Diving pattern and performance in relation to foraging ecology in the gentoo penguin, Pygoscelis papua

We present data on diving pattern and performance (dive depth, duration, frequency and organization during the foraging trip) in gentoo penguins Pygoscelis papua , obtained using time-depth recorders ( n = 9 birds, 99 foraging trips). These data are used to estimate various parameters of foraging activity, e.g. foraging range, prey capture rates, and are compared in relation to breeding chronology. Foraging trip duration was 6 h and 10 h, and trip frequency 1.0/day and 0.96/day, during the brooding and creche periods, respectively. Birds spent on average 52%of each foraging trip diving. Dive depth and duration were highly bimodal: shallow dives (< 21 m) averaged 4 m and 0.23 min, and deep dives (> 30 m) 80 m and 2.5 min, respectively. Birds spent on average 71%and 25%of total diving time in deep and shallow dives, respectively. For deep dives, dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals 2–3 times dive duration. We suggest that most shallow dives are searching/exploratory dives and most deep dives are feeding dives. Deep dives showed clear diel patterns averaging 40 m at dawn and dusk and 80–90 m at midday. Estimated foraging ranges were 2.3 km and 4.1 km during the brood and creche period, respectively. Foraging trip duration increased by 4 h between the brood and creche periods but total time spent in deep dives (i.e. time spent feeding) was the same (3 h). Of 99 foraging trips, 56%consisted of only one dive bout and 44%of 2–4 bouts delimited by extended surface intervals > 10 min. We suggest that this pattern of diving activity reflects variation in spatial distribution of prey rather than the effect of physiological constraints on diving ability.     

Diving patterns of female macaroni penguins breeding on Marion Island, South Africa

Despite the large biomass of macaroni penguins Eudyptes chrysolophus in the Southern Ocean, their feeding ecology is poorly known at some important breeding localities. We investigated the diving behaviour and diet of female macaroni penguins feeding small chicks on Marion Island (46o52′S, 37o5′E), South Africa, one of the species’ most northerly breeding sites, supporting 4% of their global population. We then compared our results with similar studies from other localities. In December 2008, we collected information on 12 foraging trips from 6 individuals using time-depth recorders, as well as diet from 42 individuals. Median trip duration was 22.8 h (5.6–80.8 h). Penguins performed 42.8 ± 15.9 dives per hour at sea, with dive depths averaging 24.6 ± 8.6 m and lasting 40.8 ± 12.1 s, although 74.3% of dives were <10 m. Euphasids dominated their diet (86% by mass), mainly Thysanoessa vicina. A second peak in dive depths at 55–80 m might reflect the 12% of fish in their diet. The substantial proportion of shallow night dives (30% of total dives) suggests some foraging occurs at night. Differences in diving patterns of individual macaroni penguins in this study confirmed the behavioural flexibility of these birds reported from other breeding localities. However, most other studies assumed that dives <3–5 m were commuting dives whereas our study suggests that at least some prey are caught during shallow dives. We highlight how different analytical methods can change the outcome of studies. Despite macaroni penguins’ apparent flexibility in foraging behaviour during the breeding season, their numbers are decreasing globally. Further investigations of their foraging behaviour are needed to assess potential competition with other predators and krill fisheries.     

Feeding strategies of free-ranging Adélie penguins Pygoscelis adeliae analysed by multiple data recording

The fine-scale feeding behaviour of free-ranging Adélie penguins (Pygoscelis adeliae) during a single foraging trip was investigated by monitoring three parameters simultaneously at a frequency of 1 Hz, these being depth, swim speed and oesophagus temperature. Ingestion events were detected as abrupt drops in the oesophageal temperature and related to the birds' foraging behaviour. Although a high percentage of oesophageal temperature loggers were rejected, 1 complete foraging trip was recorded for all the 3 parameters from 1 bird while 92% and 67% of the foraging trip was recorded for 2 other birds; 12.3% of the temperature drops occurred at the surface but they were mainly small, except 61 of them probably representing snow ingestion while the birds were on land. All other drops were observed during dives, 88% of them during the undulatory (and occasionally the ascent) phase of dives deeper than 40 m. The mean swim speed during non-feeding shallow and exploratory dives was relatively constant throughout the dive, around 2.1 m s^-1, whereas during feeding deep dives, swim speed during the undulatory phase was lower (1.71 m s^-1) than during the descent and ascent and was characterised by a series of rapid accelerations and decelerations; 42.6% of these accelerations were followed by one or more ingestion events and birds swam upward in 60% of the accelerations. Such multiple data recording opens new paths for the examination of the decision-making processes in foraging penguins.     

