Transition to independence and evidence of extended parental care in the gentoo penguin (<Emphasis Type="Italic">Pygoscelis papua</Emphasis>)

We used radio telemetry and observations to study the activity patterns and behavior of gentoo penguin chicks at Admiralty Bay, King George Island, South Shetland Islands in 2005 during their “fledging period”; defined as the time between a chick’s first trip to sea and its final dispersal from the breeding colony. Gentoo penguins exhibited delayed dispersal of young and extended parental provisioning, behaviors not observed in other Pygoscelis species. Chicks took their first trip to sea at a mean age of 70 days of age, before finally departing the colony at a mean age of 82 days. During this fledging period, individual chicks made an average of five trips to sea. Trip duration increased significantly as chicks aged, with trips to sea becoming similar to literature values of adult foraging trips in both timing and duration. Behavioral observations and mass dynamics confirmed that many chicks were still being fed during this fledging period, with parental feeding behaviors most often observed in the late afternoon to evening hours. We hypothesize that these behaviors provide an opportunity for chicks to gain experience at sea prior to dispersal and might allow them to develop foraging skills before they are completely independent.     

Fighting behavior in hermit crabs: the combined effect of resource-holding potential and resource value in Pagurus longicarpus

A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of equal/different RHP (i.e. ‘body size’) and equal/different RV (i.e. ‘shell size’ and ‘shell quality’). In a fifth experiment, dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min. As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory of the previously held resource and behaved accordingly.     

Claw allometry in green crabs, Carcinus maenas: heterochely, handedness, and sex

Claw loss and reversal of handedness during regeneration are common phenomena in heterochelous decapod crustaceans, which typically have one large ‘crusher’ claw on the right side and a smaller ‘cutter’ claw on the left. Little is known about the relative importance of claw growth vs. body growth during claw regeneration. Here the relationship between claw size and body size of green crabs, Carcinus maenas, was examined to test for differences in claw allometry as a function of handedness and sex, as there are differences in how males and females use their claws. A total of 730 crabs (range = 15.7–83.6 mm CW) were collected from Maine to New Jersey, USA from May to October 1997, 2000, and 2004–2005. Claw growth, particularly crushers, was accelerated in left-handed crabs and in males compared to right-handed crabs and females respectively. These differing growth strategies highlight the role of sexual dimorphism in claw usage and the importance of achieving heterochely after claw injury. These results imply that handedness should be an important factor to consider in future studies of crab morphology, behavior, and morphometrics. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Central place foraging by breeding Cook’s petrel Pterodroma cookii: foraging duration reflects range, diet and chick meal mass

Pelagic seabirds are central place foragers during breeding and variation in foraging trip duration and range reflect differences in diet and chick provisioning, through the exploitation of divergent habitats of varying productivity. We tested whether these relationships hold in small procellarriids by equipping chick-rearing Cook’s petrel Pterodroma cookii (200 g) with geolocation-immersion loggers, conducting isotope analysis of blood and measuring chick meal mass following foraging trips of varying duration. Cook’s petrel tracked during chick rearing from Little Barrier Island (LBI) and Codfish Island (CDF), New Zealand had larger maximum ranges during longer foraging trips. Blood nitrogen isotope signatures (δ¹⁵N) of adults were significantly higher after foraging trips of longer duration, but not of greater maximum range. There was no significant relationship between blood carbon isotope signatures (δ¹³C) and foraging trip characteristics. Proportion of time spent on the sea surface and the mass of the meal brought back to chicks were consistently greater for Cook’s petrel with larger maximum ranges, which in the case of birds from CDF coincided with productive subtropical convergence zone habitats. As predicted, trip duration reflected divergent foraging behaviours in Cook’s petrel during breeding. We suggest that the availability of different prey is a key factor governing at-sea distributions and dietary composition of this species.     

