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1.
Alice H. Tait David Raubenheimer Karen A. Stockin Monika Merriman Gabriel E. Machovsky-Capuska 《Marine Biology》2014,161(12):2791-2801
Foraging theory proposes that the nutritional driver of food choice and foraging in carnivores is energy gain. In contrast, recent laboratory experiments have shown that several species of carnivore select prey that provides a diet with a specific balance of macronutrients, rather than the highest energy content. It remains, however, to be determined how nutritionally variable the foods of predators in the wild are, and whether they feed selectively from available prey to balance their diet. Here, we used a geometric method named the right-angled mixture triangle (RMT) for examining nutritional variability in the prey and selected diets of a group of wild carnivores and marine top predators, the gannets (Morus spp.). A prey-level diet analysis was performed on Australasian gannets (M. serrator) from two New Zealand locations, and the macronutrient composition of their chosen prey species was measured. We use RMT to extend the comparison in the compositions of foods and diets from Australasian gannets from Australia as well as Northern gannets (M. bassanus) and Cape gannets (M. capensis). We found nutritional variability at multiple scales: intra- and interspecific variability in the pelagic fish and squid prey themselves; and intra- and interspecific variability in the diets consumed by geographically disparate populations of gannets. This nutritional variability potentially presents these predatory seabirds with both opportunity to select an optimal diet, and constraint if prevented from securing an optimal diet. 相似文献
2.
Emeline Pettex Svein-H?kon Lorentsen David Grémillet Olivier Gimenez Robert T. Barrett Jean-Baptiste Pons Céline Le Bohec Francesco Bonadonna 《Marine Biology》2012,159(12):2743-2756
The survival of marine predators depends on behavioural plasticity to cope with changes in prey distribution. Variability in behaviour might predict plasticity and is easier to assess than plasticity. Using miniaturized GPS loggers over several breeding seasons in two Norwegian Northern gannet (Morus bassanus) colonies, we investigated if and how the variability within and between individuals, but also between colonies and years, affected foraging strategies. Results revealed strong individual variability (foraging trip durations, foraging effort and different foraging areas). Individuals from both colonies showed preferred commuting routes, flight bearings and feeding hotspots. Individuals from the largest colony used larger and more foraging areas than individuals from the small colony. Feeding hotspots and foraging ranges varied amongst years in the largest colony only. Our study demonstrated that gannets show flexibility by changing prey fields that are driven by shifting oceanographic conditions. 相似文献
3.
Stefan Garthe William A. Montevecchi Gilles Chapdelaine Jean-Francois Rail April Hedd 《Marine Biology》2007,151(2):687-694
In order to forage and to provision offspring effectively, seabirds negotiate a complex of behavioural, energetic, environmental
and social constraints. In first tests of GPS loggers with seabirds in North America, we investigated the foraging tactics
of free-ranging northern gannets (Sula bassana) at a large and a medium-sized colony that differed in oceanography, coastal position and prey fields. Gannets at Low Arctic
colony (Funk Island) 50 km off the northeast coast of Newfoundland, Canada provisioned chicks almost entirely with small forage
fish (capelin Mallotus villosus, 89%), while at boreal colony (Bonaventure Island) 3 km from shore in the Gulf of St. Lawrence, Quebec, Canada, large pelagic
fish dominated parental prey loads (Atlantic mackerel Scomber scombrus 50%, Atlantic herring Clupea harengus 33%). Mean foraging range and the total distance travelled per foraging trip were significantly greater at the larger inshore
colony (Bonaventure) than at the smaller offshore colony (Funk Island; 138 and 452 km vs. 64 and 196 km, respectively). Gannets
from Funk Island consistently travelled inshore to forage on reproductive capelin shoals near the coast, whereas foraging
flights of birds from Bonaventure were much more variable in direction and destination. Birds from the Low Arctic colony foraged
in colder sea surface water than did birds from the boreal colony, and dive characteristics differed between colonies, which
is concordent with the difference in prey base. Differences between the colonies reflect oceanographic and colony-size influences
on prey fields that shape individual foraging tactics and in turn generate higher level colony-specific foraging “strategies”. 相似文献
4.
