was characterized
by ten or more dives in excess of 150 m during the day. Type-2 diving behavior is apparently a foraging strategy for fish
targeting prey organisms of the deep-scattering layer during the day, following nighttime foraging within the mixed layer
on the same prey. Yellowfin tuna exhibited occasional deep-diving behavior, and some dives exceeded 1,000 m, where ambient
temperatures were less than 5°C. Surface-oriented behavior, defined as the time fish remained at depths less than 10 m for
more than 10 min, were evaluated. The mean number and duration of surface-oriented events per day for all fish was 14.3 and
28.5 min, respectively. Habitat utilization of yellowfin, presented as monthly composite horizontal and vertical distributions,
indicates confined geographical distributions, apparently resulting from an affinity to an area of high prey availability.
The vertical distributions indicate greater daytime depths in relation to a seasonally deeper mixed layer and a greater proportion
of daytime at shallower depths in relation to a seasonally shallower mixed layer. 相似文献
12.
In situ measures of foraging success and prey encounter reveal marine habitat-dependent search strategies 总被引:1,自引:0,他引:1
Predators are thought to reduce travel speed and increase turning rate in areas where resources are relatively more abundant, a behavior termed "area-restricted search." However, evidence for this is rare, and few empirical data exist for large predators. Animals exhibiting foraging site fidelity could also be spatially aware of suitable feeding areas based on prior experience; changes in movement patterns might therefore arise from the anticipation of higher prey density. We tested the hypothesis that regions of area-restricted search were associated with a higher number of daily speed spikes (a proxy for potential prey encounter rate) and foraging success in southern elephant seals (Mirounga leonina), a species exhibiting both area-restricted searches and high interannual foraging site fidelity. We used onshore morphological measurements and diving data from archival tags deployed during winter foraging trips. Foraging success was inferred from in situ changes in relative lipid content derived from measured changes in buoyancy, and first-passage time analysis was used to identify area-restricted search behavior. Seals exhibited relatively direct southerly movement on average, with intensive search behavior predominantly located at the distal end of tracks. The probability of being in search mode was positively related to changes in relative lipid content; thus, intensively searched areas were associated with the highest foraging success. However, there was high foraging success during the outward transit even though seals moved through quickly without slowing down and increasing turning rate to exploit these areas. In addition, the probability of being in search mode was negatively related to the number of daily speed spikes. These results suggest that movement patterns represent a response to prior expectation of the location of predictable and profitable resources. Shelf habitat was 4-9 times more profitable than the other habitats, emphasizing the importance of the East Antarctic shelf for this and other predators in the region. We have provided rare empirical data with which to investigate the relationship between predator foraging strategy and prey encounter/ foraging success, underlining the importance of inferring the timing and spatial arrangement of successful food acquisition for interpreting foraging strategies correctly. 相似文献
14.
To exploit resources in their environment, odontocete cetaceans have evolved sophisticated diving abilities to allow effective
foraging. However, data on the diving behaviour and underwater foraging behaviour remains limited. This study made use of
echolocation clicks and other calls to study the diving behaviour of bottlenose dolphins. Dolphins used the full water column
and consistently dived to depths of around 50 m, close to the seabed. However, the majority of their time appeared to be spent
within the surface layers of the water column. In addition, by localising calls that have been associated with prey capture
events (Janik, Proc R Soc Lond Ser B 267:923–927, 2000a), it appeared that certain forms of feeding behaviour occurred primarily
at depths of between 20 and 30 m. Furthermore, data on the depth of clicks made before and after these feeding calls suggested
that during the minute before the calls, dolphins were consistently diving from the surface to depths close to the seabed,
and were subsequently returning to the surface after the calls. This passive acoustic technique proved an accurate method
for studying the depth distribution of dolphin vocalisations. By exploiting the natural sounds made by these wild odontocetes,
this investigation provided a previously unavailable perspective on the the 3D nature of bottlenose dolphins foraging behaviour.
It confirmed that while the dolphins spent the majority of time close to the surface, the full water column was exploited
during foraging events. 相似文献
15.
