Guard Stage Research Articles

Patterns of acceptance of artificial eggs and chicks by Magellanic Penguins (Spheniscus magellanicus)

Life history theory predicts that parents will not raise unrelated offspring. For seabirds, an ability to recognize their own eggs and chicks can prevent a costly mistake. We tested whether Magellanic Penguins (Spheniscus magellanicus) would discriminate against artificial eggs by presenting nine types of egg-objects and one type of artificial chick to penguins at their nests. Magellanic Penguins regardless of their sex or breeding status accepted all egg-objects. A generalized linear mixed model showed that mass and number of dimensions were the most important factors in predicting whether the object was accepted: flat egg-objects and light egg-objects were less likely to be incubated than round, normally weighted ones. We also tested whether Magellanic Penguins would retrieve egg-objects more frequently if the object was within 1 m of the nest cup. Penguins retrieved 75 % of objects that were 1 m from the nest cup, but only 25 % of objects that were 2 m from the nest cup. Lastly, we tested whether penguins would accept artificial chicks. We found that pairs with chicks less than 3 weeks of age (i.e., not out of the guard stage) were at least twice as likely to brood an artificial chick than pairs with chicks older than 3 weeks, pairs that had lost their chicks, or unmated males.

Does Corticosterone Affect Diving Behaviour of Male Adélie Penguins? A Preliminary Experimental Study

Abstract The amount of energy that organisms can allocate to self-maintenance and/ or reproduction largely depends on their foraging strategies. Because of corticosterone (CORT) involvement in the control of energy metabolism, food intake and locomotor activity, recent studies have sought to demonstrate the role of this hormone in foraging decisions and performance. Moreover, considerable recent advances in animalattached loggers now allow the study of behaviour in free-living animals. In order to assess the effects of CORT administration on the foraging behaviour of free-living Adelie Penguins Pygoscelis adeliae, we studied a group with CORT implants and a control group without CORT implants, by attaching time-depth recorders to the two groups and monitoring them throughout up to seven consecutive foraging trips during the guard stage (in Adelie Land, Antarctica). We found that foraging trips duration was similar between both groups. Dive durations, time spent at the bottom phase of dives, and the number...

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.

An observation of between-mates feeding behaviour in chick-guarding chinstrap penguins

Courtship feeding has not been reported for chinstrap penguins (Pygoscelis antarctica). However, we observed a male chinstrap penguin fed to his mate during the guard stage of chick. After being fed, the female regurgitated the food to her chick. Our observation suggests that the chicks’ behaviour of begging for food may be retained in adults, but it is usually restrained.

Diving behaviour of chick-rearing Adélie Penguins at Edmonson Point, Ross Sea

The diving behaviour of chick-rearing Adelie penguins of Edmonson Point, Ross Sea, was analysed over two summer seasons (1994–1995 and 1995–1996). In 1994–1995, the study area was characterized by fast-ice persistency throughout season and by higher pack ice concentration than the following year, when fast-ice retreated earlier. Both females’ and males’ behaviour were examined, and we then compared diving characteristic between years and between guard and creche stages of chick rearing. We found that changes in fast-ice extent influenced the transit times between colony and foraging grounds and that females conducted longer foraging trips, dived for longer periods and made more dives than males. The diving parameters were affected neither by the sex nor by the year, but differed between the breeding stages. Parents guarding chicks had longer dive and bottom phase durations than in creche (dive duration: guard = 48 s, creche = 42 s; bottom duration: guard = 34 s, creche = 26 s), whilst they had shorter recovery times (e.g. post dive duration) (guard = 29 s, creche = 32 s). Possible causes for the observed differences in diving behaviours are discussed.

Temporal variation in Adélie penguin diet at Béchervaise Island, east Antarctica and its relationship to reproductive performance

Diet, and in particular, food quality and quantity can influence the reproductive performance of marine predators. Also, the diet of specialist predators is often monitored in programmes that model and manage ecosystems. We examined the diet of Adelie penguins (Pygoscelis adeliae), an important consumer of Southern Ocean living resources, at Bechervaise Island, east Antarctica, during the chick-rearing periods for 11 years between 1991–1992 and 2002–2003. We also investigated the relationship between diet and annual reproductive performance. Substantial inter- and intra-annual variation in both meal mass and composition was evident: adults generally returned with larger food loads during the creche compared with the guard stages, and diet composition was dominated by two prey types, krill and fish, which combined contributed to >90% of the diet by mass in 7 out of 11 years. Females generally brought back meals dominated by krill; males generally consumed fish-dominated meals. However, both sexes returned with a high proportion of krill when annual mean meal mass was also high, suggesting that more food was available in high krill years. There was also evidence that years of high reproductive performance were positively correlated with years of both high meal and krill mass. We believe that our results indicate that there is significant long-term inter- and intra-annual variability in the amount of food available to Adelie penguins and that this was reflected in their diet and measures of reproductive performance. Coupled with the observation that penguins did not switch prey, this indicates that Adelie penguins from Bechervaise Island are dependent predators of krill. This contrasts with populations in other locations but supports the notion that Adelie penguins are an informative species to monitor the management of Southern Ocean marine living resources in this region.