Satellite tracking and diving behaviour of sub-adult narwhals (<Emphasis Type="Italic">Monodon monoceros</Emphasis>) in Svalbard,Norway

Three juvenile narwhals captured during August 1998 in the northeast of Svalbard, Norway, were equipped with satellite-relayed data loggers (SRDLs) that transmitted diving and swim-speed data, in addition to location, for up to 46 days. A total of 1,354 complete dive cycles were recorded. Most of the diving was shallow and of short duration. Maximum recorded dive depth was 546 m, maximum recorded dive duration was 24.8 min, and maximum recorded swim-speed was 4.7 ms⁻¹. Ascent speed, vertical ascent speed, descent speed and vertical descent speed were all significantly higher during deep dives (>200 m) than for shallow dives (<200 m). In addition both ascent and descent angles were much steeper for deep dives than during shallow dives. Most of the shallow diving seemed to be associated with travelling, with the animal shifting between various locations, while the deep diving (often to the bottom) for extended periods in some specific areas might have been associated with foraging. Even though the sample size in this study is small, the data are the first information available for movements and diving behaviour of narwhals near Svalbard.     

Pursuit plunging by northern gannets (Sula bassana) feeding on capelin (Mallotus villosus)

Northern gannets (Sula bassana) are considered to obtain prey usually by rapid, vertical, shallow plunge dives. In order to test this contention and investigate underwater foraging behaviour, we attached two types of data-logging systems to 11 parental northern gannets at Funk Island in the North-Wiest Atlantic. We documented, for the first time to the authors' knowledge, gannets performing long, flat-bottomed, U-shaped dives that involved underwater wing propulsion as well as rapid, shallow, V-shaped dives. The median and maximum dive depths and durations were 4.6 and 22.0 m and 8 and 38 s, respectively. Short, shallow dives were usually V-shaped and dives deeper than 8 m and longer than 10 s were usually U-shaped, including a period at constant depth (varying between 4 and 28s with median 8s). Diving occurred throughout the daylight period and deepest dives were performed during late morning. On the basis of motion sensors in the loggers and food collections from telemetered birds, we concluded that extended, deep dives were directed at deep schools of capelin, a small pelagic fish, and we hypothesized that V-shaped dives were aimed at larger, pelagic fishes and squids. Furthermore, these V-shaped dives allowed the birds to surprise their pelagic prey and this may be critical because the maximum swimming speeds of the prey species may exceed the maximum dive speeds of the birds.     

Krill-feeding behaviour of gentoo penguins as shown by animal-borne camera loggers

Animal-borne camera loggers were used to examine the patterns of prey encounter and feeding behaviour of gentoo penguins at King George Island, Antarctica. The still images from the camera loggers showed that the penguins encountered the swarms of krill for 25.5% (range: 8–38%) of their dives (>5 m) on average, during their foraging trips (mean duration of 5.4 h, n = 7 trips). They encountered krill swarms during the dives to 10–70 m depth, in pelagic as well as benthic habitats. In the benthic habitat, the penguins swam just above the sea floor and headed downward over a krill swarm, probably using the sea floor to assist them to feed on mobile swarms. The shallow coastal waters would be the important foraging habitat of gentoo penguins breeding in King George Island.     

Effects of long-term implanted data loggers on macaroni penguins Eudyptes chrysolophus

We tested the hypothesis that implanted data loggers have no effect on the survival, breeding success and behaviour of macaroni penguins Eudyptes chrysolophus . Seventy penguins were implanted with heart rate data loggers (DLs) for periods of up to 15 months. When compared to control groups, implanted penguins showed no significant difference in over-wintering survival rates, arrival date and mass at the beginning of the breeding season. Later in the breeding season, implanted penguins showed no significant difference in the duration of their incubation foraging trip, breeding success, fledging mass of their chicks, date of arrival to moult and mass at the beginning of the moult fast. We conclude that implanted devices had no effects on the behaviour, breeding success and survival of this species. We contrast these results to those from studies using externally attached devices, which commonly affect the behaviour of penguins. We suggest that implanted devices should be considered as an alternative to externally attached devices in order to obtain the most accurate representation of the free-ranging behaviour, ecology and physiology of penguins.     