Iain C. Field Corey J. A. Bradshaw John van den Hoff Harry R. Burton Mark A. Hindell 《Marine Biology》2007,150(6):1441-1452
Southern elephant seals are important apex predators in a highly variable and unpredictable marine environment. In the presence
of resource limitation, foraging behaviours evolve to reduce intra-specific competition increasing a species’ overall probability
of successful foraging. We examined the diet of 141 (aged 1–3 years) juvenile southern elephant seals to test the hypotheses
that differences between ages, sexes and seasons in diet structure occur. We described prey species composition for common
squid and fish species and the mean size of cephalopod prey items for these age groups. Three cephalopod species dominated
the stomach samples, Alluroteuthis antarcticus, Histioteuthis eltaninae and Slosarczykovia circumantarcticus. We found age-related differences in both species composition and size of larger prey species that probably relate to ontogenetic
changes in diving ability and haul-out behaviour and prey availability. These changes in foraging behaviour and diet are hypothesised
to reduce intra-specific food competition concomitant with the increase in foraging niche of growing juveniles. 相似文献
16.
The fine link between a particular dive pattern and a specific prey item represents a challenging task in the analysis of
marine predator–prey relationships. There is growing evidence that prey type affects diving seabirds’ foraging strategies,
dive shapes and underwater activity costs. This study investigates whether a generalist diver, the Great Cormorant Phalacrocorax carbo, modifies the time budget allocated to prey-capture behaviour and breathing strategies (reactive vs. anticipatory) with respect
to the prey type (pelagic vs. benthic). Video recordings of 91 Great Cormorants show how the ecology and behaviour of their
main prey, Mullets (Mugilidae) and Flounders Platichthys flesus, affect dive/surface durations and the diving pattern. The demersal habit and the low mobility of Flounders leads to an easy
access to prey with an anticipatory strategy. Moreover, the patchy distribution of this fish species increases prey-capture
rates. Conversely, Mullets exploit the whole water column and are highly mobile, and this is reflected in the need of performing
two sequential dives to capture a prey, both longer and likely more expensive, with a consequent switch of strategy from reactive
in the searching phase to anticipatory breathing during prey-capture events. This study provides evidence that a generalist
diver may switch between different foraging strategies, and it shows how each of them may be optimal under particular ecological
conditions. These constraints influence the dynamics that operate within the marine food chains and have relevant implications
in managing lagoon areas, including fish ponds. 相似文献
17.
Contrasting conditions at-sea are likely to affect the foraging behaviour of seabirds. However, the effect of season on the dive parameters of penguins is poorly known. We report here on an extensive study of the diving behaviour of king penguins (Aptenodytes patagonicus) over the bird's complete annual cycle at the Crozet Islands. Time-depth recorders were used to record dive duration, bottom duration, post-dive interval, ascent rate and descent rate in breeding adults during different seasons in 1995 and 1996. Seasons included summer (n=6, incubation; n=6, chick brooding), autumn and winter (n=5 and n=3, respectively, chick at the crèche stage), and spring (n=4, birds at the post-moult stage). In all seasons dive duration increased with dive depth, but, for a given depth, dives were longer in winter (6.8 min when averaged over the 100-210 m depth layer) than in spring (4.6 min) and summer (4.4 min). The time spent at the bottom of the dives, which probably represents a substantial part of the feeding time, was much longer in winter (2.5 min per dive for dives over the 100-210 m layer) than during other seasons (1.0-1.4 min), i.e. there was a 2.5-fold augmentation for similar diving depths. Ascent and descent rates increased with increasing dive depth, but no difference in the relationships between rates of ascent and descent and dive depth was found among seasons. Furthermore, for all dive depths, ascent and descent rates were independent of the bottom duration. In all seasons post-dive intervals increased with dive duration and with dive depth, but they were longer in spring (2.3 min for dives over the 100-210 m layer) and summer than in autumn and winter (1.6-1.8 min). The diving efficiency decreased with increasing dive depth and was higher in autumn and winter (0.22-0.29) than in summer and spring (0.15-0.18). The large increase in bottom and dive duration from spring to winter is in agreement with the seasonal drop in prey density, with penguins spending more time searching for prey. In contrast, the consistency of the vertical velocity during contrasting conditions at-sea suggests that the transit time to depth is an important component of the foraging behaviour (scanning of the water column) that is independent of the prey availability. The time budget of the penguins during diving in a fluctuating environment appears to vary primarily during the bottom phase of the dives, with bottom duration increasing with diminishing prey supplies, while post-dive intervals shorten in the same time. 相似文献
18.