Isabel Afán Joan Navarro Laura Cardador Francisco Ramírez Akiko Kato Beneharo Rodríguez Yan Ropert-Coudert Manuela G. Forero 《Marine Biology》2014,161(3):657-668
As central-place foragers, pelagic seabirds are constrained by spatiotemporal heterogeneity to find productive marine areas and compete for prey. We analysed 97 foraging trips to study the movement and oceanographic characteristics of foraging habitats of two different—yet closely related—species of shearwaters (Scopoli’s shearwater Calonectris diomedea and Cory’s shearwater C. borealis) breeding in sympatry in the Mediterranean. We combined various methodological approaches (GPS-tracking, species distribution modelling and stable isotope analysis) to explore the foraging strategies of these two species. Isotopic results suggested that trophic habits of both shearwater species were similar, mainly based on pelagic fish consumption. Foraging areas of both species were characterized by shallow waters near the colony. Both shearwater species exploited persistent productive marine areas. The foraging areas of the two species broadly overlapped during the incubation period, but during chick-rearing period, Scopoli’s shearwaters apparently foraged in different areas than Cory’s shearwaters. 相似文献
5.
The diet of the Humboldt penguin (Spheniscus humboldti) was examined and compared in two colonies in Chile. Field work was conducted on Pan de Azúcar Island in northern Chile in the breeding season 1998/1999 and on the Puñihuil Islands in southern Chile over two successive breeding seasons during 1997/1998 and 1998/1999. Penguin diet was studied by stomach-pumping birds and analysed by species composition, size and mass of prey. Fish were the dominant prey item at both sites, the contribution of cephalopods and crustaceans varying between sites. The fish prey consisted predominantly of school fish, but there were clear latitudinal differences in fish prey taken. Penguins in the northern colony consumed primarily garfish (Scomberesox saurus), while birds at the southern colony of Puñihuil fed primarily on anchovy (Engraulis ringens), Araucanian herring (Strangomera bentincki) and silverside (Odontesthes regia). The results showed significant differences in terms of numbers of fish taken between the two breeding seasons at Puñihuil. In 1997/1998 penguins consumed almost exclusively anchovy, while they fed primarily on silversides in the successive year. Almost all prey, except stomatopods, were characterised as being pelagic species that occur in relatively inshore water, consistent with the foraging behaviour of Humboldt penguins. The dependence of Humboldt penguins on commercially exploited, schooling prey species makes the species particularly susceptible to changes in prey stocks, due to non-sustainable fisheries management.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
6.
Vitor H. Paiva Pedro Geraldes Iván Ramírez Ana Meirinho Stefan Garthe Jaime A. Ramos 《Marine Biology》2010,157(6):1385-1399
Many breeding seabird species are central-place foragers and constrained to find productive prey patches within their foraging
ranges. We assessed how different populations of a pelagic seabird species, the Cory’s shearwater Calonectris diomedea, breeding in oceanic and neritic conditions, cope with these constraints in the North Atlantic, during both incubation and
chick-rearing periods. We analysed 237 foraging trips to study the movements and oceanographic characteristics of foraging
habitats of seven different populations of Cory’s shearwaters. Generally, oceanic populations exhibited higher foraging effort,
by travelling more time and to more distant areas, and larger home ranges and feeding areas, than the neritic population (i.e.
breeding on an island within the Portuguese continental platform). On their short trips (i.e. ≤4 days), birds from the different
populations fed mostly in shallower waters around the colony. During long trips (i.e. ≥5 days), feeding areas of both oceanic
and neritic populations were characterized by high concentration values of chlorophyll-a, low sea-surface temperature and shallower habitats, with oceanic populations of the Azores exploiting areas north of the
islands over known seamounts and frontal regions. Birds from other oceanic population (Selvagens) also exploited the African
continental shelf system on their long trips. The home ranges of the different populations overlapped widely, but there was
a general spatial segregation in terms of the core feeding areas at the population level. Core feeding areas and areas of
foraging overlap between different populations should be important to inform conservation management measures, such as the
definition of Marine Important Bird Areas for seabirds over the North Atlantic. 相似文献
7.
Patterns of space use provide key insights into how animals exploit local resources and are linked to both the fitness and
distribution of individuals. We studied territory size, mobility, and foraging behavior of young-of-the-year Atlantic salmon
Salmo salar in relation to several key environmental factors in Catamaran Brook, New Brunswick, Canada. The 50 study fish were all multiple
central-place foragers (i.e., alternated among several sit-and-wait foraging stations) and showed great variability in territory
size and the total distance traveled within the territories. Territory size increased with the mean distance traveled between
consecutive foraging stations, the number of stations visited, and the mean foraging radius. Fish also varied greatly in how
much of the total travel distance was associated with foraging at a station (14.8–91.8%) versus switching among stations (4.6–84.3%).