Sex-specific parental strategies according to the sex of offspring in the Adélie penguin

In sexually dimorphic species, the sex of the offspring may induce different constraints for parents. At the same time, within pairs, males and females may have conflicting optimal reproductive strategies. As a result, they may adjust their level of parental investment differently according to the sex of the young. In this study, we examined whether Adélie penguin (Pygoscelis adeliae) chicks were sexually dimorphic and whether parents adjusted their parental investment accordingly. Male chicks were on average approximately 10% heavier than female chicks but not larger. Despite the presumed additional cost associated with male chick growth, no fitness cost differences were observed between parents rearing 1 chick whatever its sex: Adult body mass changes and resight rates during the subsequent breeding season were similar. However, the sex of offspring affected the duration of foraging trips during the early guard stage: At this stage, female adults rearing a female chick performed longer foraging trips than female adults rearing a male chick and males rearing either a male or a female chick. We propose that, because female adults present a lower survival rate after a breeding attempt, they are more prone to modify their level of parental investment than male adults. Moreover, the modulation of the foraging behavior by female adults according to the sex of the chick is likely to reduce intraspecific competition at a time when resource availability at sea is not optimal and when food requirement for female chicks may be lower than for male chicks.

SEA ICE COVER AND ITS INFLUENCE ON ADÉLIE PENGUIN REPRODUCTIVE PERFORMANCE

The relationship between Adélie Penguins (Pygoscelis adeliae) and ice is well established, with sea ice influencing penguin populations through a variety of processes operating at different spatial and temporal scales. To further explain the relationship between sea ice and Adélie Penguin reproductive performance, we investigated the relative importance of various measures of sea ice cover on breeding success at Béchervaise Island, East Antarctica. Our results show a clear distinction in the response of penguins to different types of ice, as well as to the timing of the presence of sea ice. Nearshore sea ice, which is composed primarily of fast ice during the guard stage of the breeding season, had an overwhelmingly strong and negative impact on penguin reproductive performance. The influence of winter and offshore guard-stage ice was only evident in conjunction with nearshore ice. Predicting Adélie Penguin population growth in relation to changes in the sea ice environment may be complicated because penguin-ice interactions vary according to the type of sea ice present, the season in which it is present, and the processes contributing to population growth that are influenced by sea ice.

Variability in foraging behaviour of chick-rearing macaroni penguins Eudyptes chrysolophus and its relation to diet

Flexibility in foraging behaviour and diet are characteristics of many penguin species. While these 2 aspects of foraging ecology are presumably tightly coupled, the connection between them is rarely examined directly. Using time-depth recorders and satellite telemetry we documented the foraging behaviour of 43 chick-rearing macaroni penguins Eudyptes chrysolophus at Heard Island. We also compared these behavioural data with prey recovered from the stomach contents of each tracked bird. During guard stage, foraging trips were significantly shorter (average duration = 23 ± 18 h, range = 47 ± 40 km) compared to creche stage (average duration = 115 ± 112 h, range = 169 ± 102 km). Creche stage trips also included significantly more shallow dives that appear to be related to travel (39% of dives <10 m versus 27% for guard stage). Three species dominate the birds' diet: 2 species of euphausiids and the myctophid fish Krefftichthys anderssoni. Over the breeding season, K. anderssoni was taken on trips further from the island with deeper dives compared to the euphausiids. Foraging characteristics also differed between trips targeting different euphausiid prey species; however, there was a temporal shift in the euphausiid species consumed and this was correlated with overall changes in foraging behaviour. Multivariate analysis of behavioural data from trips early in guard stage revealed 2 distinct foraging strategies: deeper and offshore versus shallower and inshore. Individual birds often switched between these strategies in successive trips. The characteristics of many dives performed during inshore trips were indicative of benthic foraging; a previously unrecorded behaviour for macaroni penguins. Euphausiids were captured on both offshore pelagic and inshore benthic trips, illustrating that when prey is found in different habitats substantial changes in foraging parameters can occur independent of dietary shifts. More detailed behavioural studies may allow prey-specific rather than habitat-specific foraging patterns to be distinguished. © Inter-Research 2008.