Diving behaviour and energetics in breeding little penguins (Eudyptula minor)

We present data on the diving behaviour and the energetics of breeding little penguins in Tasmania, Australia. Using an 18 m long still water canal in conjunction with respirometry, we determined the energy requirements while diving. Using electronic devices measuring dive depth or swimming speed, we investigated the foraging behaviour at sea. Cost of Transport was calculated to be minimal at the speed the birds prefer at sea (1.8 m/s) and averaged 11.1 J/kg/m (power requirements at that speed: 20.0 W/kg). Metabolic rate of little penguins resting in water was found to be 8.5 W/kg. The externally-attached devices had no significant influence on the energy expenditure.
Foraging trips can be divided into four distinct phases with different diving behaviours. A mean of 500 dives was executed per foraging trip lasting about 18 hours with 60% of this time being spent swimming. The total distance travelled averaged 73 km per day, although foraging range was about 12km. Mean swimming speed of little penguins at sea was 1.8 m/s, maximum swimming speed was 3.3 m/s. More than 50% of all dives had maxima not exceeding 2 m. Maximum depth reached was 27 m. Mean dive duration was 21 s. There were inter-sex differences in diving behaviour as well as changes in foraging behaviour over the breeding period. Aerobic dive limits (ADL) in the wild were estimated between 42 and 50 s. From the swim canal experiments we derived an ADL of 44 s. Total oxygen stores were calculated to be 45 ml O₂/kg. Only 2% of all dives exceeded the ADL. FMRs at sea were calculated to be between 1280 and 1500 kJ/kg/d according to chick size. The yearly food requirements of a breeding little penguin amount to 114 kg.     

Recording the free-living behaviour of small-bodied, shallow-diving animals with data loggers

1. Time-depth data recorders (TDRs) have been widely used to explore the behaviour of relatively large, deep divers. However, little is known about the dive behaviour of small, shallow divers such as semi-aquatic mammals. 2. We used high-resolution TDRs to record the diving behaviour of American mink Mustela vison (weight of individuals 580-1275 g) in rivers in Oxfordshire (UK) between December 2005 and March 2006. 3. Dives to > 0.2 m were measured in all individuals (n = 6). Modal dive depth and duration were 0.3 m and 10 s, respectively, although dives up to 3 m and 60 s in duration were recorded. Dive duration increased with dive depth. 4. Temperature data recorded by TDRs covaried with diving behaviour: they were relatively cold (modal temperature 4-6 degrees C across individuals) when mink were diving and relatively warm (modal temperature 24-36 degrees C across individuals) when mink were not diving. 5. Individuals differed hugely in their use of rivers, reflecting foraging plasticity across both terrestrial and aquatic environments. For some individuals there was < 1 dive per day while for others there was > 100 dives per day. 6. We have shown it is now possible to record the diving behaviour of small free-living animals that only dive a few tens of centimetres, opening up the way for a new range of TDR studies on shallow diving species.     

Diving in shallow water: the foraging ecology of darters (Aves: Anhingidae)

Diving birds have to overcome buoyancy, especially when diving in shallow water. Darters and anhingas (Anhingidae) are specialist shallow-water divers, with adaptations for reducing their buoyancy. Compared to closely-related cormorants (Phalacrocoracidae), darters have fully wettable plumage, smaller air sacs and denser bones. A previous study of darter diving behaviour reported no relationship between dive duration and water depth, contrary to optimal dive models. In this study I provide more extensive observations of African darters Anhinga melanogaster rufa diving in water<5 m deep at two sites. Dive duration increases with water depth at both sites, but the relationship is weak. Dives were longer than dives by cormorants in water of similar depth (max 108 s in water 2.5 m deep), with dives of up to 68 s observed in water<0.5 m deep. Initial dives in a bout were shorter than expected, possibly because their plumage was not fully saturated. Dive efficiency (dive:rest ratio) was 5–6, greater than cormorants (2.7±0.4 for 18 species) and other families of diving birds (average 0.2–4.3). Post-dive recovery periods increased with dive duration, but only slowly, resulting in a strong increase in efficiency with dive duration. All dives are likely to fall within the theoretical anaerobic dive limit. Foraging bouts were short (17.8±4.3 min) compared to cormorants, with birds spending 80±5% of time underwater. Darters take advantage of their low buoyancy to forage efficiently in shallow water, and their slow, stealthy dives are qualitatively different from those of other diving birds. However, they are forced to limit the duration of foraging bouts by increased thermoregulatory costs associated with wettable plumage.     