As predicted, fish in slow-flowing waters, where drifting prey were scarce, used larger multiple central-place territories
than individuals in faster, more productive waters. Interestingly, however, the most mobile fish did not inhabit slow-running
waters as predicted but were found at intermediate (optimal) water current velocities. Hence, our study suggests that among
some multiple central-place foragers, increased mobility may not only serve to increase prey encounter rate but may reflect
an attempt to patrol territories in favorable habitats. Further studies are needed to determine the generality and the ultimate
benefits of multiple central-place space use among stream-dwelling fish and other animals. 相似文献
8.
Adjustment of parental effort to manipulated foraging ability in a pelagic seabird,the thin-billed prion Pachyptila belcheri 总被引:6,自引:0,他引:6
Henri Weimerskirch Olivier Chastel Luc Ackermann 《Behavioral ecology and sociobiology》1995,36(1):11-16
An experiment was designed to examine in a long-lived seabird, the thin-billed prion (Pachyptila belcheri), how adults adjust their food provisioning strategy when their foraging abilities are reduced and when the chick's needs are increased. To reduce the foraging abilities of adults we impaired their flying ability by removing some flight feathers (handicapped), and to increase the food needs of the chick one parent was retained (single). Birds made either short foraging trips lasting 1–3 days, or long trips lasting 5–9 days. Control birds alternated long and short trips whereas single birds or handicapped birds made several successive short trips and thereafter a long trip. In each treatment, food loads tended to be heavier after long trips than after short trips, and single birds tended to bring heavier loads than control or handicapped birds. Birds in the three treatments lost similar amounts of mass after short trips and gained similar amounts of mass after long trips. However, the mass of handicapped birds declined through the experiment, while that of control and single birds remained stable. Although the proportion of chicks that died during the experiment was similar among the three treatments, the chicks fledged by a single bird were lighter than those in control nests. The results of the experiment suggest that thin-billed prions adjust their breeding effort differently to decreased flying ability or increased food demand by the chick. Single birds increase foraging effort without allowing their condition to deteriorate. Conversely, handicapped birds are unable to maintain their body condition while sustaining the chick at the same rate as control birds. It is suggested that in this long-lived seabird, adults probably adjust their breeding effort so that they do not incur the risk of an increased mortality, this risk being monitored by the body condition. 相似文献
9.
Joan Navarro Maite Louzao José Manuel Igual Daniel Oro Antonio Delgado José Manuel Arcos Meritxell Genovart Keith A. Hobson Manuela G. Forero 《Marine Biology》2009,156(12):2571-2578
Pelagic seabirds obtain food from oceans where the availability of their prey changes rapidly both seasonally and spatially.
Here, we investigated changes in the trophic habits of the critically endangered Balearic shearwater (Puffinus mauretanicus) through the breeding season and tested for dietary differences between sexes and age classes. We analysed δ15N and δ13C values in blood of adults during the pre-incubation, incubation and chick-rearing periods and of their chicks. Using a two-isotope
mixing model, we estimated dietary contributions based on isotope values from potential prey species which included small
pelagic species available naturally and demersal fish species available only from trawling discards. Balearic shearwaters
showed clear isotopic and dietary variation through the breeding season. During pre-incubation, breeding adults appeared to
exploit demersal fish, whereas during the incubation and chick-rearing period, they fed mainly on pelagic anchovies (Engraulis encrasicolus) and pilchards (Sardina pilchardus). Similarly, chicks were fed mainly with anchovies, a resource with a high energetic value. This variation in the dietary
habits of adult shearwaters during the breeding season was probably related to both natural and fishery-induced seasonal changes
in the availability of potential prey species within their main feeding grounds. However, changes in the nutritional requirements
of the shearwaters could also play an important role. Indeed, diet differed between sexes during pre-incubation: females fed
less on trawling discards and more on small pelagic fish than males. This sexual segregation in diet could be the consequence
of higher nutritional requirements of females during this period. Our study reveals the differential importance of both trawling
discards and small pelagic fish species for a pelagic seabird depending on the breeding period and illustrates the importance
of considering the entire breeding season when making inferences about the importance of specific prey in seabird dietary
studies. 相似文献
10.
