Back in January an expert team that included WWT scientists headed out to Bulgaria to catch wild red-breasted geese in the wintering grounds for the first time.
The goal was to fit transmitters to a number of these endangered birds in order to track their movements. Until now these enigmatic geese have been a bit of a mystery and in order to understand why their numbers are plummeting (the population suffered a 50% decline at the start of the century) we need to know more about them – in particular, their feeding distribution, their roosting behaviour, and their migration routes.
Over the next few years, several different types of tag will be fitted to the birds. Some will last only a few months but record the birds positions many times each day – these will give lots of detailed information about how they use fields in Bulgaria.
Others will last several years but record locations just a few times per day – these will help clarify the birds’ migration routes and perhaps identify previously unknown wintering sites.
After we had caught birds in Bulgaria in January, the weather turned unseasonably mild and nearly all of the red-breasted geese headed north – just 200 remained in the country at the end of that month.
Colder weather in February saw 3,000 return, including one of the two tagged birds, enabling us to download the data using a radio aerial.
The tag records the bird’s position very accurately using GPS every four hours and has already revealed much useful information.
Although Durankulak and Shabla Lakes are the preferred roosts, geese will also roost on the sea – normally when there is intense hunting pressure around the lakes or when the lakes are completely frozen.
Our bird roosted on the sea on several nights, and on one occasion – seemingly drifted by the current overnight – was 7 km from shore by 4:00 am. It left Bulgaria on 15 January for an area of Romania 100 km to the north where it stayed for the next two weeks. (It returned to Durankulak on the same evening that we arrived there for our second catching trip!)
Unlike Bulgaria, where birds are restricted to a thin coastal strip, our bird used an area about 50 km inland in Romania, adjacent to the Danube River. It roosted on a very small lake, just 500 m long by 50 m wide, but on several nights it remained in the fields throughout darkness.
On 7 February, having fed in the fields by Durankulak in the afternoon, its next location was 130 km to the north, yet by 4:00 am the next morning it was again back on the sea off Durankulak. Perhaps an aborted attempt at migration as the weather warmed up?
The next day we could not find the bird and, like many of the red-breasts, it had presumably started its migration in earnest. The tag also contains an accelerometer, which records small movements in the bird (similar to the handset of video games).
This will enable us to determine how long it spent feeding, resting and flying each day and will provide yet more insights into the bird’s response to weather, hunting and other factors, and, for example, whether it continued feeding when it remained in the fields overnight.