Southern rockhopper penguin Eudyptes chrysocome chrysocome foraging at Possession Island

The foraging ecology of rockhopper penguins was studied at Possession Island, southern Indian Ocean, by counting the number of birds departing from and arriving at colonies over the course of the day and by equipping three birds with time/depth loggers, one of which was recovered having recorded a total of 12 days foraging activity. Both the counts and the results from the diving behaviour showed that the birds foraged exclusively diurnally. Maximum dive depth was 66 m although most time was spent between 10 and 25 m, depths that did not accord with the published distribution of their principal prey as detected by nets and acoustics. Received: 29 March 1996/Accepted: 10 June 1996     

Foraging strategies of incubating and brooding king penguins Aptenodytes patagonicus

For oceanic birds like king penguins, a major constraint is the separation of foraging areas from the breeding colony, largely because swimming increases foraging costs. However, the relationship between foraging strategy and breeding stage has been poorly investigated. Using time-depth recorders, we studied the diving behaviour of two groups of king penguins that were either incubating or brooding chicks at Crozet Islands (Southern Indian Ocean) at the same period of the year. Although birds with chicks had the highest predicted energy demand, they made foraging trips half as long as incubating birds (6 vs. 14 days) and modified their time and depth utilisation. Birds with chicks dived deeper during daylight (mean maximum depth of 280 m vs. 205 m for those incubating). At night, birds with chicks spent twice as much time diving as those incubating, but birds at both stages never dived beyond 30 m. Movements to greater depths by brooding birds are consistent with the vertical distribution of myctophid fish which are the main prey. As chick provisioning limits trip duration, it is suggested that it is more efficient for parents to change their diving patterns rather than to restrict their foraging range. Received: 23 June 1997 / Accepted: 3 November 1997     

Extreme dives by free-ranging emperor penguins

We examined the incidence of extreme diving in a 3-year overwintering study of emperor penguins Aptenodytes forsteri in East Antarctica. We defined extreme dives as very deep (> 400 m) and/or very long (> 12 min). Of 137364 dives recorded by 93 penguins 264 dives reached depths > 400 m and 48 lasted > 12 min. Most (65%) very long dives occurred in winter (May–August) while 83% of the very deep dives took place in spring (September–November). The two most extreme dives (564 m depth, 21.8 min duration) were separate dives and were performed by different individual penguins. Penguins diving extremely deeply may have done so as part of their foraging strategy whereas penguins diving for very long times may have been forced to do so by changes in the sea-ice conditions.     

Group Size in Foraging African Penguins (Spheniscus demersus)

Diving synchrony was examined for varying group sizes of African penguins (Spheniscus demersus) travelling to their foraging grounds from their breeding islands. Groups of fewer than 12 birds always dived synchronously, whereas groups of more than 17 birds always dived asynchronously. Since travelling penguins do not dive deeply, large groups of birds can remain together irrespective of diving synchronization. Observations from boats showed that foraging penguins rarely occurred in groups of more than 17 birds. We suggest that groups of penguins that do not have synchronized dives cannot forage effectively, because foraging penguins dive deeply.     

Foraging ecology of Gentoo Penguins Pygoscelis papua at Macquarie Island during the period of chick care

The diet, diving behaviour, swimming velocity and foraging range of Gentoo Penguins Pygoscelis papua were studied at Macquarie Island during the breeding season in the 1993–1994 austral summer. Gentoo Penguins are considered to be inshore feeders, and at Macquarie Island the diet and estimated foraging ranges supported this. The diet consisted of 91.6% fish and 8.3% squid, by mass. The dominant prey taxa were the fish Gymnoscopelus sp. and Paranotothenia magellanica. A mixture of pelagic and benthic prey was consumed, with a greater proportion of benthic species occurring later in the season. The penguins exhibited a strong diurnal pattern in their diving behaviour. Deep diving (≥30 m) began near sunrise (03.00 h) and finished close to sunset (21.00 h). Diving at night was less common and very shallow (<10 m). Early in the breeding season, dive profiles indicated that birds were probably following vertically migrating pelagic prey through the water column and were foraging in waters over 100 m deep. Later in the season, more uniform, shallower depths were used, suggesting an increase in benthic foraging activity. These changes in dive pattern and depth were consistent with the habitat preferences of prey species found in the diet. Gentoo Penguins swam at 1.04 m per s and had a maximum potential foraging range of about 26 km for single-day trips. They tended to forage within 14 km of the colony, with a mean range of 5.4 km. This range encompassed the deep ocean habitat to the west and east of the island and a shallow area to the north.     

