Foraging behaviour and reproductive success in Magellanic penguins (Spheniscus magellanicus): a comparative study of two colonies in southern Chile

Marine Biology - During the breeding season 1996/97 we compared the foraging and diving behaviour of adult Magellanic penguins (Spheniscus magellanicus), growth rates of their chicks and their...     

Social foraging by honeybees: how colonies allocate foragers among patches of flowers

Summary To understand how a colony of honeybees keeps its forager force focussed on rich sources of food, and analysis was made of how the individual foragers within a colony decide to abandon or continue working (and perhaps even recruit to) patches of flowers. A nectar forager grades her behavior toward a patch in response to both the nectar intake rate of her colony and the quality of her patch. This results in the threshold in patch quality for acceptance of a patch being higher when the colonial intake rate of nectar is high than when it is low. Thus colonies can adjust their patch selectivity so that they focus on rich sources when forage is abundant, but spread their workers among a wider range of sources when forage is scarce. Foragers assess their colony's rate of nectar intake while in the nest, unloading nectar to receiver bees. The ease of unloading varies inversely with the colonial intake rate of nectar. Foragers assess patch quality while in the field, collecting nectar. By grading their behavior steeply in relation to such patch variables as distance from the nest and nectar sweetness, foragers give their colony high sensitivity to differences in profitability among patches. When a patch's quality declines, its foragers reduce their rate of visits to the patch. This diminishes the flow of nectar from the poor patch which in turn stimulates recruitment to rich patches. Thus a colony can swiftly redistribute its forager force following changes in the spatial distribution of rich food sources. The fundamental currency of nectar patch quality is not net rate of energy intake, (Gain-Cost)/Time, but may be net energy efficiency, (Gain-Cost)/Cost.     

Nest-maintenance effort and health status in chinstrap penguins, Pygoscelis antarctica: the functional significance of stone-provisioning behaviour

Stone provisioning is a nest-maintenance activity accomplished by pygoscelid penguins after reliefs during the incubation/brooding period. The functional significance of this behaviour has been mainly explained as a parental strategy preventing nest flooding under detrimental weather conditions. In addition, and in the light of recent studies, this behaviour could also fit into the sexual selection process. In this study, we tested the first idea, that is, whether stone provisioning is a nest-maintenance behaviour to increase egg/nestling survival by lowering the risk of nest flooding, and can thus be considered a form of parental care. Additionally, we investigated if the effort invested by parents in nest maintenance is constrained by physiologically limiting resources. The effort of stone collection and the perceived risk of nest flooding were experimentally manipulated during the incubation and early brooding phases in a chinstrap penguin, Pygoscelis antarctica, colony. Three groups of nests were established. After weighing, control nests were left unmanipulated. In a second group of nests (reduced group), only one-half of the initial weight of stones was returned to the nests. In a third group of nests (snow-added group), we both reduced nest weight by a half and added snow outside the nest bowl over 6 consecutive days. Ten days after manipulation, the difference in nest weight between initial and final conditions was significantly related to treatment: penguins increased stone provisioning in the reduced group (44% of half-reduced nests), but drastically more in the reduced and snow-added group (123% of half-reduced nests), while the weight of control nests was unchanged compared to premanipulation conditions. The intensity of stone provisioning was affected by nest date, peaking about hatching time and shortly after, and declining with advancing chick age. These results suggest that stone provisioning is a mechanism that has evolved to prevent egg or chick mortality by nest flooding. The haematocrit, but not leukocyte numbers as expressed by the buffy coat layer, varied with the experimental conditions. Penguins investing more time in nest maintenance had a lower haematocrit, suggesting a physiological trade-off probably mediated by competition between the time devoted to nest maintenance versus foraging activities. The amount of stones collected and the haematocrit were positively related to the number of neighbour nests, so those individuals surrounded by more nests seemed to obtain benefits in the availability of nest material and energy savings. This study indicates that stone-provisioning behaviour is a nest-maintenance activity evolved to improve thermal nest characteristics potentially increasing offspring survival, and competing in time and energy with other reproductive activities. Stone provisioning in penguins should therefore be regarded as a form of parental care and an important part of individual reproductive effort in species breeding in harsh environments. Furthermore, nest size and nest-maintenance effort should be considered reproductive traits indicative of parental quality and thus could also be involved in the post-mating sexual selection process.     