Mating behavior of <Emphasis Type="Italic">Abdopus aculeatus</Emphasis> (d’Orbigny 1834) (Cephalopoda: Octopodidae) in the wild

The mating system of Abdopus aculeatus incorporates sneaker matings, mate guarding, sex-specific body patterns, frequent copulations, and male–male competition for mates, making it more similar to that of aggregating decapod cephalopods than any previously known octopus social system. Large male–female A. aculeatus occupy ‘Adjacent’ (G_A) dens and copulate frequently in mate-guarding situations over successive days. Nearby individuals copulate in ‘Temporary guarding’ (G_T) and ‘Transient’ (T; non-guarding) situations, the latter of which can involve ‘Sneaker’ (S) mating. In a focal animal study of these octopuses in the wild (Sulawesi, Indonesia) we addressed the hypotheses that they demonstrate: (1) precopulatory mate choice, (2) differential copulation rates by individuals employing different mating tactics, and (3) distant sex identification. We quantified daily copulation rates of A. aculeatus of reproductive size as well as aspects of copulation duration, display, mate-competition, and mate rejection. Mating tactic correlated with daily copulation rates. ♂G_A spent significantly more time copulating than did ♂T, while ♀G_A spent more than twice as much time per day in copula than did other females. Sneaker copulations lasted longer than those by males adopting other tactics. Mate-guarding was an effective and important tactic used by males to temporarily monopolize mating with apparently non-selective females. Males demonstrated clear pre-copulatory mate choice by guarding and mating repeatedly with large females (typically ♀G_A). While foraging alone away from the den, ♂G procured ‘Transient’ copulations with unguarded females. However, mate-guarding reduced the amount of time ♂G were alone and may impede their ability to seek out new mates. Low-copulation rates by ♀T, the smallest female tactic on average, may reflect this trade-off between mate preference and mate-searching by males, or non-receptivity of some females. A male-typical body pattern (black and white stripes) appeared to facilitate distant sex identification. Although mating and aggression were often initiated before contact between individuals, same-sex copulations and intense male–female aggression were rare. By contrast frequent male–female copulations and intense male–male aggression were consistent behavioral components of mating in A. aculeatus at these sites. Because the behavioral and ecological characters conducive to this complex system are not exclusive to A. aculeatus, it is possible that other octopuses exhibit some or all of these behaviors. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Brood neglect and contingent foraging behavior in a pelagic seabird

Among species where there is a risk to leaving offspring unattended, parents usually take alternating shifts guarding their young. However, they may occasionally exhibit brood neglect by leaving their offspring unattended at the nest. To investigate this phenomenon further, we examined the foraging behavior of the northern gannet (Morus bassanus) during chick-rearing. This species has a prolonged nestling period (13 weeks) and the single chick is usually guarded by one or other of its parents, because unattended chicks are frequently attacked by conspecifics. We tested the prediction that the foraging behavior of adults when they left their offspring alone at the nest (unattended trips) would differ in character to when adults left offspring with their partner (attended trips). Brood neglect typically occurred after a longer-than-average attendance period at the nest. Unattended trips were, on average, about half the duration of attended trips, and therefore much closer to the colony. There was also a difference in departure direction between attended and unattended trips, with unattended trips tending to be northeast of the colony. Chicks were fed by parents after both attended and unattended trips, but the frequency and the duration of unattended trips increased as chicks grew older whereas the duration of attended trips decreased as chicks grew. These results indicate that parents may be making a trade-off between risk of attack to their offspring and food-intake rate, and that the solution to this trade-off is dependent on chick age.Communicated by C. Brown     

Experimental evaluation of the energy balance in Octopus vulgaris, fed ad libitum on a high-lipid diet

