Movements in Adelie penguins foraging for chicks at Ardley Island, Antarctica; circles within spirals, wheels within wheels

Eighteen Adelie penguins Pygoscelis adeliae tending chicks at Ardley Island (62°13\u27S, 58°55\u27W), Antarctica during December 1991 and January 1992 were equipped with multiple channel data loggers recording swim heading, speed and dive depth. These parameters were then equated together using vectors to calculate the foraging tracks of the birds at sea as well as depth utilisation. The deepest dive recorded was 97m although most dives terminated within 70m. In accordance with previous studies, descent and ascent speed of diving birds increased with maximum dive depth and absolute time spent for the descent and ascent increased with maximum dive depth. The distance moved to the farthest point from the island was 35km although 70% of all time at sea was spent within 10km of the island (all birds considered together). Consideration of the fine scale features of bird movement indicated that three major patterns were apparent; (i) virtual straight line movement, (ii) a circular or spiralling movement where circles had diameters ranging between 20 and 200m and (iii) extensive movement without any substantial displacement. A travel index (total distance travelled during a specified time divided by the straight line distance covered during this time) showed that the three behaviours had very different values. The frequency of occurrence of particular travel index values followed a logarithmic decay with straight line travel (with indices around 1) accounting for ca. 35% of all movement at sea with greater deviations from a straight line course occurring less often. It is supposed that straight line travel serves displacement, highly localised movement reflects prey pursuit and that the circular or spiralling movement arises from birds seeking out prey using detection systems other than vision

Beyond rings on birds for determination of movements: Wither the archival tag?

Two methods for determining the movement of birds are discussed; Global Location Sensing (determination of position by consideration of day length and local timing of mid-day) and dead reckoning (calculation of routes by vectors). These are examined for their utility over a number of scales. Work conducted on penguins demonstrates that, although global location sensing is not subject to drift errors, its temporal and spatial resolution makes the system only applicable for large scale movements over at least tens of km. Dead reckoning, however, can be used over scales ranging from tens of kilometres to centimetres. Positions derived from dead reckoning are relatively more accurate the closer they are in time and distance to each other although drift over time can be problematic. The high temporal and spatial resolution of dead reckoning means that animal decisions leading to their movements can be determined and this is examined for penguins over a scales ranging from tens of kilometres to metres. Future work is likely to concentrate on small scale movements in 3 dimensions which, to date, cannot be resolved with other system

Reconstructing the past using futuristic developments: Trends and perspectives using logger technology on penguins

Over the last two decades there has been remarkable progress in the development of sensory systems coupled with loggers that have been attached to free-living marine animals. Increases in sensor resolution, sensor diversity and memory size have been coupled with decreases in unit size. Thus, the periods over which animals have been monitored have increased from hours to months while the sampling frequency has decreased from minutes or seconds to fractions of a second. Four main interrelated trends can be identified. Determination of; (1) animal position in three dimensions, (2) the characteristics of the environment in which the animals operate, (3) animal behaviour and (4) energy management. The elucidation of these trends in penguins is discussed and perspectives given with regard to what is expected in the future

Reconstructing the past using futuristic developments: trends and perspectives in logger technology for penguins

Over the last two decades there has been remarkable progress in the development of sensory systems coupled with loggers that have been attached to free-living marine animals. Increases in sensor resolution, sensor diversity and memory size have been coupled with decreases in unit size. Thus, the periods over which animals have been monitored have increased from hours to months while the sampling frequency has decreased from minutes or seconds to fractions of a second. Four main interrelated trends can be identified. Determination of; (1) animal position in three dimensions, (2) the characteristics of the environment in which the animals operate, (3) animal behaviour and (4) energy management. The elucidation of these trends in penguins is discussed and perspectives given with regard to what is expected in the future

Surface pauses in relation to dive duration in imperial cormorants; how much time for a breather?

Air-breathing animals diving to forage can optimize time underwater by diving with just enough oxygen for the projected performance underwater. By so doing they surface with minimal body oxygen levels, which leads to maximal rates of oxygen uptake. We examined whether imperial cormorants Phalacrocorax atriceps adhere to this by examining dive:pause ratios in birds diving for extended, continuous periods to constant depths, assuming that the oxygen used underwater was exactly replenished by the periods at the surface. Examination of the cumulative time spent in surface pauses relative to the cumulative time spent in diving showed that surface pauses increase according to a power curve function of time spent in the dive or water depth. In a simplistic model we considered the rate at which birds expended energy underwater to be constant and that the rate of oxygen replenishment during the surface pause was directly proportional to the oxygen deficit. We then worked out values for the rate constant for the surface pause before using this constant to examine bird body oxygen levels immediately pre- and post dive. The model predicted that imperial cormorants do not submerge with just enough oxygen to cover their projected dive performance but rather dive with substantial reserves, although these reserves decrease with increasing dive depth/duration. We speculate that these oxygen reserves may be used to enhance bird survival when rare events, such as the appearance of predators or discovery of large prey requiring extended handling time, occur. The form of the oxygen saturation curve over time at the surface means that the time costs for maintaining constant oxygen reserves become particularly onerous for long, deep dives, so the observed decrease in reserves with increasing dive duration is expected in animals benefiting by optimizing for time

Up-beat motion in swimming limbs: New insights into assessing movement of free-living marine vertebrates.