Social foraging in stingless bees: how colonies of Melipona fasciata choose among nectar sources

In an experimental set-up, a colony of the stingless bee Melipona fasciata demonstrated its ability to choose the better of two nectar sources. This colony pattern was a result of the following individual behavioural decisions: continue foraging, abandon the feeder, restart foraging and initiate foraging. Only very rarely did individuals switch from one feeder to the other. With the first combination of a rich (2.7 M) and a poor (0.8 M) feeder M. fasciata behaved differently from Apis mellifera. Recruitment occurred to both feeders and the poor feeder was not abandoned completely. When the poor feeder was set to 0.4 M, M. fasciata abandoned the poor feeder rapidly and allocated more foragers to the rich feeder. These patterns were similar to those reported for A. mellifera with the first combination of feeders. Over a sequence of 4 days, experienced bees increasingly determined the colony patterns, and the major function of communication between workers became the reactivation of experienced foragers. The foragers modulated their behaviour not only according to the profitability of the feeder, but also according to previous experience with profitability switches. Thus, experience and communication together regulated colony foraging behaviour. These findings and the results of studies with honeybees suggest that M. fasciata and honeybees use similar decision-making mechanisms and only partly different tools. Received: 21 December 1998 / Accepted: 5 January 1999     

Diving behaviour of Little Penguins from four colonies across their whole distribution range: bathymetry affecting diving effort and fledging success

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.     

Shifting foraging strategies in colonies of the social wasp Polybia occidentalis (Hymenoptera, Vespidae)

Social insect colonies can be expected to forage at rates that maximize colony fitness. Foraging at higher rates would increase the rate of worker production, but decrease adult survival. This trade-off has particular significance during the founding stage, when adults lost are not replaced. Prior work has shown that independent-founding wasps rear the first workers rapidly by foraging at high rates. Foraging rates decrease after those individuals pupate, presumably reducing the risk of foundress death. In the swarm-founding wasps, colony-founding units have many workers, making colony death by forager attrition less likely. Do swarm-founding wasps show similar shifts in foraging rates during the founding stage? We measured foraging rates of the swarm-founding wasp, Polybia occidentalis at four stages of colony development. At each stage, foraging rates correlated with the number of larvae present, which, in the founding stages, correlated with the number of cells in the new nest. Thus, foraging rates appear to be demand-driven, with the level of demand in the founding stage set by the size of nest that is constructed. During the founding stage, foraging rates per larva were high initially, suggesting that colonies minimize the development times of larvae early in the founding stage. Later in the stage, foraging rates decreased, which would reduce worker mortality until new workers eclose. This pattern is similar to that shown for independent-founding wasps and likely results from conflicting pressures to maximize colony growth and minimize the risk of colony death by forager attrition.     

Understanding the distribution of bushmeat hunting effort across landscapes by testing hypotheses about human foraging

Mitigating the massive impacts of defaunation on natural ecosystems requires understanding and predicting hunting effort across the landscape. But such understanding has been hindered by the difficulty of assessing the movement patterns of hunters in thick forests and across complex terrain. We statistically tested hypotheses about the spatial distribution of hunting with circuit theory and structural equation models. We used a data set of >7000 known kill locations in Guyana and hunter movement models to test these methods. Comparing models with different resistance layers (i.e., different estimates of how terrain and land cover influence human movement speed) showed that rivers, on average, limited movement rather than serving as transport arteries. Moreover, far more kills occurred close to villages than in remote areas. This, combined with the lack of support for structural equation models that included latent terms for prey depletion driven by past overhunting, suggests that kill locations in this system tended to be driven by where hunters were currently foraging rather than by influences of historical harvest. These analyses are generalizable to a variety of ecosystems, species, and data types, providing a powerful way of enhancing maps and predictions of hunting effort across complex landscapes.     

