|Foraging ecology, movements and abundance of an avian predator of mesopelagic prey: new and deeper insights using novel techniques and ideas|
CESAM Responsible researcher - José Pedro Granadeiro & Teresa Catry
Execution dates - 2012-04-01 - 2015-03-31 (36 Months)
Funding Entity - FCT
Total Funding - 124250 €
Proponent Institution - ISPA - Instituto Universitário, Lisboa
Universidade de AveiroUniversidade de LisboaParque Natural da Madeira
Seabirds have an ubiquitous global distribution and are major consumers in marine food webs. In the last decade, the development of tracking technologies has revealed the spectacular capabilities and performances of avian predators. Coupled with remotely sensed oceanographic data, with dietary and with demographic studies, this spatially-explicit research agenda has met enormous success and development. Because seabirds may be easier to monitor and to study than other constituents of the ecosystems they integrate, they are increasingly being used as indicators in fisheries and of the marine environment. Furthermore, because many seabirds are threatened, they attract conservation efforts and are taken into consideration when designing marine protected areas or when planning the ecosystem-based management of fisheries.
So far, almost all studies of movements and foraging ecology of seabirds have concerned epipelagic predators. With the exception of king penguins, no specialised predators of mesopelagic species have been considered in any detail. This happens because most such predators are small petrels which, despite their global abundance, are difficult to study for a variety reasons. Their stomach contents are often heavily digested, rendering identification based on morphology problematic. Devices used for tracking have, until now, been too heavy to deploy on these birds. And even the assessment of numbers, for basic demography studies, is problematic, due to their underground nesting habits.
Taking advantage of recent technological developments, we propose here to carry out the first detailed ecological study (with an emphasis on foraging ecology) of a flying predator of mesopelagic prey, the Bulwer's petrel Bulweria bulwerii. Bulwer's petrels (body mass: ca 100 g) have a wide distribution, encompassing subtropical and tropical waters of the Atlantic and the Pacific oceans. In the NE Atlantic, they nest in the Azores, Madeira, Canaries and Cape Verde islands. At Selvagens and particularly at Desertas (around Madeira) they are extremely abundant, but little is known on their ecology, despite some studies of their breeding behaviour. As far as it is known, Bulwer's petrels feed mostly on mesopelagic fish (particularly myctophids) and squid, but no detailed studies have been carried out in the Atlantic. Their foraging and migratory movements are completely unknown.
Myctophids and other small pelagic fishes and squids are extremely abundant in worldwide oceans and presumably play an important role in marine food webs. Because they are not commercially explored and because they are difficult to sample, comparatively little is known on their general ecology and distribution, particularly in the NE subtropical Atlantic. By studying a specialist predator of this type of organisms, this project will also provide insights into the distribution and availability of such pelagic prey.
DNA-based methods for dietary studies is a new and rapidly developing research field that promises to help crack many difficult traditional problems in this area. These methods have not yet been much used in birds, despite the obvious potential and some successful trials (REFS). Working in close collaboration with leading world experts in this area, we propose to, for the first time, use these techniques to further our knowledge on the diet of a pelagic seabird. Molecular methods will be compared with and complemented by data gathered using conventional techniques, as well as by stable isotope analyses and state-of-the-art analytical tools (including mixing models). This will both contribute to the general development and trial of molecular techniques used in avian taxa, as well as to gather a fine picture of the diets of Bulwer's petrels and their seasonal and geographic variation.
Bulwer's petrels will be tracked using new miniaturised GPS loggers available in the market. These new devices have never been used in such small seabirds. Tracking of migratory movements will use light based geolocators (GLS), which, again have only recently been miniaturised to a point allowing tracking of such small species.
Data on diet and on movements will be combined with chick-growth data and with remotely-sensed environmental data to understand the influence of oceanographic spatial and temporal variability, at several scales, on the availability of different prey types and on the fitness of our model pelagic predators. To get a broader perspective on these issues, data from our main study sites at Desertas and Selvagens will be compared to data from a tropical colony, at Raso (Cape Verde islands).
Another major innovation of the present project is the pioneering attempt to estimate the numbers of a small crevice-nesting petrel at a huge colony where accurate land-based counts have proved impossible (Bulwer's petrels at Desertas). We will use a combination of two novel methods for this effort. First, we will colour-dye a large number of petrels at the colony and attempt to resight them at sea, in a classical capture-recapture experiment never carried out in this type of context. Second, we will use tracking data and an existing data base of at sea densities (from ship-based transects) to model the overall (absolute) abundance of petrels in the sea around the study colony.