Tuesday, 21 April 2015

Shag Research On The Farnes

Alongside the regular monitoring work that our team of rangers undertake on the Farne Islands, various scientific research projects are also undertaken each year on the islands.  Currently, Liz Morgan, a student at University of Leeds is carrying out her PhD studies looking at the foraging behaviour of the islands’ seabirds.

“Seabirds can be key indicators of the health of our seas and as such it is vital to study and monitor their populations both locally and nationally.” says Liz. “I am studying seabird foraging ecology and am lucky enough to spend my summer months living and working out on the Farne Islands. I am interested in the levels of consistency seabirds’ show in how and where they find food.  Understanding what drives consistency and flexibility in birds’ behaviour will help us improve conservation management decisions and better understand how species/populations may respond to changes in their environment.

Pic2- Photo ©Pete Steward “You can get extremely close to birds on the Farnes which makes studying them a whole lot easier!”

“My research is focused on one species in particular, the European Shag (Phalacrocorax aristotelis). Shags feed on or close to the seabed, making several short-range trips per day in order to catch their prey. This makes them an ideal subject for our study as we can gather data on multiple trips from the same individuals. By fitting birds with bio-telemetry devices we are able to find out where the birds are going (GPS) and how deep they are diving (Time-Depth Recorders). Using this information we can then examine if certain individuals show repeatability in foraging behaviours i.e. do they have preferences in their feeding locations and/or tactics?

Pic1- photo credit: Liz Morgan. GPS and depth recorders are attached to the underside of the bird’s tail. The tags weigh less than 3% of bird’s body weight and are removed after 4-5 days so we can download the data.

The Farnes are a great study location because there are multiple shag colonies on the islands that are easily accessible. In addition, the birds are quite used to a human presence, which undoubtedly makes catching them and retrieving our devices much easier. Last year’s field season (2014) was incredibly successful. We deployed devices on 33 birds over three islands, Inner Farne, Staple and Brownsman. Thanks to some dedicated help from National Trust and Newcastle University staff members, we successfully retrieved all of our devices. A 100% return rate, which is pretty unusual in seabird telemetry studies, especially for shags.

Pic3 - Example of the kind of data we can gather from fitting telemetry devices to birds. This shows the tracks of 5 Shags breeding on the islands in 2014.

Looking at last year’s tracking data it seems some individuals might be more repeatable than others. We also noticed some interesting patterns in where birds from the inner and outer groups of islands were foraging: birds from the inner islands tended to forage close to the Northumberland coastline and made relatively shallow dives to around 15-20 m in depth, whereas birds from the outer islands tended to make deeper dives, some up to 30-40m.

I will be investigating these patterns in repeatability and spatial segregation in more detail over the next couple of years. Meanwhile we are planning to gather more data in 2015 and 2016, ideally from the same birds we tagged last year, so we can look at year-year variability in foraging patterns. We are also hoping to see if members of the same pair are foraging in similar areas, and to look in more detail at the diets of birds nesting on the inner and outer islands. Hopefully we will have more results to report soon.

For more information and to follow the progress of my project this year you can find me on twitter @ElalmoLiz "

If you want to visit the Farnes to see Shags for yourself, click on the Farne Islands link in the left hand column for visiting information.

Liz's work is funded by the Natural Environment Research Council, supervised by Prof. Keith Hamer and Dr Chris Hassall at Leeds University. Fieldwork on the Farne Islands is being carried out in collaboration with the National Trust and Dr Richard Bevan and Dr Chris Redfern at Newcastle University.

No comments:

Post a Comment