Activity-related variation in blood parameters associated with oxygen transport and chronic stress in little penguins

Some birds facing energy ‘bottlenecks’ display elevated oxidative metabolism and oxygen delivery to tissues and could be particularly susceptible to chronic stress. We examined whether there was evidence for such trends in little penguins (Eudyptula minor) over the period from breeding to the post-moulting stage and particularly during the onshore moult-fast. Penguin parents contribute equally to incubation, brooding and brood provisioning. A few weeks post-breeding, adults undergo a protracted, terrestrial moult-fast and then make brief visits to the colony during the post-moulting stage. Provisioning nestling(s) and moulting could theoretically be particularly energetically and nutritionally demanding. We determined for adults whether mass, a body condition index and blood parameters influencing vascular oxygen carrying capacity (hematocrit, Hct; whole blood haemoglobin, Hb) and indicating chronic stress (leukocyte count, WBC; heterophil/lymphocyte ratio, H/L) varied from August to May in a manner reflecting likely variation in energy and nutrient demand. Female mass and body condition index decreased significantly between the incubation and guard stages, before returning to incubation levels between the guard and post-guard nestling stages. Both parameters declined to their lowest levels between the post-guard and moult stages, before increasing to levels comparable with those during nestling care between the moult and post-moult stages. Blood parameters in both sexes exhibited temporal variation similar to that in female mass and body condition index, declining to their lowest levels during moult and increasing after the moult to levels comparable with those during breeding. Results indicated that the period of most intense provisioning of nestlings was associated with a decrease in blood oxygen carrying capacity, but no pronounced change in chronic stress indicators. However, the penguin’s moult-fast involved a loss of female body condition and, in both sexes, a reduction in body mass, vascular oxygen carrying capacity and possibly specific immune competence. Thus, regulation of human disturbance in accessible little penguin colonies may be particularly important during moult.

Long and Short Trips in Nonbreeding Buller's Albatrosses: Relationships with Colony Attendance and Body Mass

Abstract Foraging strategies of nonbreeding seabirds attending colonies remain virtually unknown. Here we report the results of a satellite telemetry study of nonbreeding Buller's Albatrosses (Thalassarche bulleri) from the Snares island group south of New Zealand in 2000–2001. Two 6- to 7-year-old prebreeding birds dispersed to Tasmania, Australia, from late May until at least late July. Six older birds (five prebreeding birds, one former breeding adult) all adopted a dual strategy of short trips (mean duration 1.3 days, mean foraging range 129 km) and long trips to southern New Zealand (9.6 days, 871 km) or Tasmania (22.0 days, 1918 km). Time allocation to short trips increased with age and experience (both sexes) and nest-site attendance (males), and decreased during the guard (when the chick is attended) and late postguard (chick left unattended) stages (females). Up to the guard stage, most birds present at their colony on consecutive days foraged overnight (mean foraging range 101 km). Nonbreeding birds used the same foraging areas as breeding adults, but allocated more foraging time to short trips during the corresponding incubation period and early postguard stage, and to long trips during the guard stage. Results suggest that prebreeding birds explore foraging areas sequentially, and increase their time ashore by progressing from making only long trips, to introducing short overnight trips, to modifying the duration of and allocation between long and short trips. Changes in body mass recorded on Solander Island (160 km north of the Snares) show that experienced nonbreeding birds initiate long foraging trips to regain mass lost during short trips, and suggest that less frequent short trips (and hence fewer returns ashore) among inexperienced birds are related to less efficient foraging during long trips.

Environmental conditions and life history constraints determine foraging range in breeding Adélie penguins