A complete energy balance equation was estimated for the common octopus Octopus vulgaris at a constant temperature of 20°C, fed ad libitum on anchovy fillet (Engraulis encrasicolus). Energy used for growth and respiration or lost with faeces and excreted ammonia was estimated, along with total energy consumption through food, for six specimens of O. vulgaris (with masses between 114 and 662 g). The energy balance equation was estimated for the specimens at 10-day intervals. During each 10-day interval, food consumed, body mass increase and quantity of faeces voided were measured. The calorific values of octopus flesh, anchovy flesh and faeces were measured by bomb calorimetry. Oxygen consumption and ammonia excretion rates were monitored for each specimen during three 24-h experiments and daily oxygen consumption and ammonia excretion were estimated. It was found that 58% of the energy consumed was used for respiration. The amount of energy invested in somatic and gonadal growth represented 26% of the total energy budget. The energy discarded through faeces was 13% of consumed energy. The estimated assimilation efficiency (AE) values of O. vulgaris feeding on anchovy (80.9–90.7%) were lower than the AE values estimated for other cephalopod species with different diets of lower lipid content such as crabs or mussels. Specific growth rates (SGR) ranged 0.43–0.95 and were similar to those reported for other high-lipid diets (bogue, sardine) and lower than SGR values found for low-lipid, high-protein diets (squid, crab, natural diet). Ammonia excretion peak (6 h after feeding) followed the one of oxygen consumption (1 h after feeding). The values of atomic oxygen-to-nitrogen (O:N) ratio indicated a protein-dominated metabolism for O. vulgaris.     

Physiological stress responses in the edible crab, <Emphasis Type="Italic">Cancer pagurus</Emphasis>, to the fishery practice of de-clawing

We examined physiological stress responses in the edible crab, Cancer pagurus, subjected to the commercial fishery practice of manual de-clawing. We measured haemolymph glucose and lactate, plus muscular glycogen and glycogen mobilisation, in three experiments where the crabs had one claw removed. In the first, crabs showed physiological stress responses when ‘de-clawed’ as compared to ‘handled only’ over the short term of 1–10 min. In the second, de-clawing and the presence of a conspecific both increased the physiological stress responses over the longer term of 24 h. In the third, de-clawing was shown to be more stressful than ‘induced autotomy’ of claws. Further, the former practice caused larger wounds to the body and significantly higher mortality than the latter. Since the fishery practice is to remove both claws, the stress response observed and mortality data reported are conservative.     

Behavioural responses of the Dungeness crab, <Emphasis Type="Italic">Cancer magister</Emphasis>, during feeding and digestion in hypoxic conditions

The Dungeness crab, Cancer magister, inhabits areas that are frequently subject to periods of hypoxia. This species can employ physiological mechanisms that allow it to cope with acute hypoxic episodes. When crabs feed there is a general increase in physiological variables; these may pose an additional physiological burden on crabs already attempting to maintain adequate oxygen uptake in hypoxia. In Barkley Sound, British Columbia, the inshore habitats of C. magister ranged in dissolved oxygen from 28 kPa at the water surface to less than 1.0 kPa just above the sediment–water interface. During short-term hypoxic events, crabs reduced both the amount of food eaten and the amount of time spent feeding. Crabs tended to cease feeding below 3.2 kPa oxygen, but resumed feeding when the dissolved oxygen tensions were rapidly raised to 6 kPa. In a high (10.5–21 kPa) oxygen gradient, both unfed and fed crabs showed no preference for any area of the gradient. In a low (2.5–10.5 kPa) dissolved oxygen gradient, both unfed and fed crabs preferred the highest oxygen regime. In the laboratory, crabs were less likely to enter hypoxic waters (below 3.2 kPa oxygen) to obtain and consume food; those that did moved the food to a higher oxygen regime prior to feeding and settled in higher oxygen regimes for digestion. Crab behaviour was also monitored in the field. Fed and unfed crabs were fitted with ultrasonic telemetry tags and tracked during a tidal cycle. Unfed crabs remained mobile, travelling up to 1,370 m within 6 h, while postprandial crabs settled in areas of high oxygen and moved very little during the first 48 h after release. The present study suggests that C. magister exhibits behavioural responses in order to minimise the use of physiological mechanisms, and maximise foraging and digestive processes. Thus the nutritional state of the individual may be important in regulating both its behaviour and distribution in its natural environment.     