There is little information on the effort put into foraging by seabirds, even though it is fundamental to many issues in behavioural ecology. Recent researchers have used changes in the underwater cruising speed of penguins to allude to prey ingestion since accelerations are thought to reflect the encounter and pursuit of prey. In this study, we attached minute accelerometers, to determine flipper beat frequency as a proxy for prey pursuit, to Little Penguins Eudyptula minor foraging in shallow waters in Western Australia. During diving, Little Penguins flapped continuously and at a regular pace of 3.16 Hz while descending the water column and throughout the bottom phase of most dives. However, the frequency and amplitude of wingbeats increased transitorily, reaching 3.5–5.5 Hz, during some dives indicating prey pursuit. Pursuit phases lasted a mean of 2.9±3.3 s and occurred principally during the bottom phases of dives (75.4%). Most dives in all birds (86%) had a clear square-shaped depth profile indicating feeding activity near the seabed in the shallow waters of the bays. Hourly maximum depth, time spent underwater, percentage of dives with pursuit events and catch per unit effort showed an overall increase from zero at ca. 0500 h to a maximum during the hours around mid-day before decreasing to zero by 1900 h. During pursuit phases, Little Penguins headed predominantly downward, probably using the seabed to assist them in trapping their prey. In the light of our results, we discuss depth use by Little Penguins and their allocation of foraging effort and prey capture success as a function of environmental conditions. 相似文献
11.
Kyle Hamish Elliott Roger D. Bull Anthony J. Gaston Gail K. Davoren 《Behavioral ecology and sociobiology》2009,63(12):1773-1785
How predators vary search patterns in response to prey predictability is poorly known. For example, marine invertebrates may
be predictable but of low energy value, while fish may be of higher energy value but unpredictable at large (pelagic schools)
or small (solitary benthics) spatial scales. We investigated the search patterns of the thick-billed murre (Uria lomvia), an Arctic seabird feeding on invertebrates, pelagic fish, or benthic fish. Foraging ranges at the Coats Island colony are
generally smaller (<240 min per trip) than at larger colonies, and many birds specialize in foraging tactics and diet. Underwater
search times for benthic fish were higher than for pelagic fish or invertebrates while above-water search times for pelagic
fish were higher than for benthic fish or invertebrates. There were few stops during trips. Total trip time, flying time,
number of flights, and number of dives were intercorrelated and increased with prey energy content, suggesting that longer
trips involved fewer prey encounters due to selection of higher-quality, but rarer, prey items. Flight times were not Lévy-distributed
and seabirds may have used area-restricted searches. The high degree of specialization, apparent absence of information center
effects, and reduced above-water searching times may be linked to the relatively small colony size and the resulting short
commuting distances to feeding areas, leading to greater prey predictability. We concluded that prey predictability over various
scales affected predator search patterns. 相似文献
12.
David Grémillet Clara Péron Jean-Baptiste Pons Ridha Ouni Matthieu Authier Mathieu Thévenet Jérôme Fort 《Marine Biology》2014,161(11):2669-2680
Recent meta-analyses identified conservation hotpots at the scale of the Mediterranean, yet those may be crude by lack of detailed information about the spatial ecology of the species involved. Here, we identify an irreplaceable marine area for >95 % of the world population of the Scopoli’s shearwater (Calonectris diomedea), which is endemic to the Mediterranean and breeds on the island of Zembra off Tunis. To this end, we studied the three-dimensional at-sea movements of 50 breeding adults (over a total of 94 foraging trips) in 2012 and 2013, using GPS and temperature–depth recorders. Feathers were also collected on all birds to investigate their trophic status. Despite Zembra being the largest seabird colony in the Mediterranean (141,000 pairs), the per capita home-range of Scopoli’s shearwaters foraging from this colony was not larger than that of birds from much smaller colonies, indicating highly beneficial feeding grounds in the Gulf of Tunis and off Cap Bon. Considering depleted Mediterranean small pelagic fish stocks, supposed to be Scopoli’s shearwater prey base, we therefore speculate that birds may now also largely feed on zooplankton, something which is supported by our stable isotopic analyses. Crucially, shearwater at-sea feeding and resting areas showed very little overlap with a conservation hotspot recently defined on the western side of the Gulf of Tunis using meta-analyses of species distributions relative to anthropogenic threats. We therefore propose a major extension to this conservation hotspot. Our study stresses the importance of detailed biotelemetry studies of marine megafauna movement ecology for refining large-scale conservation schemes such as marine protected area networks. 相似文献
13.