Chinstrap penguins alter foraging and diving behavior in response to the size of their principle prey, Antarctic krill

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.     

Evaluating the relative importance of intrinsic and extrinsic factors on the foraging activity of top predators: a case study on female little penguins

A complex interaction of biotic and abiotic factors influences animal foraging activity. It is often difficult to understand which factors may affect animals’ foraging and how it is affected. For instance, whereas the effect of sexual dimorphism on foraging activity has been reported in several species, little is known of the complex interactions between variables acting at a finer scale, e.g. the variability of body mass within a sex. Evaluating the importance of these finer scale factors is also essential to the understanding of foraging behaviour. We propose here a simple approach by applying principal component analysis (PCA) in a novel way to examine relationships between biotic and abiotic factors affecting foraging behaviour of top predators. We studied female little penguins (Eudyptula minor) of known age, carrying miniature accelerometers during the guard stage of breeding. Surprisingly, the body mass of the females did not influence any of the foraging parameters, but females foraging later in the breeding season dived shallower and more often, showing a strong correlation with laying date. Similarly, the diving effort of females was greater with increasing chick age within the same breeding stage. These results indicate that for female little penguin, the relationship between changes in prey availability and hunting effort can change at a fine scale, within a breeding stage. Therefore, any analysis of little penguin foraging behaviour during breeding should consider the timing in relation to the breeding season. We encourage researchers to develop the use of this PCA approach as it could help clarify the complexity of the underlying mechanisms determining foraging activity and we propose that it should be used as a first step of foraging behaviour analysis, before examining a particular relationship.     

Regulation of pollen foraging in honeybee colonies: effects of young brood, stored pollen, and empty space

Pollen storage in a colony of Apis mellifera is actively regulated by increasing and decreasing pollen foraging according to the “colony's needs.” It has been shown that nectar foragers indirectly gather information about the nectar supply of the colony from nestmates without estimating the amount of honey actually stored in the combs. Very little is known about how the actual colony need is perceived with respect to pollen foraging. Two factors influence the need for pollen: the quantity of pollen stored in cells and the amount of brood. To elucidate the mechanisms of perception, we changed the environment within normal-sized colonies by adding pollen or young brood and measured the pollen-foraging activity, while foragers had either direct access to them or not. Our results show that the amount of stored pollen, young brood, and empty space directly provide important stimuli that affect foraging behavior. Different mechanisms for forager perception of the change in the environment are discussed. Received: 13 June 1998 / Accepted after revision: 25 October 1998     

Comparison of diving behavior and foraging habitat use between chinstrap and gentoo penguins breeding in the South Shetland Islands, Antarctica

Chinstrap, Pygoscelis antarctica, and gentoo, P. papua, penguins are sympatric species that inhabit the Antarctic Peninsula. To evaluate differences in the foraging habitat of these two species, we recorded their foraging locations and diving behavior using recently developed GPS-depth data loggers. The study was conducted on King George Island, Antarctica during the chick-guarding period of both species, from December 2006 to January 2007. The area used for foraging, estimated as the 95% kernel density of dive (>5 m) locations, overlapped partially between the two species (26.4 and 68.5% of the area overlapped for chinstrap and gentoo penguins, respectively). However, the core foraging area, estimated as the 50% kernel density, was mostly separate (12.8 and 25.0% of the area overlapped for chinstrap and gentoo penguins, respectively). Chinstrap penguins tended to use off-shelf (water depth > 200 m) regions (77% of the locations for dives >5 m), whereas gentoo penguins mainly used on-shelf (water depth < 200 m) areas (71% of dive locations). The data on foraging locations, diving behavior, and bathymetry indicated that gentoo penguins often performed benthic dives (28% of dives >5 m), whereas chinstrap penguins almost always used the epipelagic/mid-water layer (96% of dives >5 m). Diving parameters such as diving bottom duration or diving efficiency differed between the species, reflecting differences in the use of foraging habitat. The diving parameters also suggested that the on-shelf benthic layer was profitable foraging habitat for gentoo penguins. Conversely, the relationship between trip duration, date, and stomach content mass suggested that the chinstrap penguins went further from the colony to forage as the season progressed, possibly reflecting a reduction in prey availability near the colony. Our results suggest that chinstrap and gentoo penguins segregated their foraging habitat in the Antarctic coastal marine environment, possibly due to inter- and intra-specific competition for common prey resources.     