Spatial and temporal patterns of habitat use by Eurasian oystercatchers (<Emphasis Type="Italic">Haematopus ostralegus</Emphasis>) in the eastern Wadden Sea revealed using GPS data loggers

Detailed knowledge on species–habitat relationships is of crucial importance for the understanding of processes in marine ecosystems. Being top-predators, birds are important bio-indicators for marine systems. The aim of this study was to elucidate precise information on foraging habitat use and foraging times of oystercatchers (Haematopus ostralegus) on wide tidal flats using global positioning system (GPS) data loggers. The study was conducted to collect hints for the negative population trends in oystercatchers in the Wadden Sea. It is the first time that GPS technique has been used in a shorebird species. Although oystercatchers are known to exhibit foraging site fidelity, a number of individuals visited multiple sites. Foraging trips at night were longer, and the targeted sites were further away than those used during the day. These patterns were likely to be caused by higher risks of clutch predation by avian predators during the day that led adults to reduce their absence to defend their clutches. Our methodological approach enabled the subtle spatio-temporal patterns of habitat use to be determined on a very fine spatio-temporal scale. We suggest further potential studies using GPS data loggers that may help to reveal the reasons for the current declines in oystercatcher populations in the German Wadden Sea.     

Oceanographic characteristics of areas used by Cory’s shearwaters during short and long foraging trips in the North Atlantic

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.     

Foraging in the seed-harvester ant genus Pogonomyrmex: are energy costs important?

Energy intake and expenditure on natural foraging trips were estimated for the seed-harvester ants, Pogonomyrmex maricopa and P. rugosus. During seed collection, P. maricopa foraged individually, whereas P. rugosus employed a trunk-trail foraging system. Energy gain per trip and per minute were not significantly different between species. There was also no interspecific difference in energy cost per trip, but energy cost per minute was lower for P. maricopa foragers because they spent on average 7 min longer searching for a load on each trip. Including both unsuccessful and successful foraging trips, average energy gain per trip was more than 100 times the energy cost per trip for both species. Based on this result, we suggest that time cost incurred during individual foraging trips is much more important than energy cost in terms of maximizing net resource intake over time. In addition, because energy costs are so small relative to gains, we propose that energy costs associated with foraging may be safely ignored in future tests of foraging theory with seed-harvesting ant species.     

Diving behaviour of female northern rockhopper penguins, Eudyptes chrysocome moseleyi, during the brooding period at Amsterdam Island (Southern Indian Ocean)

The pattern and characteristics of diving in 14 female northern rockhopper penguins, Eudyptes chrysocome moseleyi, were studied at Amsterdam Island (37°50′S; 77°31′E) during the guard stage, using electronic time–depth recorders. Twenty-nine foraging trips (27 daily foraging trips and two longer trips including one night) with a total of 16 572 dives of ≥3 m were recorded. Females typically left the colony at dawn and returned in the late afternoon, spending an average of 12 h at sea, during which they performed ∼550 dives. They were essentially inshore foragers (mean estimated foraging range 6 km), and mainly preyed upon the pelagic euphausiid Thysanoessa gregaria, fishes and squid being only minor components of the diet. Mean dive depth, dive duration, and post-dive intervals were 18.4 m (max. depth 109 m), 57 s (max. dive duration 168 s), and 21 s (37% of dive duration), respectively. Descent and ascent rates averaged 1.2 and 1.0 ms⁻¹ and were, together with dive duration, significantly correlated with dive depth. Birds spent 18% of their total diving time in dives reaching 15 to 20 m, and the mean maximum diving efficiency (bottom time:dive cycle duration) occurred for dives reaching 15 to 35 m. The most remarkable feature of diving behaviour in northern rockhopper penguins was the high percentage of time spent diving during daily foraging trips (on average, 69% of their time at sea); this was mainly due to a high dive frequency (∼44 dives per hour), which explained the high total vertical distance travelled during one trip (18 km on average). Diving activity at night was greatly reduced, suggesting that, as other penguins, E. chrysocome moseleyi are essentially diurnal, and locate prey using visual cues. Received: 9 December 1998 / Accepted: 3 March 1999     