To determine the effects of prey quantity on central-place foraging of predatory wasps ( Polistes dominulus), prey of varying quality were distributed in patches. A field experiment was conducted, which controlled the amount and quality of prey available. 'Low-fed' colonies were provided with one-third the quantity of prey as that of 'high-fed' colonies. Both were provided with a 1:1 ratio of palatable:unpalatable prey. Experienced wasps of the high-fed colonies never selected unpalatable prey as their first choice of the day, whereas those of the low-fed colonies selected unpalatable prey as their first choice about 1:4 times. In general, wasps from the high-fed colonies reduced palatable patches to zero prey before exploiting unpalatable patches. Foundresses of high-fed colonies captured disproportionately more palatable prey than those of low-fed nests, but there was no correlation between ratio of palatable to unpalatable prey taken and the number of offspring produced. Wasps from low-fed colonies attacked unpalatable prey sooner, but not without considerable effort to avoid use of those patches. Foundresses of low-fed colonies also spent a greater proportion of time overall in unsuccessful search, which may explain why only wasps from low-fed colonies foraged on cool days. High-fed colonies produced more cells and more and heavier offspring than low-fed colonies. But the productivity of the low-fed colonies was greater than that of the 'natural' colonies, which had to find their own prey in a field-woodland area. These results indicate that prey scarcity changes foraging behavior and affects prey choice. These changes may not totally alleviate negative effects of unpalatable prey on colony development and offspring production. The results of this study increase understanding of the central-place foraging behavior of paper wasps, which are important biocontrol agents in natural and agricultural settings. 相似文献
14.
Akiko Shoji Ellie Owen Mark Bolton Ben Dean Holly Kirk Annette Fayet Dave Boyle Robin Freeman Chris Perrins Stéphane Aris-Brosou Tim Guilford 《Marine Biology》2014,161(9):2121-2129
How central-place foragers change search strategy in response to environmental conditions is poorly known. Foragers may vary the total distance travelled and how far they range from the central place in response to variation in the distribution of their prey. One potential reason as to why they would extend the length of their foraging trip and its distance from the colony would be to increase prey quality or quantity, despite incurring higher transit costs. To test this trade-off hypothesis in a species with high flight costs, we recorded the foraging behaviour of razorbills (Alca torca) using state-of-the-art techniques that log both individual horizontal (flight activity) and vertical (dive activity) movements. We show that the distance that razorbills travelled to foraging locations increased with sea-surface temperature, which may relate to higher prey quality or quantity. This relation is supported by an indirect index of patch quality, based on dive profiles, which also increased with travel distance from the colony. Furthermore, we show that this index was highest during the daily peak in diving activity, around midday. Taken together, these results suggest that razorbills are capable of adjusting their search strategies sensitively in response to proximate environmental cues. 相似文献
15.
Hany Alonso José P. Granadeiro Vitor H. Paiva Ana S. Dias Jaime A. Ramos Paulo Catry 《Marine Biology》2012,159(6):1197-1207
In pelagic seabirds, who often explore distant food resources, information is usually scarce on the level of trophic segregation
between parents and their offspring. To investigate this issue, we used GPS tracking, stable isotopes and dietary information
of Cory’s shearwaters Calonectris diomedea breeding in contrasting environments. Foraging trips at Selvagem Grande (an oceanic island) mainly targeted the distant African
coast, while at Berlenga island (located on the continental shelf), shearwaters foraged mainly over nearby shelf waters. The
degree of isotopic segregation between adults and chicks, based on δ13C, differed markedly between the two sites, indicating that adult birds at Selvagem fed their chicks with a mixture of shelf
and offshore pelagic prey but assimilated more prey captured on coastal shelf waters. Isotopic differences between age classes
at Berlenga were much smaller and may have resulted from limited dietary segregation or from age-related metabolic differences.
The diet of shearwaters was also very different between the two colonies, with offshore pelagic prey only being detected at
Selvagem Grande. Our findings suggest that spatial foraging constraints influence resource partitioning between pelagic seabirds
and their offspring and can lead to a parent–offspring dietary segregation. 相似文献
16.
