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内容記述 |
The large number of seabirds exploiting the Southern Ocean in relation to their status of potential competitors with human fisheries for key-species of commercial interests explain the prime importance of studies investigating the birds' feeding and foraging strategies. With this intention, progresses in the development of new technologies have allowed researchers to monitor the behaviour of animals while at sea using loggers that measure various parameters as a function of time.<br /> In the past three years, deploying the most advanced technological devices in an integrative approach, multiple data per individual were recorded at a high sampling rate on free-ranging Adelie and King penguins. Depth utilization and swim speed as parameters of the foraging effort displayed by birds, were principally investigated in tandem with the monitoring of the oesophageal temperature, this latest being used to detect the ingestion of cold ectothermic prey, indicated by precipitous drops in the internal temperature of the predator. Thus, fine-scale foraging events could be related to feeding events.<br /> Calibration experiments on captive penguins, handfed on land and swimming in an exhibit pool, showed that the upper the sensors in the oesophagus, the higher the detection rate. Moreover, the magnitude of the temperature drop increase with the mass fed and decrease with increasing frequency of ingestion. Deployed on free-ranging birds in tandem with swim speed and depth loggers, the oesophagus temperature recording gave precious indication about the depths at which prey were taken. In addition to the feeding behaviour, several foraging strategies that may enhance the prey detection and/or capture were also revealed.Based on these data obtained on free-ranging penguins, the potential way birds locate the patch of prey within a foraging trip, possibly using chemoreception during shallow diving activity, as well as an updating of the classification of the role of dives using their depth profile will be described. Some of the most striking strategies displayed by both Adelie and King Penguins will also be discussed in the present thesis, these being i) the optimization of the commuting phase of the dive cycle (22% of the prey catches were observed during the ascent of the dives of Adelie penguins); ii) the use of an upwardly focused hunting strategy that may be related to the detection of prey in the deep using a backlighting effect; iii) the modification in the dive angles in relation to a prey encounter (birds descending the water column with a steeper angle when prey have been encountered in the previous dive); and iv) the intra- and interspecific adaptation of the swim speed to the status of the dive (feeding or non-feeding) and the type of prey pursued: Indeed, Penguins swam at a speed that accords closely to the minimum cost of transport during non-feeding dives and during commuting phases. On the other hand, the encounter with a prey led to an evolution in the range of speed used (the hunting speed of Adelie decreased, that of Magellanic increased and that of King Penguins became erratic), which depend on both the energetic advantages the birds might receive and the rate at which they could process prey.<br /> Besides the optimization in the acquisition of food resources, the relevance of these adaptations to the reduction of the energy expended while foraging will be briefly evoked. The relevance of system for detection of prey intake, such as the oesophagus temperature recording, in tandem with other parameters to investigate the foraging behaviour and decision-making processes of free-ranging seabirds will be stated in a final conclusion. |
要旨・審査要旨 / Abstract, Screening Result (324.4 kB)
