Scientific monitoring is a core function of National Nature Reserves (NNRs). Bird monitoring undertaken here at East Dartmoor NNR aids management of the breeding bird assemblage which is one of the reasons the site is a Site of Special Scientific Interest (SSSI). Natural England has a duty to maintain and enhance the breeding bird assemblage within the reserve, and to be able to do this it is crucial to have accurate bird data.
Bird ringing is a means of identifying individual birds which can then be used to monitor survival rates and bird movements. UK Bird ringers are trained and registered through the British Trust for Ornithology (BTO) and it takes several years to become licensed – the vast majority undertake ringing on a volunteer basis. Bird ringing is not only placing rings on birds but a range of other information is collected as part of the process. Records are submitted into the BTO national database providing the data on which we can assess the state of our bird populations. More information on bird ringing can be found here https://www.bto.org/volunteer-surveys/ringing
Here at East Dartmoor ringing is carried out through our pied flycatcher nest box monitoring scheme and takes place during the breeding season. Detailed nest monitoring is carried out from the time the first egg is laid until all the chicks have fledged. In addition to ringing the brood of chicks, the adult male and female are also ringed and previously ringed birds are recaptured, which provides valuable information. For example pied fly catchers are African migrants, and monitoring when the date of first egg laid indicates how this birds are adapting to the challenges of climate change. Mist-netting is another method used to catch adult birds for ringing and the method is used here as a demonstration for public engagement. This year Devon Wildlife Trust’s Bovey Local Group had the opportunity to get up close to our woodland birds. The visit proved that familiar species become a cause for celebration when seen at close quarters.
Mist nets were set up on the morning of the ringing in an area near feeders. The birds fly into the nets, and are then promptly extracted by licensed bird ringers, placed into cotton bags and taken back to the ringing base. The dark interior of the cotton bags ensures the birds stay calm until they can be processed. The ringers will then attach a uniquely numbered lightweight metal ring to the bird’s leg, age and sex the bird, weigh and measure it, before releasing the bird. Many of the birds already have a ring from a previous capture, and these recaptures provide the most useful information.
During the inspection process birds are securely held in the ‘ringers grip’ with the neck between the fore fingers – in this way the handler has control and the bird is secure.
The identification skills of the ringers are needed to distinguish between similar species such as marsh and willow tit, and age and sex individuals using a range of criteria, such as tail shape and retention of juvenile feathers indicating the different moult strategies different species have. A leg check reveals if the bird has been previously caught and ring details noted. Historic records will show where and when individuals were ringed, which helps to build a picture of survival, productivity, dispersal and migration routes.
Ageing a bird is an important part of the information collected when ringing a bird. For blue tits, for example inspection of the primary coverts (the feathers on the wing above the primaries or flight feathers) is used to ascertain age. Blue tits will only undergo a partial moult in the year of fledging, and this means some of the juvenile primary coverts (which are greenish in colour) are retained until the following year. This contrast between the green primary coverts on a first year bird and the rest of the wing feathers which are blue is an ageing criteria that can be used to separate from an ‘adult’ which has blue primary coverts and where there is no contrast. For small passerine birds the exact age of an adult cannot be determined by plumage alone, however a bird ringed as a chick or juvenile can provide this information, which is why there is added value in ringing chicks.
Wing length is measured which can be useful to study growth, variation between geographically separated forms, sex differences, age or otherwise characterize individual birds.
Recording some key information before the birds are released – the birds are weighed and the length of their wing is recorded
Finally the bird is weighed – this indignity looks worse to the onlooker than to the bird. It is brief and in the darkness the birds stay calm. Weight can vary significantly across the day depending on the time of day, and can be an indicator of physiological condition.
After processing is completed the birds are free to go! At the discretion of the ringers participants were able to release individual birds. Birds are laid in the palm of the hand and then fly off at their own pace.
Over 50 birds were caught during the morning and the response of the observers was universally positive ‘absolutely fantastic’, ‘did not anticipate being able to be so close to the birds’ appreciate the different sizes of the birds now’. The nets were taken down, and the brief insight into the world of bird ringing comes to an end – until the next time…
By Linda Corkerton and Tim Frayling, Natural England