A new system is presented for assessing the movement of animal limbs including, after suitable calibration, quantification of limb stroke frequency and amplitude, which may be used to derive limb angular velocity and acceleration. The system is based on use of an archival unit logging data from a Hall sensor, itself set to sense magnetic-field strength at frequencies of up to 30 Hz. Typically, the Hall sensor is placed on the animal body adjacent to the limb being monitored, while a small magnet is glued to the limb. Changes in limb position result in variation of the magnetic-field strength perceived by the sensor. Captive trials were successfully performed on a harbour seal (Phoca vitulina), an Australian sea lion (Neophoca cinerea) and a hawksbill turtle (Eretmochelys imbricata), as well as on 18 free-living Magellanic penguins (Spheniscus magellanicus). The unit performed well in almost all cases, illustrating that stroke frequency was relatively invariant in any species tending, however, to be higher in smaller animals and showing that the primary variance was manifest in stroke amplitude. As an example of the utility of the system, the importance of buoyancy was demonstrated in the penguins, which had longer glide phases and lower flipper beat amplitudes at greater depths, because body air was compressed, which reduced upthrust. The small size of the system (ca. 25 g in air) makes it suitable for a wide range of marine vertebrates. Potential problems of system sensitivity, the suitability of particular recording frequencies and the value of appropriate calibration are discussed

The potential costs of flipper-bands to penguins

1. The published literature on the effects of flipper-bands on penguin ecology is reviewed. Six published studies show the following. 2. In Adélie Penguins Pygoscelis adeliae, flipper-bands directly damaged flippers, increased swimming costs by 24%, decreased survival in the first year after banding by 28%, and may have accelerated decline of a dwindling colony by 3%. 3. Adult return rates to colonies among flipper-banded Adélie, Chinstrap P. antarctica and Gentoo P. papua Penguins decreased by 8%, 12% and 25%, respectively, between singleand double-banded penguins. Juvenile return rates among Gentoo Penguins were reduced by 10·5%. Return rates to the colony among double-banded King Penguins Aptenodytes patagonicus were 31·3% and 6·7% lower than among single-banded birds in the first and second years after banding, respectively, and single flipper-banded birds showed annual survival rates 21·1% lower than those of birds fitted with subcutaneous transponders. 4. Among Royal Penguins Eudyptes schlegeli, there were no differences between chick growth, adult over-winter survival and fledging success between flipper-banded birds and birds fitted with transponders. 5. Adélie Penguin adult annual survival rates were lower among flipper-banded birds than among unbanded birds. 6. On the basis of dive profiles for Adélie Penguins, it is estimated that increased swimming costs of 5% reduce prey contact time by 10%, and of 24% reduce prey contact time by 48%. These estimated ‘knock-on’ or cumulative costs coupled with the survival and breeding costs shown by the majority of published field studies suggest that data collected on some flipper-banded populations are biased. 7. The advantages and disadvantages of an alternative long-term marking technique, subcutaneously implanted passively interrogated transponder tags, are discussed. Research projects currently testing transponders and flipper-bands worldwide are listed

The foraging behaviour of Chinstrap Penguins Pygoscelis antarctica at Ardley Island, Antarctica

The foraging behaviour of 20 Chinstrap Penguins Pygoscelis antarctica breeding at Ardley Island, King George Island, Antarctica was studied during the austral summers of 1991/2 and 1995/6 using stomach temperature loggers (to determine feeding patterns), depth recorders and multiple channel loggers. The multiple channel loggers recorded dive depth, swim speed and swim heading which could be integrated using vectors to determine the foraging tracks. Half the birds left the island to forage between 02h00 and 10h00. Mean time at sea was 10.6 h. Birds generally executed a looping type course with most individuals foraging within 20 km of the island. Maximum foraging range was 33.5 km. Maximum dive depth was 100.7 m although 80% of all dives had depth maxima less than 30 m. The following dive parameters were positively related to maximum depth reached during the dive: total dive duration, descent duration, duration at the bottom of the dive, ascent duration, descent angle, ascent angle, rate of change of depth during descent and rate of change of depth during ascent. Swim speed was unrelated to maximum dive depth and had mean values of 2.6, 2.5 and 2.2 m/s for the descent, bottom and ascent phases of the dive. The sequence of maximum depths reached in a dive series was not random, tending to be concentrated at a particular depth, irrespective of whether the penguins were feeding at that depth or not. Generally, sequential dives to a specific depth were abruptly terminated by a single dive to another depth which was characteristic in having no bottom phase and unusually steep descent and ascent angles. The maximum depth reached during this dive was then adhered to in the next dive sequence. There were peaks in feeding activity between 06h00 and 09h00 and 14h00 and 22h00. Although foraging effort and relative success decreased around midnight when light intensity was lowest, birds did dive up to 22 m at this time, considerably deeper than sympatric Adélie P. adeliae or Gentoo P. papua Penguins. These findings indicate that, in accordance with their small body size, Chinstrap Penguins forage inshore close to the surface during the chick-rearing phase. Apparent short-comings in the volume of water searched compared to sympatric congeners can be made good by intense diving activity during the period at sea, with no inter-bout rests, higher swim speeds and an apparent ability to be able to forage at lower light intensities which enables Chinstrap Penguins to forage better under twilight conditions

In depth studies of Magellanic foraging behavior: Can we estimate prey consumption by perturbations in the profile?

A new concept based on analysis of dive depth data was developed to help estimate prey consumption in ten free-ranging Magellanic penguins (Spheniscus magellanicus) that were brooding chicks. By simultaneously analysing the undulations in the dive depth profile (measured by time-depth recorders, TDRs) and beak opening (obtained from the recently developed intra-mandibular angle sensors, IMASEN), it was possible to determine the proportions of the undulations in the dive profile that resulted (or not) in prey capture. This methodology allowed the number of prey consumed to be estimated with a mean error of 10±6% using TDR data alone. If the mean mass of prey is known, then the overall mass of prey consumed per unit time can be determined. Additionally, the method allows estimation of the depth at which prey is taken and thus indicates how penguins exploit the water column. Due to its simplicity, the proposed methodology has applications for other Spheniscus penguin species and should be considered for other marine endotherm divers that show undulations in the dive depth profile