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 310:247-261 (2006) - doi:10.3354/meps310247 Environmental conditions and life history constraints determine foraging range in breeding Adélie penguins Judy Clarke1,*, Louise M. Emmerson1, Petr Otahal2 1Department of the Environment and Heritage, Australian Antarctic Division, 203 Channel Hwy, Kingston, Tasmania 7050, Australia 235 Seventh Ave, West Moonah, Tasmania 7009, Australia *Email: judy.clarke@bigpond.com ABSTRACT: Foraging movements of Adélie penguins are constrained both by environmental conditions (e.g. sea ice cover) and life history factors (e.g. regular offspring provisioning). We describe within season changes in foraging range, trip duration and body condition of Adélie penguins nesting at Béchervaise Island, East Antarctica, in the context of these constraints. Penguins were satellite tracked over multiple seasons during the incubation, guard, crèche and pre-moult phases of their annual cycle. They ranged farthest during incubation when sea ice was extensive and shortest during the guard stage when chicks were small and sea ice limited in extent. Prior to their annual moult the birds foraged hundreds of kilometres to the west and east of their breeding sites. A recurrent polynya facilitated access to the sea early in the season when ice cover was extensive. Kernel analyses showed that penguins foraged most intensively close to the colony, along submarine canyons and at the continental shelf break. Increases in foraging range, as the chick rearing period progressed, were consistent with changing energy requirements of adults and chicks and likely intraspecific competition. Whilst provisioning their offspring, penguins adopted a variable combination of time minimising and food maximising foraging behaviour in which choice of foraging rule was determined largely by adult body condition. KEY WORDS: Satellite tracking · Pygoscelis adeliae · Foraging range · Chick provisioning · Body condition · Kernel analysis · Polynya Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 310. Online publication date: April 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

LONG AND SHORT TRIPS IN NONBREEDING BULLER'S ALBATROSSES: RELATIONSHIPS WITH COLONY ATTENDANCE AND BODY MASS

Abstract Foraging strategies of nonbreeding seabirds attending colonies remain virtually unknown. Here we report the results of a satellite telemetry study of nonbreeding Buller's Albatrosses (Thalassarche bulleri) from the Snares island group south of New Zealand in 2000–2001. Two 6- to 7-year-old prebreeding birds dispersed to Tasmania, Australia, from late May until at least late July. Six older birds (five prebreeding birds, one former breeding adult) all adopted a dual strategy of short trips (mean duration 1.3 days, mean foraging range 129 km) and long trips to southern New Zealand (9.6 days, 871 km) or Tasmania (22.0 days, 1918 km). Time allocation to short trips increased with age and experience (both sexes) and nest-site attendance (males), and decreased during the guard (when the chick is attended) and late postguard (chick left unattended) stages (females). Up to the guard stage, most birds present at their colony on consecutive days foraged overnight (mean foraging range 101 km). Nonbreeding b...

Growth and survival of chicks in relation to nest attendance patterns of little penguins (Eudyptula minor) at Oamaru and Motuara Island, New Zealand

Little penguins breeding on Motuara Island, New Zealand, went on longer foraging trips during the incubation period compared with those breeding at Oamaru, Otago, resulting in higher rates of egg desertion at Motuara (Numata et al. 2000). In this paper, we report on the differences at these two sites in growth and survival of penguin chicks. During the guard stage at both study areas, parents alternated chick‐brooding duties on average every day, and lost 1–2% of their body mass after every trip. However, the duration of the guard stage was significantly shorter at Motuara (15.1 ± 1.0 days) than at Oamaru (20.0 ±1.0 days). Body condition of parents was poorer at Motuara than at Oamaru. The poorer food supply available to parents during chick rearing probably caused the lower growth rates and higher risks of desertion and starvation of chicks observed at Motuara.

BODY CONDITION AND PARENTAL DECISIONS IN THE SNOW PETREL (PAGODROMA NIVEA)

Abstract In Procellariiformes, parents guard the chick for some time after it has attained homeothermy. Such a strategy may have evolved to protect the chick from predation or inclement weather, but it is costly because only one parent can forage at a time. Therefore, the decision to leave the chick seems to be a trade-off between the chick's ability to care for itself, body condition of the parent present at the nest, and ability of the bird out foraging to return to the nest before its mate's body condition has degraded. We studied chick growth and survival together with number of days Snow Petrel (Pagodroma nivea) chicks were guarded before being left alone for the first time in relation to the parents body condition and ability to return to the nest in time. Parents in good body condition were more likely to produce a chick that survived the guard stage. They also guarded their chick for a longer period (range 2–8 days, x = 4.5) and finally left it alone with a higher body mass than those in poor bod...

Body Condition and Parental Decisions in the Snow Petrel (Pagodroma Nivea)

Abstract In Procellariiformes, parents guard the chick for some time after it has attained homeothermy. Such a strategy may have evolved to protect the chick from predation or inclement weather, but it is costly because only one parent can forage at a time. Therefore, the decision to leave the chick seems to be a trade-off between the chick's ability to care for itself, body condition of the parent present at the nest, and ability of the bird out foraging to return to the nest before its mate's body condition has degraded. We studied chick growth and survival together with number of days Snow Petrel (Pagodroma nivea) chicks were guarded before being left alone for the first time in relation to the parents body condition and ability to return to the nest in time. Parents in good body condition were more likely to produce a chick that survived the guard stage. They also guarded their chick for a longer period (range 2–8 days, x̄ = 4.5) and finally left it alone with a higher body mass than those in poor body condition. However, whether the foraging bird was able to return to the nest in time to relieve its mate was also strongly related to number of days the chick was guarded and its body mass. The chicks' survival from when they were left alone and until day 10 posthatch was positively related both to number of days they were guarded and their body condition (body mass corrected for age).

