Yasuhiko Naito

Stroke and glide of wing-propelled divers: deep diving seabirds adjust surge frequency to buoyancy change with depth

In order to increase locomotor efficiency, breath–holding divers are expected to adjust their forward thrusts in relation to changes of buoyancy with depth. Wing propulsion during deep diving by Brünnichs guillemots (Uria lomvia) was measured in the wild by high–speed (32 Hz) sampling of surge (tail–to–head) and heave (ventral–to–dorsal) accelerations with bird–borne data loggers. At the start of descent, the birds produced frequent surges (3.2 Hz) during both the upstroke and the downstroke against buoyancy to attain a mean speed of 1.2–1.8 m s–1 that was close to the expected optimal swim speed. As they descended deeper, the birds decreased the frequency of surges to 2.4 Hz, relaying only on the downstroke. During their ascent, they stopped stroking at 18 m depth, after which the swim speed increased to 2.3 m s–1, possibly because of increasing buoyancy as air volumes expanded. This smooth change of surge frequency was achieved while maintaining a constant stroke duration (0.4–0.5 s), presumably allowing efficient muscle contraction.

VARIATION IN FORAGING AND PARENTAL BEHAVIOR OF KING CORMORANTS

Abstract We studied sexual and individual differences in foraging and parental behavior of King Cormorants (Phalacrocorax albiventer) during the brood-rearing period at Macquarie Island. King Cormorants exhibit sexual dimorphism in size, with males being 16% heavier than females. Females foraged mainly in the morning and males in the afternoon. Five females were shallow divers (1.9 to 6.8 m), and seven females were deep divers (19.6 to 28.0 m); males dived deeper (15.6 to 44.2 m) than both groups of females. The amount of time spent on the bottom (“bottom time”) relative to the dive cycle was higher for shallow-diving females (x̄ = 40 ± SD of 13%) than for males (x̄ = 26 ± 4%) and deep-diving females (x̄ = 27 ± 3%). Total daily dive time and bottom time per day did not differ significantly among groups because shallow-diving females dived more often (x̄ = 211 ± 81 dives per day) than males (x̄ = 68 ± 21) and deep-diving females (x̄ = 70 ± 7). Provisioning rate, trip duration, and proportion of time at sea did not differ significantly for males, deep-diving females, and shallow-diving females. Females, especially shallow divers, compensated for their shallow and short dives with more frequent dives. Consequently, male and female King Cormorants provisioned their chicks at similar rates despite large individual variation in foraging behavior.

Diving and foraging behaviour of Adélie penguins in areas with and without fast sea-ice

Abstract The diving and foraging behaviours of Adélie penguins, Pygoscelis adeliae, rearing chiks at Hukuro Cove, Lützow-Holm Bay, where the fast sea-ice remained throughout summer, were compared to those of penguins at Magnetic Island, Prydz Bay, where the fast sea-ice disappeared in early January. Parent penguins at Hukuro Cove made shallower (7.1–11.3 m) but longer (90–111 s) dives than those at Magnetic Island (22.9 m and 62 s). Dive duration correlated with dive depth at both colonies (r2 = 0.001 ∼ 0.90), but the penguins atg Hukuro Cove made longer dives for a given depth. Parents at Hukuro Cove made shorter foraging trips (8.1–14.4 h) with proportionally longer walking/swimming (diving < 1 m) travel time (27–40% of trip duration) and returned with smaller meals (253–293 g) than those at Magnetic Island, which foraged on average for 57.2 h, spent 2% of time walking/swimming ( < 1 m) travel, and with meals averaging 525 g. Trip duration at both colonies correlated to the total time spent diving. Trip duration at Hukuro Cove, but not at Magnetic Island, increased as walking/swimming ( < 1 m) travel time increased. These differences in foraging behaviour between colonies probably reflected differences in sea-ice cover and the availability of foraging sites.

Diving Performance of Adelie Penguins in Relation to Food Availability in Fast Sea-Ice Areas: Comparison between Years

Between-year variation in adelie penguin Pygoscelis adeliae foraging behaviour was studied using time-depth recorders at a colony in Lutzow-Holm Bay, Antarctica in the summers of 1990 and 1991 in areas where fast sea-ice remained. Poor chick survival and growth, long foraging trip duration and low meal delivery rate indicate that food availability was poor in 1991 when compared to 1990. However, mass of food brought to chicks per shore visit and rate of decrease of parental mass did not differ between these years. In 1991, the penguins on average dived deeper (12.3 ± 4.2m) and for longer durations (1.9 ± 0.2 min) than they did in 1990 (7.1 ± 1.6 m depth and 1.5 ± 0.2 min duration)

Penguin–mounted cameras glimpse underwater group behaviour

Marine birds and mammals spend most of their lives in the open ocean far from human observation, which makes obtaining information about their foraging behaviour difficult. Here, we show, by use of a miniaturized digital camera system, the first direct evidence (to our knowledge) of underwater group behaviour in free–ranging penguins. Penguins swim closely accompanied by other bird(s) during 24% of their possible foraging dives. This finding confirms that such miniaturized camera technology has broad applicability for advancing our knowledge about the previously unknown social interactions of marine animals at depth.