Klemens Pütz Andrea Raya Rey Nic Huin Adrian Schiavini Andrea Pütz Bernhard H. Lüthi 《Marine Biology》2006,149(2):125-137
The diving behaviour of southern rockhopper penguins (Eudyptes c. chrysocome) was studied at two breeding sites in the Southwest Atlantic: the Falkland Islands and Staten Island, Argentina. Incubating and brooding birds were equipped with time-depth recorders to monitor their foraging activities. Rockhopper penguins from Staten Island started their breeding season about 3 weeks earlier than their conspecifics from the Falkland Islands. The foraging area used by incubating males from the Falkland Islands comprised about 150,000 km² to the northeast of the breeding site and was characterised by shelf and slope waters, whereas the foraging area of incubating males from Staten Island comprised 350,000 km² of oceanic waters to the southeast of the breeding site. A number of dive parameters were measured and compared between the four study groups: Incubating males and brooding females from the Falkland Islands, and incubating males and females from Staten Island. In all study groups, dive depth correlated positively to light intensity, dive duration and vertical velocity. However, significant differences between various diving parameters of the study groups were noted, not only in terms of diving performance, but also as regards diving efficiency (DE). A principal component analysis (PCA) on 16 variables revealed that 75% of the variance could be explained by only two principal components: diving pattern (PC1) and diving effort (PC2). PC1 indicated that the birds from Staten Island, both males and females, dived deeper, covered a greater vertical distance per hour and had higher ascent rates, but spent less time underwater and at the bottom of a dive, and had a lower DE than conspecifics from the Falkland Islands. PC2, which included the percentage of foraging dives, the number of dives per hour, dive duration, bottom time and descent rate, differed significantly between incubating males from the Falkland Islands and the other three groups, which were all very similar. Overall, the diving behaviour was notably similar to that of conspecifics from the Indian and Pacific Oceans. The implications of the results in terms of intra-specific adaptations as well as potential threats from human activities are discussed. 相似文献
19.
From the 1980s, Mediterranean shags Phalacrocorax aristotelis desmarestii have become regular summer visitors in the Gulf of Trieste (N-E Italy), as post-breeding movements from Croatian breeding
colonies. To characterize such a recent habit and to explore diving optimality models, we investigate foraging strategies
and diving patterns at different depths, during breeding and post-breeding seasons. Behavioural data were cross-checked with
the species’ diet. Shags foraged on and close to the sea bed, with a prevalent anticipatory breathing strategy. In the Gulf
of Trieste, the shallow depths and low mobility of prey allowed shags to use just the oxygen of the respiratory tract, reducing
the physiological stress for diving. In Croatia, dive costs increased with depth and prey mobility, resulting in a higher
oxygen expenditure that involved also respiratory stores. Such ecological and physiological aspects characterize the Gulf
of Trieste as an optimal area for feeding and restoring from the costs of breeding season incurred in Croatia and could be
the basis of these post-breeding movements. 相似文献
20.
Olivia Lee Russel D. Andrews Vladimir N. Burkanov Randall W. Davis 《Marine Biology》2014,161(5):1165-1178
The ontogeny of diving and foraging behavior of northern fur seal pups from a stable population on Bering Island, Russia, was recorded with animal-borne instruments during their first few months at sea, a critical period during their first year at sea. Thirty-five pups were instrumented with satellite-linked time-depth recorders and stomach temperature pills. Diving occurred predominantly at night with deeper and longer dives as the pups matured. Mean dive depths were correlated with lunar illumination, whereas mean dive durations were also correlated with time of day and sex. Foraging success did not differ between sexes, and there was no relationship between meal size (as indicated by feeding event duration and minimum stomach temperature) and lunar illumination fraction or maximum foraging depth. Although most pups were able to successfully forage within 3 days of starting their migration, the number of feeding events recorded each day remained low (mean 1.6 events day?1). There was no indication of an appreciable increase in meal size after the first 2 weeks of the migration despite an increase in dive frequency and depth. The results are consistent with observations that pups do not gain mass during their first year and emphasize the risk of starvation from infrequent foraging in cold water. 相似文献