Circadian shelter occupancy patterns and predator–prey interactions of juvenile Caribbean spiny lobsters in a reef lagoon

The spiny lobster, Panulirus argus, is predominantly nocturnal, remaining inside shelters during the day and foraging outside at night, presumably to minimize predation risk. Predation risk generally decreases with increasing lobster size. Therefore, this study examined the hypothesis that size would influence this basic circadian pattern. Video cameras continuously recorded the shelter occupancy of juvenile lobsters (n = 72) having a carapace length (CL) of 30–62 mm that were tethered to shelters in a shallow reef lagoon. The lobsters’ shelter occupancy was 100% during the day, but declined linearly from shortly before sunset to a minimum of 50% shortly after midnight and then increased linearly, reaching 100% by 1 h after sunrise. The percent time the lobsters spent in the shelters followed a similar trend, but there was wide variability at night (0–100%) for individual lobsters. Lobsters left their shelters 2–30 times night⁻¹, with a majority of excursions lasting <10 min. These results suggest that juvenile P. argus minimize predation risk by remaining in their shelters as long as possible but offset the energetic cost of this behavior by foraging close to their shelters for several short periods at night. This emergence pattern contrasts with those of early benthic phase lobsters (<15 mm CL), which seldom leave their shelters, and adults (>80 mm CL), which have a dusk/early evening peak in activity and leave the shelter for extended periods of time during the night. Furthermore, a minimum shelter occupancy in the middle of the night appears especially well adapted to avoid exposure to daytime predators. Videotaped observations also included interactions between lobsters and two dominant lobster predators, the triggerfish, Balistes capriscus, and the octopus Octopus cf. vulgaris. Lobsters responded differently to these predators: remaining in the shelter when attacked by a triggerfish and fleeing the shelter when attacked by an octopus. Triggerfish were nearly twice as likely to attack a lobster that was outside of the shelter than inside. Once under attack, however, a lobster had nearly the same chance of surviving if it was inside or outside. Results suggest that the patterns of shelter use and emergence change as lobsters grow, probably reflecting the interplay between perception of predation risk and the need to forage. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Epibiosis on cerith shells in a seagrass bed: correlation of shell occupant with epizoite distribution and abundance

The cerith Cerithium atratum (Born 1778) is an abundant gastropod in the seagrass beds at Cabo Frio, Brazil. In order to estimate the ecological importance of cerith shells as a rare hard substratum in the seagrass bed, the abundances of C. atratum and of cerith shells occupied by hermit crabs were quantified. The mean densities of C. atratum and hermit crabs were 1887 and 100 individuals m⁻², respectively, and these provided 0.5 m² shell area m⁻² available for epizoite colonization. The tube-forming polychaete Hydroides plateni (Kinberg 1867) and oyster Ostrea puelchana Orbigny, 1841 were the dominant visible epizoites on inhabited cerith shells. These epizoite populations were compared in order to investigate whether the temporal and spatial patterns in the epibiotic community were related to ecological and behavioral aspects of the occupant species (cerith or hermit crab). Larger cerith shells had a greater abundance of epizoites. Each epizoite showed a preference for a different occupant of the shells (the oyster for C. atratum and the polychaete for cerith shells occupied by hermit crabs). The oyster showed a seasonal pattern in abundance on C. atratum, being more common in fall (March–April). The distribution of the epizoites on the shells depended on the shell occupant species and was probably related to their different foraging activity –C. atratum ploughs half buried through the sediment, while the hermit crab crawls on the sediment surface. In both cases, the activity of the shell occupant was considered to be beneficial to the epizoites, as empty shells and shell fragments did not support a macroepifauna. Received: 1 May 2000 / Accepted: 8 August 2000     