F. Daunt V. Afanasyev J. R. D. Silk S. Wanless 《Behavioral ecology and sociobiology》2006,59(3):381-388
In temperate regions, winter presents animals with a number of challenges including depressed food abundance, increased daily
energy requirements, higher frequency of extreme weather events and shortened day length. Overcoming these constraints is
critical for overwintering survival and scheduling of future breeding of long-lived species and is likely to be state dependent,
associated with intrinsic abilities such as food acquisition rates. We examined the relationship between environmental and
intrinsic factors on overwintering foraging and subsequent breeding phenology of the European shag Phalacrocorax aristotelis, a diurnal marine predator. We tested a range of hypotheses relating to overwintering foraging time and location. We found
that individuals greatly increased their foraging time in winter to a peak of more than 90% of available daylight at the winter
solstice. The seasonal patterns of foraging time appear to be driven by a combination of light levels and weather conditions
and may be linked to the availability of the shag's principal prey, the lesser sandeel Ammodytes marinus. There was no evidence that shags dispersed south in winter to increase potential foraging time. Foraging time decreased
after the winter solstice and, crucially, was correlated with subsequent breeding phenology, such that individuals that spent
less time foraging in February bred earlier. The relationship was much stronger in females than males, in line with their
more direct control of timing of breeding. Our results demonstrate that pre-breeding intrinsic foraging ability is critical
in determining breeding phenology. 相似文献
17.
The diet of the emperor penguin Aptenodytes forsteri in the western Ross Sea during spring was investigated by analysis of stomach contents sampled at three different localities.
At Cape Washington, emperor penguins feeding chicks consistently preyed on fishes (89 to 95% by mass) and crustaceans (5 to
11%) over the four spring seasons examined. By far the commonest prey was the Antarctic silverfish Pleuragramma antarcticum (89% of the fish prey); the remainder of fish prey were mainly unidentified juveniles of different species of channichthyid
fishes. Three species dominated the crustacean part of the diet, i.e. the gammarid amphipods Abyssorchomene rossi/plebs (30% of the crustacean prey) and Eusirus microps (22%), together with the euphausiid Euphausia crystallorophias (24%). At Coulman Island and Cape Roget, fishes, mainly P. antarcticum, formed the bulk of the food (88 and 93% by mass, respectively), crustaceans were minor prey (2.5 and 0.4%), and the squid
Psychroteuthis glacialis accounted for a small but significant part of the food (3.5 and 0.8%). This study emphasizes the importance of the small,
shoaling pelagic fish Pleuragramma antarcticum as a key link between zooplankton and top predators, including seabirds, in the food web and marine ecosystem of the Ross
Sea.
Received: 20 May 1997 / Accepted: 8 October 1997 相似文献
18.
Aposematic species advertise their unpalatability to potential predators using conspicuous warning colouration. The initial evolution of aposematism is thought to occur by warningly coloured mutants emerging in an already unpalatable cryptic species. However, possessing defence chemicals is often costly, and it is difficult to understand what the selective benefits might be for a mutation causing its bearer to be defended in a population of otherwise palatable cryptic prey. One solution to this problem is that chemically defended individuals are tasted and rejected by predators, and are, therefore, more likely to survive predatory attacks than undefended individuals. Using naïve domestic chicks Gallus gallus domesticus as predators and cryptic green chick crumbs as prey, we asked whether the accuracy with which birds discriminated between palatable and unpalatable prey was affected by the palatability of the unpalatable prey (moderately or highly defended), or their frequency in the population (10 or 25%). Birds could discriminate between green prey on the basis of their defences, and showed better discrimination between palatable and unpalatable prey when defended crumbs were highly unpalatable, compared to when they were moderately unpalatable. Although there was no detectable effect of the frequency of unpalatable prey in the population on predator taste-rejection behaviour in our main analysis, frequency did appear to affect the strategies that birds used in their foraging decisions when prey were only moderately unpalatable. How birds used taste to reject prey also suggests that birds may be able to monitor and regulate their chemical intake according to the frequency and defence levels of the unpalatable prey. Taken together, these results show that avian predators can generate selection for unpalatability in cryptic prey by sampling and taste-rejecting prey, but that a relatively large chemical difference between palatable and unpalatable prey may be necessary before unpalatable prey can enjoy a selective advantage. The exact nature of this evolutionary dynamic will depend on other environmental factors, such as defence costs and prey availability, but it provides a mechanism by which defences can evolve in a cryptic population. 相似文献
19.
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
20.
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