If you’ve never seen a baby tree sparrow’s leg, it’s little more than a pencil line. If it wasn’t attached to a feathery ball with a big yellow mouth, you might not even notice it.
Despite their size, these tiny limbs are able to be ringed when the youngster is just 7-9 days old. Which is what has been happening at Bempton Cliffs over the past couple of weeks.
Warden Dave Aitken explained why:
‘There has been a massive decline in the UK tree sparrow population which occurred during the late 1970s and early 1990s. Despite a recent increase, current numbers stand at fewer than 10% of those of the late sixties. Therefore it’s important that, now more than ever, we monitor the health of our colony.’
So what caused the dramatic crash in numbers? Lots of things ... hedgerow clearance, intensive farming, loss of old trees, turning old farm buildings into homes. They all took their toll on the humble tree sparrow. So much so, they are a Birds of Conservation Concern red listed species and have ‘Red Status’ in the RSPB’s conservation rating.
Ringing is a vital tool when it comes to investigating population declines; it provides conservationists with vital data such as movement, how long they live for, changes in population, and how faithful they are to a site and more. Over time, this data will help conservationists draw conclusions that may help the population get back to where it was decades ago.
It’s a delicate operation and is only carried out by licensed ringers who take extreme pains to carefully ring and handle the birds. Each ring carries a unique number which allows the bird to be monitored over time, though the bird must be recaptured in order to record the data.
To date, this season, 116 juvenile tree sparrow have been ringed from 23 nest boxes on the East Yorkshire nature reserve. And early indications are positive. It looks like it’s shaping up to be a good breeding season with second broods already being cared for and brood sizes averaging 4 chicks per pair. .
The smallest ring size, AA (and nothing like the batteries), weighs in at just 0.04 g which is less than a raindrop. Young tree sparrows have fairly chunky legs so take a B ring which is 2.88mm in diameter and weighs fractionally more. Once in place, it has no effect on the bird’s movements - it’s a bit like us carrying a mobile phone around.
From here on in, a monitoring team will check up on the birds at regular intervals. So will the good start to the breeding season continue? Only time, and ringing data, will tell.
Images: Mark Thomas