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Shearwaters' Olfaction: a comparative study of sensory ecology in the Mediterranean Sea and Atlantic Ocean

Final Report Summary - SOMA (Shearwaters' Olfaction: a comparative study of sensory ecology in the Mediterranean Sea and Atlantic Ocean)

Animals use their sensory abilities to perceive and exploit their environment, and to interact with conspecifics and other species. Sensory abilities are highly adapted to lifestyle and subjected to strong selection. The study of signals perceived and how these signals contribute to survival and fitness thus are a topic of primary importance to behavioural ecology. Nevertheless, some sensorial abilities in the past have been largely neglected in some orders of vertebrates, such as olfaction in birds, due to prejudices and incorrect assumptions. In contrast, recent studies are bringing new evidence that olfaction plays a fundamental role in the ecology of at least some bird species, especially petrels. The main objective of this project was to extensively investigate the olfactory ecology of petrels, providing decisive evidence on the adaptive and evolutive importance of the use of olfaction by a comparative approach. We explored how olfaction contributes to behaviours such as (a) foraging, (b) nest recognition and homing. For this purpose, we chose the example of Cory’s shearwaters (Calonectris diomedea) because of its presence in both the Mediterranean Sea and Atlantic Ocean, allowing the comparison between subspecies breeding in different environments. We investigated

(a) Many procellariiforms use olfactory cues to locate food patches over the seemingly featureless ocean surface. In particular, some of them are able to detect and are attracted by dimethylsulfide (DMS), a volatile compound naturally occurring over worldwide oceans in correspondence with productive feeding areas. However, current knowledge is restricted to sub-Antarctic species, and to only one study realized under natural conditions at sea. We investigated the response to DMS in parallel in two different environments in temperate waters, the Atlantic Ocean and the Mediterranean Sea. The employment of Cory’s shearwaters as models allows to answer to two main questions. First, to explore the response to DMS in the northern hemisphere, where emissions are dramatically lower compared to previously explored areas, to understand if the attractiveness to DMS is widespread in oceans worldwide. Second, the direct comparison of the response by the same species in different marine environments allow to detail how such response vary in relation to different ecological niches, an approach never used so far. To test whether these birds can detect and respond to DMS, we presented them with this substance in a Y-maze. Then, to determine if they use this molecule in natural conditions, we tested the response to DMS at sea. The number of birds that chose the DMS in the Y-maze and that were recruited at DMS-scented slicks at sea suggest that these shearwaters are attracted to DMS in both non-foraging and natural contexts. Our findings show that Cory’s shearwater is sensitive and attracted to DMS, evidencing that the sensitivity and attraction to DMS are actually widespread among petrel species and different marine environments, including temperate waters. Our study opens a worldwide perspective to previous hypotheses concerning the use of DMS as a cue for foraging, providing experimental basis to theoretical work.

(b) Olfactory cues have been shown to be important to homing petrels at night, but apparently those procellariiform species that also come back to the colony during the day are not impaired by smell deprivation. However, the nycthemeral distribution of homing, i.e. whether displaced birds released at night return to their burrow by night or during daylight, has never been investigated. To explore this question, we studied the homing behaviour of Cory’s shearwater in the only known population where these birds are active at the colony both during the day and the night. Here, we compared the nocturnal versus diurnal homing schedule of birds treated with zinc sulphate to induce a reversible but complete anosmia, to that of controls. Our results show that anosmic shearwaters were unable to home in the dark and were constrained to wait for the daylight to find their burrow again. Our results confirm that olfaction is the basic sensory input for homing by night even in a petrel species that is diurnally active at the colony.

Procellariiformes are well studied in their general ecology and behaviour, but research on their sensory ecology began only recently. This project represented an important contribution to the advancement of knowledge through a comprehensive experimental and comparative approach. Moreover, the choice of shearwaters as model species facilitated clear answers concerning the debated role of olfaction in orientation. In addition, the results of this study provide fundamental new information for conservation actions. In fact, rehabilitation of suitable islands for breeding must take in account the selection processes that lead birds to choose a particular island. Our results show that olfaction may be one of the clues leading to the choice.

This had been the first study on this topic to be carried out in the northern hemisphere, especially in the Mediterranean Sea, and a fortiori in the EU. Sensory ecology of petrels (and in birds, in general) is a rising field and until now only two research groups in the world have worked in this domain: the University of California, Davis, USA, and the Host Institution of this proposal, the CEFE-CNRS. The realization of this project strengthened this European group, enhancing EU scientific excellence and leadership in a field of growing concern. Moreover, the proposal included fieldwork and collaborations between different EU members, promoting the transfer of knowledge and the establishing of new scientific networks.

Main researcher of the project – Marie Curie fellow:
Dr Gaia Dell’Ariccia

Supervisor – Scientist in charge:
Dr Francesco Bonadonna
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