Rapid increase in Adelie penguin populations in the Lutzow-Holm Bay area since the mid 1990s

The Adelie penguin, Pygoscelis adeliae, an important component of the Antarctic marine ecosystem, is closely associated with sea ice. Ten breeding populations along the Soya Coast of Lutzow-Holm Bay have been monitored since the 1960s by the Japanese Antarctic Research Expedition and shown to be increasing. In most colonies, small peaks of population increase were observed in the late 1980s with a rapid increase from the mid 1990s. Frequent sea ice break-ups in Lutzow-Holm Bay in the mid 1980s and since the late 1990s are thought to have induced the population increase through increased subadult survival and preferred prey availability. Population monitoring therefore needs to be continued carefully in relation to the environmental changes

Are stomach temperature recorders a useful tool for determining feeding activity?

Despite a number of limitations, stomach temperature recorders are still commonly used to determine feeding activity in free-ranging marine predators. In this regard, it is important to improve the detection rate of these systems by, for instance, increasing the probability that a cold prey touches the sensors. In the present study, we compared the detection rates and mass estimations of water and fish prey ingested by captive king penguins using a two-point temperature recorder (STL) and a single, but large, point recorder (SICUP). Prey items were of different masses (5-45 g) and delivered at different frequencies (high vs. low). Ingestions were recorded as precipitous drop followed by an exponential rise (PDER). Overall, 57.9, 56.0 and 70.0% of the ingestions were detected by the SICUP and the upper and lower sensors of the STL, respectively. Our study confirmed that employing two sensors improves the detection of prey ingestion, but the detection of very small prey items remains insufficient and prey items swallowed at short intervals are detected as cumulative ingestion events. Nonetheless, the total mass of food ingested can be estimated with more than 70% confidence

Subjectivity in bio-logging science: do logged data mislead?

Logging of data using animal-attached archival units (bio-logging) involves potential sources of subjectivity that are reviewed in the present paper. Subjectivity may be the result of technical limitations of which the selection of the correct sampling frequency is particularly critical. Mistakes or aberrant data can also result from transitory defaults in the loggers functioning. Similarly, the use of purpose-written software to pre-process logged data before analysis is another step during which substantial modification of the raw data can occur. Apart from technical limitations, bio-logging devices are also known to modify the behaviour of the animal studied. Finally, arbitrary conclusions can eventually be drawn out from the \u27visual\u27 analysis of logged-data. The second part of this review proposes a non-exhaustive list of precautions so as to enhance objectivity in bio-logging approach. Among these precautions, assessment of the impact that data-logger may have on the animal, appropriate calibrations (for example for transformation of the raw measurements into useable variables) and multi-data sampling are useful steps in bio-logging utilization

Diving angle of great cormorants

Seabirds can maximize the relative time spent at depths where prey occur by minimizing the commuting time taken to reach these depths. One way to achieve this goal is to modify dive angle, but there are few measures of dive-angle in free-foraging seabirds. In 2003, we monitored simultaneously the swimming speeds and diving depths of great cormorants (Phalacrocorax carbo) foraging off the Greenland coast, and used these data to reconstruct their descent angle. Both males and females dived on average 12 m. We suggest that birds are able to reduce their descent time for dives beyond this depth by performing pre-dive leaps that allow them to use the momentum of the fall to descend almost vertically and at great speeds. Such pre-dive leaps in shallower dives would be unsuitable because of the proximity of the seabed and the risk of startling prey. Finally, in contrast with deeper divers, descent angles were not steeper when undulations were observed in the depth profile of the previous dive, probably because birds feed on dispersed prey