Survival analysis of Little PenguinEudyptula minorchicks on Motuara Island, New Zealand

Chick survival of Little PenguinsEudyptula minorwas studied on predator‐free Motuara Island, Cook Strait, New Zealand (41d̀05'S, 174d̀15'E), in 1995 and 1996. We used the Kaplan‐Meier estimator and robust Cox regression to estimate chick survival rate (pL se) at 0.325 pL 0.044, leading to an estimated survival from laying to fledging of 0.13 or a reproductive output of 0.26 chicks per pair and breeding attempt. Starvation posed the greatest mortality risk, followed by unknown factors and rain. Risk of death due to rain was restricted to the guard stage, whereas starvation occurred throughout the nesting period, though with a peak in the early guard stage. Significant seasonal differences in survival rate were detected in both years, but with reversed trends, survival decreasing with the season in 1995 and increasing in 1996. Failure of adults to relieve their partner on the nest after chicks hatched accounted for 16% mortality or 34% of all chick deaths. Differences in chick survival rate between nest types were significant in 1995, a year with high rainfall, but not in 1996. Nests in the base of hollow trees had the highest chick survival rate. Of chicks in open nests ‐ a nest type that is unusual for this species ‐ 5.4% fledged. Our results suggest that on Motuara Island good breeding sites are scarce and that the food supply has been poor during the years of this study.

Partitioning of foraging effort in Adélie penguins provisioning chicks at Béchervaise Island, Antarctica

Analyses of the body masses of Adelie penguins (Pygoscelis adeliae) departing on foraging trips of long and short duration (> and<40 h, respectively) during chick rearing showed that the departure weights of birds prior to long trips were significantly lighter than were those prior to short trips. Penguins, particularly males, were significantly heavier at the start of the guard stage than at the end and both sexes gained similar amounts of body mass during the creche period. Results support the hypothesis that the foraging effort of Adelie penguins at Bechervaise Island is partitioned between the sexes, with males accepting a net rate of negative energy gain to provide regular meals for their offspring during the guard stage. Adelie penguin foraging behaviour may be driven by a trade-off between the allocation of food to chicks and the storage of parental body reserves, similar to that previously postulated for some species of flying seabirds. The relevance of such a foraging strategy to the breeding success of penguins in the Mawson region of eastern Antarctica is discussed in relation to micronekton distribution in the area.

Benthic and pelagic dives: a new foraging behaviour in rockhopper penguins

The pattern and characteristics of diving of 55 daily foraging trips performed by 16 female southern rockhopper penguins Eudyptes chrysocome filholi were studied in coastal waters of Kerguelen Archipelago during the guard stage. Diving patterns and dive profiles indicated that birds used 2 foraging behaviours. First, they performed typical pelagic dives, as previously decribed for other penguin species. Second, they also performed series of consecutive square-wave dives reach- ing similar maximum depths, with no deeper dives within the series, all criteria which characterized benthic dives. Two groups of benthic and pelagic dives were subsequently selected to compare their parameters. In agreement with optimization concepts in foraging theory, rockhopper penguins max- imize bottom time (= feeding time) of benthic dives through an increase in both descent and ascent rates, thus minimizing transit time between the sea surface and the bottom. Regardless of dive depth, bottom time was longer and diving efficiency higher in benthic dives than in pelagic ones. Penguins were also more active during benthic dives, as indicated by higher numbers of depth and light wig- gles at the bottom of these dives. Bathymetry and dive depth indicate that penguins were able to reach about 80% of the sea floor surrounding the colony. Abrupt changes in dive depth within series of benthic dives were identical in height to the thickness of lava flows, the main geological features of the landscape, strongly suggesting that birds followed the bottom topography at a fine scale. Dietary analysis showed that rockhopper penguins fed upon benthic prey (a few fish and the mysid Mysidetes morbihanensis) and pelagic organisms, including the major item Euphausia vallentini. There was a positive linear relationship between the mass of food brought ashore and an index of the proportion of benthic dives during the daily trips, thus emphasizing the importance for rockhopper penguins living in a coastal marine environment of feeding on pelagic migrators trapped at or near the sea floor during the day.

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.