Population ecology of the mud crab <Emphasis Type="Italic">Scylla paramamosain</Emphasis> (Estampador) in an estuarine mangrove system; a mark-recapture study

Mud crabs of the genus Scylla are commercially important mangrove residents that are extensively fished throughout their range in the Indo-West Pacific. Despite this high level of exploitation very little is known about the population dynamics of any of the Scylla species. The present study concentrated on an exploited population of Scylla paramamosain in a natural estuarine mangrove on Can Coc Island in the mouth of the Hau River, Mekong Delta, Vietnam. A total of 6,114 juvenile crabs captured on the seaward mangrove fringe were internally tagged by injection of coded microwire tags and released over a period of 29 days. Recaptures were monitored over the following 144 days. There was little migratory movement within the estuary; of 285 recaptured crabs, 93% were recovered within the island mangrove study area and only two individuals were recovered from mangroves lining the opposite mainland riverbanks. A von Bertalanffy growth function was fitted to growth increment data from recaptured crabs, with L _max = 150 mm to derive a growth constant, k = 2.39 year⁻¹. The theoretical age at which carapace width is zero (t ₀) was derived from known size at recruitment at instar 1, giving a value of −0.0095 years. Previous studies of the same population have shown that female S. paramamosain reach maturity at a mean size of 102 mm carapace width. The present study indicates that they attain this size at around 160 days from first settlement in the mangrove fringe. Abundance of juvenile crabs in the study area was estimated by the Petersen method as 1,101,500 (95% CI 4,17,300–1,785,800, representing 1,102 crabs ha⁻¹ of mangrove. Estimation of mortality from tag returns and from the age-catch curves during a period of constant recruitment were comparable (Z = 1.11 and 1.04 month⁻¹, respectively). Fishing only accounted for 14% of total mortality, suggesting that at the time exploitation was not at a critical level despite the apparent high level of fishing activity.     

Provisioning behavior and the estimation of investment ratios in a solitary bee,Calliopsis (Hypomacrotera) persimilis (Cockerell) (Hymenoptera: Andrenidae)

Summary One aspect of behavioral ecology that has received considerable attention, especially by students of social insects, is the relative amount of energy invested by parents in the rearing of male versus female offspring. Sexual selection theory makes predictions about how individuals should allocate their total investment in the sexes. To test these predictions we must accurately quantify the relative cost incurred by a parent in the production of an average individual of either sex. Body weight ratios are the most common estimate of cost ratio, but the correspondence between offspring body weight and energetic investment on the part of the parent has rarely been determined. Calliopsis (Hypomacrotera) persimilis is a solitary, ground-nesting bee whose natural history makes it particularly convenient for studies of investment patterns and foraging behavior. Each day females construct and provision from 1 to 6 cells in linear, closely-spaced series. Each cell is provisioned with pollen from Physalis Wrightii flowers, which is collected on two or three foraging trips. However, the temporal sequence in which two- and three-trip foraging bouts occur is not random. Females invariably begin each day provisioning cells with three trips worth of pollen and usually switch to provisioning the latter cells of the day with just two trips worth of pollen. The sex of the offspring within the same co-linear series of cells also varies non-randomly — female offspring predominate in the first cells of each series and male offspring in the latter cells. The correspondence between the number of foraging trips to provision a cell, the total time spent foraging, and offspring sex was determined for 36 cells. The data indicate a close, though not absolute, relationship between the number of foraging trips and the sex of the offspring: males usually received two trips of pollen, though some received three, whereas female offspring invariably received three trips worth of pollen. A number of potential estimates of the relative cost of female and male offspring production were calculated. Estimates of the cost ratio based on the amount of time spent foraging, adult dry body weight, and pollen ball dry weight all give similar values. Female offspring receive an energetic investment of from 1.3 to 1.5 times that of males. These results support the use of adult dry body weight ratios in the estimation of cost ratios.     