Adjustment of parental effort to manipulated foraging ability in a pelagic seabird,the thin-billed prion Pachyptila belcheri

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.     

Ontogeny of early diving and foraging behavior of northern fur seal (Callorhinus ursinus) pups from Bering Island,Russia

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.     

Cephalopod remains from the stomach of a sperm whale stranded off Patagonia

The stomach of a male sperm whale (Physeter macrocephalus) stranded near Comodoro Rivadavia, Argentina, on 21 March 1986, contained 247 cephalopod beaks (128 upper and 119 lower). The lower beaks were identified, their rostral lengths were measured and used to estimate the mantle lengths and wet weight of the representatives of each cephalopod taxon. Fifteen species from nine families were represented. The most numerous species, in order of decreasing abundance, were the large cranchiidMesonychoteuthis hamiltoni (32.8% of total numbers),Mastigoteuthis sp. A (16.0%), andKondakovia longimana andHistioteuthis atlantica (both 13.5%). Almost 85% of the estimated total weight was contributed by two species,Mesonychoteuthis hamiltoni (61.6%) andK. longimana (23.1%). The presence of beaks fromK. longimana, Alluroteuthis antarcticus andM. hamiltoni, which are all thought to be restricted to the Antarctic, suggests that the whale had migrated North prior to stranding.     

Long-term behavior at foraging sites of adult female loggerhead sea turtles (Caretta caretta) from three Florida rookeries

We used satellite telemetry to study behavior at foraging sites of 40 adult female loggerhead sea turtles (Caretta caretta) from three Florida (USA) rookeries. Foraging sites were located in four countries (USA, Mexico, the Bahamas, and Cuba). We were able to determine home range for 32 of the loggerheads. One turtle moved through several temporary residence areas, but the rest had a primary residence area in which they spent all or most of their time (usually >11 months per year). Twenty-four had a primary residence area that was <500 km² (mean = 191). Seven had a primary residence area that was ≥500 km² (range = 573–1,907). Primary residence areas were mostly restricted to depths <100 m. Loggerheads appeared to favor areas with larger-grained sediment (gravel and rock) over areas with smaller-grained sediment (mud). Short-term departures from primary residence areas were either looping excursions, typically involving 1–2 weeks of continuous travel, or movement to a secondary residence area where turtles spent 25–45 days before returning to their primary residence area. Ten turtles had a secondary residence area, and six used it as an overwintering site. For those six turtles, the primary residence area was in shallow water (<17 m) in the northern half of the Gulf of Mexico (GOM), and overwintering sites were farther offshore or farther south. We documented long winter dive times (>4 h) for the first time in the GOM. Characterizing behaviors at foraging sites helps inform and assess loggerhead recovery efforts.     

Composition,structure and productivity of neritic plankton communities near the bird colonies of the northern shores of Novaya Zemlya

A survey was made of coastal waters around the colonies of Arctic sea birds, which showed that such zones are highly productive. The mean biomass (standing stock) of crustacean plankton for the whole water column varied from 470 to 670 mg/m³ in separate transects, its maxium value reaching 1950 mg/m³. A list of species is given. Dominance hierarchy among the species is clearly expressed. The stable discrete structure of the community is assured by the spatial disjunction of dominant-form populations and the existence of the latter as relatively isolated aggregations. The conclusions arrived at are based on the materials of net hauls and analyses of the food of planktophageous birds (Plotus alle, family Alcidae). Favourable hydrological factors in conjunction with the fertilization of water with bird guano assure the stability of this neritic community with its multiplicity of interrelationships between producers and consumers of the first and second trophic levels, existing under the rigorous conditions of an ice-covered region.     