Bio-logging science: sensing beyond the boundaries

Bio-logging has emerged as a tool in animal biology much as genomics has emerged as a tool in the study of cellular and organ function. Bio-logging is certain to increase in its importance and to influence the way we study events and processes that are beyond the usual boundaries of perception and that are remote from the observer. It is providing insights into the behaviour and function of organisms in environments that are hostile to the observer and in natural situations. In terms of the way that data are collected it has much in common with remote sensing and Earth observation. This includes post hoc analysis and interpretation of extensive data sets involving a low diversity of measured variables. Owing to the sparseness of data sets, practitioners need to develop better methods of applying the data to models of the organisms being studied. Although increasing technological sophistication is leading to collection of a greater diversity of variables, this also brings complications of interpreting multi-dimension data sets. Although it appears that technology currently constrains the type of biological questions that can be addressed, there is a danger that technological advancement could result in a loss of focus on hypothesis testing. There is evidence that the discipline of bio-logging is developing a substructure within which specialist teams of modellers, theoretical and field biologists, and engineers collaborate to address complex biological questions

Finding the balance: the effect of the position of external devices on little penguins

Many studies on the foraging behaviour of penguins rely on data collected with back-mounted data recorders, which can greatly affect the drag of swimming birds. In recent years, the size of devices has been minimised to reduce drag. In addition, devices have been positioned on the lower back of penguins to reduce the effect of the flow separation caused by the device on the penguinユs body. Nevertheless, a device placed on the lower back of penguins is further away from the centre of gravity which may make balancing and swimming difficult. In this study, we used accelerometers to measure and test quantitatively whether the heaving and surging acceleration (as a measure of imbalance) of penguins swimming through a winding channel was different when an external accelerometer was positioned on the lower back compared to the middle of the back (closer to the centre of gravity).Heaving acceleration was different only for two of the seven penguins when a device was placed on the lower back rather than the middle of the back. While the difference was statistically significant, it was too small (less than 1 m/s2) to indicate a difference in the swimming behaviour. Although surging acceleration was consistently different in all seven penguins, we suspect this measurement indicated differences in acceleration between two parts of the body (tail and middle back) rather than an effect in balance. Overall, it seems that the balance of little penguins is not greatly affect by positioning of a device. Nevertheless, further experiments with free-ranging penguins are needed to evaluate fully whether the positioning of a device can affect balance of a penguin swimming on the water surface or its buoyancy when diving in the water

Trophic Structure in a Seabird Host-Parasite Food Web: Insights from Stable Isotope Analyses

Ecological studies on food webs rarely include parasites, partly due to the complexity and dimensionality of host-parasite interaction networks. Multiple co-occurring parasites can show different feeding strategies and thus lead to complex and cryptic trophic relationships, which are often difficult to disentangle by traditional methods. We analyzed stable isotope ratios of C (13C/12C, δ13C) and N (15N/14N, δ15N) of host and ectoparasite tissues to investigate trophic structure in 4 co-occurring ectoparasites: three lice and one flea species, on two closely related and spatially segregated seabird hosts (Calonectris shearwaters). δ13C isotopic signatures confirmed feathers as the main food resource for the three lice species and blood for the flea species. All ectoparasite species showed a significant enrichment in δ15N relatively to the host tissue consumed (discrimination factors ranged from 2 to 5‰ depending on the species). Isotopic differences were consistent across multiple host-ectoparasite locations, despite of some geographic variability in baseline isotopic levels. Our findings illustrate the influence of both ectoparasite and host trophic ecology in the isotopic structuring of the Calonectris ectoparasite community. This study highlights the potential of stable isotope analyses in disentangling the nature and complexity of trophic relationships in symbiotic systems

Trophic Structure in a Seabird Host-Parasite Food Web: Insights from Stable Isotope Analyses