Time/depth usage of Adélie penguins: an approach based on dive angles

Data on the swim speed, dive depth and feeding rates of three Adélie penguins (Pygoscelis adeliae) foraging in summer 1998/1999 in Adélie Land, Antarctica were collected using dorsally-mounted loggers, in tandem with oesophageal temperature sensors. Swim speed could be integrated, together with the rate of change of depth, to determine dive and return-to-surface angles. Overall, birds increased rates of change of depth during commuting phases so that dive angles were steeper in dives terminating at greater depths. Angles of descent and ascent during feeding dives were greater than during non-feeding dives. Variation in the descent angle over time of particular dives was generally less than 10°, but the angles of the ascent phases varied more widely. The importance of selecting the optimum descent and ascent angles with respect to prey exploitation, oxygen stores and time gained in the feeding area over the course of a dive by diving at a steeper angle is discussed.     

Diving behaviour of Adélie penguins (Pygoscelis adeliae) at Dumont D'Urville, Antarctica: nocturnal patterns of diving and rapid adaptations to changes in sea-ice condition

The diving behaviour of Adélie penguins (Pygoscelis adeliae) was studied with time-depth recorders at Dumont D'Urville, Antarctica, during the breeding seasons in 1995/1996 and 1996/1997. We studied penguins foraging at all breeding stages, in various sea-ice conditions. For the first time in this species we observed nocturnal patterns of diving as the penguins dived more frequently and spent more time underwater around midnight than around noon. This behaviour may be related to the abundance of neritic krill, Euphausia crystallorophias, in the diet. Dive depth and duration varied extensively over the cycle, and appeared related to sea ice conditions rather than representative of the locality (22 m/78 s and 40 m/102 s with and without sea-ice, respectively). Comparisons with other studies showed that different diving behaviour previously observed in different localities can also occur at the same locality, and in some cases over a single foraging trip of a single penguin when short-term variation of external conditions occurred. Accepted: 27 September 1999     

Diving and haul-out patterns of walruses Odobenus rosmarus on Svalbard

Nine male walruses were equipped with dive recording devices in Svalbard to investigate walrus diving and haul-out behaviour in late summer. Dive information on 6,018 dives was collected by 3 satellite linked dive recorders. Additional dive information on 7,769 dives was obtained from 3 time depth recorders. The deepest dive recorded was 67 m, but mean depth of foraging dives was 22.5 m. The longest-lasting dive recorded was 24 min, but mean duration of foraging dives was 6 min. The walruses, on average, spent 56 h in the water followed by 20 h hauled out on land.     

Diving pattern and performance in the macaroni penguin Eudptes chrysolophus

The pattern and characteristics of diving in two female macaroni penguins Eudyptes chrysolophus was studied, during the brooding period, using continuous-recording time-depth recorders, for a total of I8 days (15 consecutive days) during which the depth, duration and timing of 4876 dives were recorded. Diving in the first 11 days was exclusively diurnal, averaging 244 dives on trips lasting 12 hours. Near the end of the brooding period trips were longer and included diving at night. About half of all trips (except those involving continuous night-time diving) was spent in diving and dive rate averaged 14–25 dives per hour (42 per hour at night). The duration of day time dives varied between trips, and averaged 1.4–1.7 min, with a subsequent surface interval of 0.5–0.9 min. Dive duration was significantly directly related to depth, the latter accounting for 53% of the variation. The average depths of daytime dives were 20–35 m (maximum depth 11 5 m). Dives at night were shorter (average duration 0.9 min) and much shallower (maximum 11 m); depth accounted for only 6% of the variation in duration. Estimates of potential prey capture rates (3–5 krill per dive; one krill every 17–20 s) are made. Daily weight changes in chicks were directly related to number of dives, but not to foraging trip duration nor time spent diving. Of the other species at the same site which live by diving to catch krill, gentoo penguins forage exclusively diurnally, making longer. deeper dives; Antarctic fur seals, which dive to similar depths as macaroni penguins, do so mainly at night.     

Dive bout organization in the Chinstrap penguin at seal island, antarctica

Diving behavior of 2 breeding Chinstrap penguins (Pygoscelis antarctica) was studied focusing first and primarily on dive bouts rather than dives themselves. Analysis of dive bout organization revealed (1) though there are differences between solitary dives and dive bouts in dive duration and dive depth, the first dives of dive bouts do not differ from solitary dives in the dive parameters, (2) mean dive duration during bout correlates positively to both mean dive depth during bout and mean surface interval during bout, while number of dives during bout negatively correlates to both cost (consumed energy) and duration of a dive cycle during bout. These findings suggest the following possibilities on foraging behavior of penguins: (1) their decision to repeat diving depends on the result of the first dive at a site, and the first dives of bouts would tend to be searching or evaluating dives though they would be also successful foraging dives, (2) they repeat diving at a foraging patch until foraging efficiency decrease to a threshold of diminishing returns.