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

Abstract. 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 1xa0Hz, 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 40xa0m. The mean swim speed during non-feeding shallow and exploratory dives was relatively constant throughout the dive, around 2.1xa0m s–1, whereas during feeding deep dives, swim speed during the undulatory phase was lower (1.71xa0m 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.

A method for reconstructing three-dimensional dive profiles of marine mammals using geomagnetic intensity data: results from two lactating Weddell seals

The under-ice behavior of two free-ranging female Weddell seals (Leptonychotes weddellii) was studied using geomagnetic, acceleration and velocity sensors at Big Razorback Island in McMurdo Sound, Antarctica. The seals body angle and posture were calculated from the acceleration data and the heading from the geomagnetic intensity data. Together with swim speed, the seals three-dimensional underwater dive path, heading and even posture were reconstructed for each dive. Each instrument was deployed for 2xa0days, during which time these females made multiple, deep (≥50xa0m) dives, with average maximum depths of 236±27xa0m (n=4) and 244±121xa0m (n=40). Each seal appeared to choose a particular heading on which to descend. These headings were significantly different between seals and bouts (Watsons U2 test, P<0.05). These new instruments and methodologies are shown to provide valuable information on the fine-scale and complex movements of diving animals.

Why do macaroni penguins choose shallow body angles that result in longer descent and ascent durations

SUMMARY It is generally assumed that air-breathing aquatic animals always choose the shortest route to minimize duration for transit between the surface and foraging depth in order to maximize the proportion of time spent foraging. However, empirical data indicate that the body angles of some diving animals are rarely vertical during descent and ascent. Why do they choose shallower body angles that result in longer descent and ascent durations? To investigate this question, we attached acceleration data loggers to eight female macaroni penguins, breeding on the Kerguelen Islands (48°45′–50°00′S, 68°45′–70°58′E; South Indian Ocean), to record depth, two-dimensional acceleration (stroke cycle frequency and body angle) and temperature. We investigated how they controlled body angle and allocated their submerged time. The instrumented females performed multiple dives (N=6952) with a mean dive depth for each bird ranging from 24.5±28.5 m to 56.4±75.1 m. Mean body angles during descent and ascent were not vertical. There was large variation in mean descent and ascent angles for a given dive depth, which, in turn, caused large variation in descent and ascent duration. Body angles were significantly correlated with time spent at the bottom-phase of the dive. Birds that spent long periods at the bottom exhibited steep body angles during ascent and subsequent descent. By contrast, they adopted shallow body angles after they had short or no bottom phases. Our results suggest that macaroni penguins stay at the bottom longer after encountering a good prey patch and then travel to the surface at steep body angles. If they do not encounter prey, they discontinue the dive, without staying at the bottom, ascend at shallow body angles and descend at shallow body angles in a subsequent dive. A shallow body angle can increase the horizontal distance covered during a dive, contributing to the move into a more profitable area in the following dive. During the ascent, in particular, macaroni penguins stopped beating their flippers. The buoyantly gliding penguins can move horizontally with minimum stroking effort before reaching the surface.

Deep foraging dives in relation to the energy depletion of Weddell seal (Leptonychotes weddellii) mothers during lactation

Abstract. We examined the behavioral adaptations of Weddell seals (Leptonychotesweddellii) that may help them to compensate for decreasing energy stores during lactation. Field studies were conducted from late October to early December in 1999 and 2000 at breeding colonies in Antarctica. Data loggers were attached to adult females with pups aged 12–49xa0days old to record depth and temperature. Additionally, digital still cameras were also mounted on the mothers to monitor their behaviors and environment. The loggers were deployed on free-ranging seals (1999, n=11; 2000, n=30) for 16–62xa0h. Diving behavior varied markedly among individuals. Some seals did not dive below 50xa0m, while others spent more than 30% of their time repeatedly diving to depths greater than 50xa0m. The recorded images showed that seals sometimes stretched their necks to capture fish and other prey-like objects that were encountered near depths of 300xa0m. The percentage of the total time spent per day diving below 50xa0m was significantly correlated with date, pup age, and fatness (=girth/length) of the mother. Since thinner females spent a greater percentage of time in deep dives, we concluded that nursing Weddell seals adjust their diving behavior accordingly and dive deeper to feed on fish in order to replenish their own energy stores, which decrease during lactation.

Diving behavior of Adélie Penguins determined by time-depth recorder

The diving behavior of Ad6lie Penguins, Pygoscelis adeliae, was investigated near Syowa Station during December 1986, with time-depth recorders attached to nesting birds caring for 2to 3-week-old chicks. Three of four recorders were recovered 150-334 hr after attachment. Most (98%) of the 587 dives recorded were less than 20 m in depth and 40% occurred between 16:00 and 20:00. Mean depths ranged from 6.1-10.9 m and maximum depth was 16.9-26.8 m. Mean and maximum dive durations were 1.4-1.9 min and 2.7-4.0 min. Ninety-seven percent of dives occurred in 44 diving bouts that averaged 25.3 min and 12.9 dives per bout. Descent and ascent rates during dives were similar in 88% of dives, meaning that the penguins dived at low angles, averaging 5*.