Another Bird Blog: Gatekeeper

Thursday, August 10, 2017

Gulf News

We get the impression that Linnets are not early risers. It can be half an hour after dawn before Linnets arrive in small parties at our Gulf Lane ringing site. Of course we don’t know where they all spend the night but it looks like there is no large roost, at least not at this time of year. As the autumn and winter progress, things may well change.

This morning I arranged to meet Andy and Bryan at 0600. Within five minutes the first Linnets began to arrive in parties of from 5 to 15 birds. Comings and goings continued until 11.30 when we called it a morning by which time we had ringed 37 Linnet arriving to feed in the wildflower and bird seed crop.

Early Start

Ringing Linnets provides information essential to their conservation. Ringing allows us to investigate the cause of changes in the population of Linnets. For their population to be stable and to preferably increase from current lows, the production of new breeding adults, which is dependent on breeding success and survival of immature birds, must balance or outweigh losses due to mortality. For effective conservation we need to know why the Linnet population is changing. Marking birds as individuals is the only way that survival rates can be estimated and therefore is an essential part of bird conservation. This is especially so for a Red Listed species like Linnet.

Linnet

We processed 37 Linnets in 5 hours. A breakdown of the individuals showed 5 adults (3 female, 2 male) and 32 juvenile/first years (19 male and 13 female). Added to the 49 ringed on Saturday last that is 86 Linnets ringed this week, a figure which rather begs the question of how many Linnets pass through this site in the course of a day or week?

“Processing” each Linnet involves a number of steps where we collect information. As experienced bird ringers we each have a long-standing principle of processing a bird as quickly as possible. This is based upon the premise that the bird’s welfare always comes first. In the course of each ringing session we collect basic data that combined with past, present and future data sets are used further along the line for analysis and scientific research.

Ringing station

1) Firstly of course, and as obvious as that may sound, we identify the bird as to its species and note this on the working field sheet for later input to a computer system. A week or two later the same information is transferred to the central BTO database that holds records of all birds ringed in Britain.

Linnet

2) Once identified the bird is fitted with the correct ring size, in this case a Linnet requires an “A” size, and the letter/number combination fitted is noted on the work sheet.

Linnet

3) We measure the wing length according to whether the ringer is left or right handed. Wing length is very often a clue as to the sex of the bird being processed. In many species, especially passerines, the wing length of a male is greater than that of a female. Where both sexes are alike e.g. Meadow Pipit, the wing length can help decide the sex of the bird, but this is never the deciding factor of ageing.

The wing length of a Linnet is within a quite tight range whereby it is the plumage differences throughout the year that determine a Linnet’s sex. In the case of Linnet, the wing length helps only to confirm the sex i.e. males are bigger than females. For the coming winter our own thoughts are that some of our winter Linnets may originate from Scotland and be recognisable as the forgotten Scottish race Linaria cannabina autochthona by their longer wings.

Linnet

4) We sex each Linnet according to well established criteria, mainly the amount of white in the 7th to 9th primary feather. In the spring and summer this process is made easier by the striking difference in male and female body plumage. The sex is noted on the field sheet next to the age.

Female Linnet

5) We check each Linnet and determine the amount if any of moult. If moult is present we note it on the working field sheet. Moult is a useful indicator of the health of a bird and its whereabouts in the yearly cycle of plumage change. Adult Linnets have a complete but staged moult of all their body and flight feathers during July to September. First year Linnets undergo a partial moult July to September. Of the five adult Linnets today, all were in active moult, a couple of them more advanced than others. Spotting the marked difference between old feathers and new feathers was very easy.

Adult Linnet moult

5) We weigh each Linnet to the nearest tenth of a gram. Weight can give an indication of the health of the bird. We combine the weight with an examination of whether or not the bird has visible fat and if so how much; the combination of the two may lead to the conclusion that the bird is storing fat in readiness for migration or during a cold spell. If fat is present we “score” it on the working field sheet alongside the weight. Normally, Linnets appear to carry little fat.

6) We note the time of weighing. A bird’s weight can change during the day so it is important to combine information about the weight with the actual time of day.

7) The bird is released. The whole process has taken a couple of minutes in which to collect a set of valuable information.

Bryan and Andy

Ringers' Manual

Ringing kept us pretty busy but we also managed to see other species this morning. In particular we noted 1 Marsh Harrier, 2 Kestrel, 2 Pied Wagtail, 6 Goldfinch, 3 Tree Sparrow and 2 Skylark.