Winter migration of magellanic penguins (Spheniscus magellanicus) from the southernmost distributional range

A total of 22 magellanic penguins (Spheniscus magellanicus) from Isla Martillo in the Beagle Channel, Argentina, were successfully satellite tracked in 2004 (n = 7), 2005 (n = 7) and 2006 (n = 8) to monitor their winter migration after moult. Only one magellanic penguin migrated northwards into the Pacific Ocean, whereas all others remained in the Atlantic Ocean. In general, these birds left the island in an easterly direction, rounded Cabo San Diego, the southeasterly tip of South America, and continued northwards occupying inshore waters mostly less than 50 km from the coast, only occasionally venturing further offshore. By the end of the transmission period, birds were still travelling northwards and the most northerly positions were obtained from birds located in the area of Peninsula Valdés, Argentina, at a latitude of around 42°S, some 1,500 km from their breeding site on Isla Martillo. The mean maximum distance to the breeding site was, however, only 624 ± 460 km. The mean minimum distance covered during the study period was 1,440 ± 685 km, which corresponded to a mean distance of 23.2 ± 6.6 km covered per day. The northbound migration of the penguins could be separated into periods of rapid movement, interspersed with periods during which the birds remained for some time in particular coastal regions. Areas with a high density of daily penguin positions were observed in three distinct areas: at the northeastern coast of Tierra del Fuego, at the southern entrance of Golfo San Jorge and to the northeast of the Peninsula Valdez. The observed migration pattern is presumably driven by the formation and subsequent dispersal of areas of enhanced productivity as the season progressed. Our findings also suggest that magellanic penguins are increasingly threatened by human activities in coastal areas as penguins migrate northwards.     

Reproduction and imposex in the edible snail <Emphasis Type="Italic">Adelomelon ancilla</Emphasis> from northern Patagonia,Argentina

The edible volutid snail Adelomelon ancilla occurs on the Argentine coast and may have the capacity to serve as source of support for local fisheries. However, knowledge of its reproduction is lacking. Over 3 years (from September 2000 to July 2004) we studied the oviposition at Golfo Nuevo, Patagonia by diving. Monthly collections were performed to examine gonadal stages histologically during 2002–2003. Gamete development stages corresponded with the expected period for oviposition occurring from July to November, a time of increasing day length. Oviposition also took place in March when water temperature attained a maximum of 18°C. Following the spawning period, remaining gametes were resorpted in both sexes. Males contained sperm throughout the year, parasperm and eusperm forms were found within the same acinus. Oogonia/oocytes ranged from 20 to 240 μm in diameter during oogenesis. Females commenced laying egg capsules from a shell length of 114 mm. Reproduction is compared with other fishable volutid snails from the Argentine shelf, and suggests the need to apply certain fishing restrictions if the resource begins to be utilized commercially. The imposex condition was found in snails from some shipping areas. The frequency of this condition declined with distance from the port.     

Stable isotope variation in the northern Gulf of Mexico constrains bottlenose dolphin (Tursiops truncatus) foraging ranges

Site-specific differences were found in consumer isotope values among ten sites examined in the northern Gulf of Mexico. Average δ¹³C values among sites ranged ?21.7 to ?15.7 ‰, δ¹⁵N ranged <3 ‰: from 9.8 to 11.5 ‰, and δ³⁴S ranged from 5.9 to 18.3 ‰. Isotope variation among these sites provided insight into the ranging habits of bottlenose dolphins (Tursiops truncatus) sampled in St. George Sound (29.8N, 84.6W), a nearshore seagrass habitat, during May of 2005. Isotope comparisons suggest that the majority of dolphins sampled (average ± one standard deviation: δ¹³C = ?17.5 ± 0.8, δ¹⁵N = 14.5 ± 0.9, and δ³⁴S = 10.6 ± 1.5) did not forage significantly on offshore species which are significantly ³⁴S-enriched, nor is it likely that they ranged either eastward or westward along the coast within the sampling region. Despite their capability for ranging, these dolphins occupied a restricted home range, during the spring before our sampling efforts. These results demonstrate significant fine-scale isotope variation among coastal habitats explained by differences in freshwater inputs, organic matter loading, and modes of primary production that may be used to constrain the foraging ranges of a highly mobile apex predator.