Methodology

1. Catching the birds

It is fair to say that this part of the project is not exactly rocket science.  All birds are caught in my parents’ garden at Eccles Road, Holt using two drop traps made from clothes horses with fruit cage netting stretched over them. This forms a cage that is propped up on a stick, to which a string is attached. The string leads into the house, either through the cat flap (back garden, cat not inconvenienced as no longer with us) or through a hole in the external wall which my Dad kindly drilled to allow me to trigger the trap on the coal bunker. Mum baits each trap daily with seed, suet and sultanas, and for 95% of the year the birds are able to take uninterrupted advantage. However, on the days that I’m ringing, should an unmarked bird wander under the trap, I pull the string and the trap drops down – I can then walk straight out of the house and extract it within seconds. This is a remarkably efficient way of targeting individual birds but remember that it can only be undertaken legally by licensed BTO bird ringers.

2. Ringing the birds

As with any bird caught by a ringer, each individual is fitted with a metal ring bearing a unique alpha-numeric combination which allows it to be identified if it is captured by other ringers or found dead; if you find a bird wearing a metal ring anywhere in Britain & Ireland, you can report it to the BTO online.

OYGM_dave_leech

Rings are read from the top of the bird’s left leg to the bottom of the right; this male is therefore Orange over Yellow, Metal over Green (OYMG). Photo: Dave Leech

All of the birds in the Holt Blackbird Project have the metal ring fitted on the right leg. In addition, each adult bird caught during the breeding season is fitted with three coloured plastic rings, two on the left and one on the right. either above or below the metal ring. As recruitment rates are low, due to a combination of mortality and emigration, I don’t colour-ring juveniles; I do fit a metal ring, as this generates reports from the public and other ringers which helps us determine survival rates during the birds’ first winter.

Many adults caught in autumn and winter will be transient birds, a mixture of locals from the woodlands and hedgerows around Holt, migrants from other parts of the country and even European birds (I have had winter-ringed individuals recovered in Denmark and Sweden the following spring). As they will all leave the town to breed, resighting is very unlikely so they too are fitted with a metal ring only.

Four rings might seem like a lot for an individual bird, but their combined weight  is just 0.3 grams; the birds themselves weigh 90-110 grams in the summer and up to 140 grams in the winter, so percentage-wise this a very small mass increase, less than the typical daily fluctuation in weight. It is vital that a sufficient number of rings are used to enable each individual to be identified uniquely and their progress followed without needing to recapture them.

Eight colours have been used in the project to date:

Red (R), Orange (O), Yellow (Y), Blue (B), Green (G), White (W ), Black (N), Brown (U)

Be aware that the metal ring can look silver, grey or even white depending on the light, but it stands out fairly well over short distances and you”ll soon get your eye in; using binoculars is a great help, even when birds are close. The selection of colours and their relative positions is unique to each bird; the same combination has never been used twice.

3. Reading colour rings

This project only exists thanks to the efforts of all the volunteer who submit their sightings to me. I would particularly like to acknowledge my Mum, Barbara, and Gill Burden, my most prolific HoBOs (Holt Blackbird Observers!), and regular contributors John & Carol Wagstaff, Peter & Sue Morrison, Tim & Irene Loseby and Maggie Wilcox, but I’m grateful to anyone who has sent even a single sighting – they all help!

By making a note of the birds that you see each day, you will help to build a detailed picture of Blackbird movements and longevity. Colour rings are read from the top of the birds’ left leg to the bottom of the right- this can be a bit confusing as if the bird is facing you, its left leg is on your right, but with a bit of practice it soon becomes second nature.  Remember the metal ring is always on the right leg, so you can use this to orientate yourself!

The bird in the hand pictured above has an orange ring above a yellow one on its left leg and a metal ring above a green ring on its right leg, so this would be recorded as Orange over Yellow, Metal over Green, or OYMG. He’s a local lad, initially caught as a juvenile on 7 October 2012, having hatched earlier that year. Having recruited to the breeding population, he was caught again on 21 April 2014 and his colour rings were added; he has been resighted regularly in the garden since. While I do try and maintain rigorous scientific standards throughout, there may be a slight tendency for birds that I think are going to be dominant (big, adult males) to be given the yellow and green colours of my beloved Norwich City, while potential subordinates receive the blue and white of the ‘other’ club.

Vegetation can make it more difficult to read the rings, as can poor light. This bird is Blue over Black, Green over Metal (BNGM). Photo: Maggie Wilcox

Vegetation can make it more difficult to read the rings, as can poor light. This bird is Blue over Black, Green over Metal (BNGM). Photo: Maggie Wilcox

Reading rings in the field can be a little more challenging than when they’re in the hand – not only are they mobile, but vegetation can obscure the rings, even on a lawn, as BNGM is demonstrating in the picture on the right. However, compared to the Blue Tits that were the focus of my first colour-ringing study, Blackbirds are pretty obliging, spending lots of time on the ground and being fairly approachable. You may be able to increase the chances of reading rings by placing a perch close to your feeding station, allowing  a better view of the legs.

 

 

 

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