Ecological studies on food webs rarely include parasites, partly due to the complexity and dimensionality of host-parasite interaction networks. Multiple co-occurring parasites can show different feeding strategies and thus lead to complex and cryptic trophic relationships, which are often difficult to disentangle by traditional methods. We analyzed stable isotope ratios of C (13C/12C, δ13C) and N (15N/14N, δ15N) of host and ectoparasite tissues to investigate trophic structure in 4 co-occurring ectoparasites: three lice and one flea species, on two closely related and spatially segregated seabird hosts (Calonectris shearwaters). δ13C isotopic signatures confirmed feathers as the main food resource for the three lice species and blood for the flea species. All ectoparasite species showed a significant enrichment in δ15N relatively to the host tissue consumed (discrimination factors ranged from 2 to 5‰ depending on the species). Isotopic differences were consistent across multiple host-ectoparasite locations, despite of some geographic variability in baseline isotopic levels. Our findings illustrate the influence of both ectoparasite and host trophic ecology in the isotopic structuring of the Calonectris ectoparasite community. This study highlights the potential of stable isotope analyses in disentangling the nature and complexity of trophic relationships in symbiotic systems

Patterns of energy acquisition by penguins: benefits of alternating short and long foraging trips.

In some seabirds, foraging trips have been defined as either long or short, with the length of time spent traveling to the foraging area apparently a critical feature in determining foraging trip length. Using logger technology, together with complimentary data from published studies, we investigated traveling and foraging times in 18 free-living Adélie Penguins Pygoscelis adeliae, which were foraging for chicks. Most deep, foraging dives were distributed around the center of the foraging trip. This central tendency was particularly apparent if the cumulative amount of undulations in the depth profile (indicative of prey capture) was considered during deep dives; values started to increase before 20.9% and ceased after 67.2% of the dives had occurred. This concentration of the feeding activity in the middle of the foraging trip indicates that birds traveled to and from a prey patch whose location varied little over the birds' trips. These data form the basis for a simple model that uses traveling and foraging times together with projected rates of prey ingestion and chick and adult gastric emptying to determine that there are occasions when, to optimize rates of prey ingestion while at sea for both adults and chicks, birds should conduct foraging trips of bimodal lengths

Lip-reading in remote subjects: An attempt to quantify and separate ingestion, breathing and vocalisation in free-living animals

A new mandibular sensor is presented here based on the use of a Hall sensor, attached to one mandible, opposite a magnet, attached to the other mandible. Changes in sensor voltage, proportional to magnetic field strength, and thus inter-mandibular angle, are recorded in a logger. This system was tested on seven captive Adélie penguins (Pygoscelis adeliae) and three gentoo penguins (Pygoscelis papua) during: (1) feeding trials on land, where birds were given known quantities and types of food; and (2) trials in water where birds were allowed to swim and dive freely. In addition, six free-living Magellanic penguins (Spheniscus magellanicus) were equipped with the system for single foraging trips. Angular signatures were looked for in instances when both captive and free-living birds might open their beaks, and it was discovered that five major behaviours could be identified: ingestion, breathing, calling, head shaking and preening. Captive feeding trials showed that prey mass could be determined with reasonable accuracy (r 2=0.92), and there was some indication that prey type could be resolved if recording frequency were high enough. Vocalisations in Adélie penguins (arc calls) took <0.7 s for mean maximum beak angles of 4.2° (SD 1.3), and were distinguished by their relatively gradual change in beak angle and by their high degree of symmetry. Beak shakings were distinguishable by their short duration (multiple peaks of <0.5 s) and minimal maximum angle (<0.5°). Preening behaviour was apparent due to multiple decreasing peaks (angles <8°). Breathing could be subdivided into that during porpoising, where a characteristic double peak in beak angle was recorded, and that during normal surface rests between dives. During porpoising, only the primary peak (mean maximum beak angle 25.1°, SD 4.7) occurred when the bird was out of the water (mean maximum for second peak 5.9°, SD 4.1). During normal surface rests in free-living birds, breaths could be distinguished as a series of beak openings and closures, showing variation in amplitude and frequency according to an apparent recovery from the previous dive and preparation for the subsequent dive to come. The mandibular measuring system presented shows considerable promise for elucidating many hitherto intractable aspects of the behaviour of free-living animals