Energy balance of <Emphasis Type="Italic">Octopus maya</Emphasis> fed crab or an artificial diet

The present study was designed to evaluate the effect of a natural prey (the crab Callinectes sp.) and an artificial diet (pellet with squid paste and offered as a paste) on the survival and assimilation efficiency of subadult octopuses with 486 g of initial live weight. In order to reach this goal, the effects of the type of diet on energetic balance were assessed by recording ingestion rate (C), respiratory rate (R = R routine, R _rout + R apparent heat increment, R _AHI), ammonia production rate (U = U routine, U _rout + U post-prandial, U _PP) and biomass production (P) of Octopus maya during its growing process. Energy lost from faeces (H) was calculated as H=C−(U+R+P) and assimilated energy (As) as R + P. Octopuses fed an artificial diet had almost five times higher ingestion rate compared to that observed in octopuses fed crab. However, growth rate and production (P) were high in octopuses fed crab in comparison to octopuses fed artificial diet. An inverse relation between faeces (H) and type of food was observed, indicating that animals lost 77% of the ingested energy when fed artificial diet and only 5% when fed crab. A higher assimilation and production efficiency were obtained in octopuses fed crab (P/As: 61%) than in animals fed the artificial diet (P/As: −5%). The routine O : N ratio for animals in fasting was 9.1 and 2.3 for octopuses being fed crabs and the artificial diet, respectively. The post-alimentary O : N ratio was 3.6 and 2.2 for animals fed crabs and the artificial diet, respectively. This indicates that animals fed on both diets rely almost exclusively on protein. Based on energy balance data, a value of 472 kJ week⁻¹ kg⁻¹ of live octopus was estimated as the energy needed to obtain a growth rate near 9 g day⁻¹ (2.8% BW day⁻¹) for O. maya subadults. The total crab biomass needed to obtain 1 kg of fed O. maya biomass was calculated. A comparison with other different energy balance measurements made in other octopus species indicates that O. maya and Enteroctopus megalocyathus (Pérez et al. 2006) tend to be more efficient by channelling more ingested energy to biomass production (P = 69.5% of C) than O. vulgaris (P = 23% of C; Petza et al. 2006) or Paraledone charcoti (P = 4% of C; Daly and Peck 2000).     

Effects of interactions among genotypically diverse nestmates on task specialization by foraging honey bees (Apis mellifera)

Summary Recent studies have shown that differences in patterns of task specialization among nestmate honeybee workers (Apis mellifera) can be explained, in part, as a consequence of genotypic variability. Here, we present evidence supporting the hypothesis that an individual's pattern of task specialization is affected not only by her own genotype, but, indirectly, by the genotypes of her nestmates. Workers from two strains of honey bees, one selected for high pollen hoarding, the other for low pollen hoarding, were observed in colonies of their respective parent strains and in colonies of the other strain. Worker genotype and host-colony type affected foraging activity. Workers from the high strain fostered in low-strain colonies returned with pollen on 75.6% of total foraging trips, while workers from the high strain fostered in high-strain colonies returned with pollen on 53.5% of total trips. Workers from the low strain fostered in low-strain colonies returned with pollen on 34.8% of total foraging trips while workers from the low strain fostered in high-strain colonies returned with pollen on 2.6% of total trips. Similar results were obtained in a second experiment. We suggest that workers influence the behavior of their nestmates indirectly through their effects on the shared colony environment. The asymmetry seen in the response of workers from these strains to the two types of colony environments also suggests that these genotypes exhibit different norms of reaction. Offprint requests to: N.W. Calderone     

Foraging behaviour of sympatric Antarctic and subantarctic fur seals: does their contrasting duration of lactation make a difference?

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.