Our man (Andy Schofield) writes:
Juvenile Pitcairn Warbler (A Schofield)
Since my last blog post about Pitcairn Warblers was a little brief - as I had only just started the process of catching and colour ringing individuals - I thought now that I was two months into the project I would write a fuller and therefore hopefully more informative account of what it is we are trying to achieve and how that is carried out.
The main aim is to catch individuals, give them a unique colour ring combination so that these individuals can therefore be identified again once they are released and then gain valuable information in the process regarding their size, weight and moult patterns.
I soon realized that you firstly had to spend quite a long time watching Pitcairn Reed Warblers behavior to understand what they are doing day to day. This would at least mean I would know the best place to set up the mist net - something I had struggled with in the past.
Photo (R Adam)
The picture above shows a great place to intercept them as in the late afternoon and early mornings they switch their foraging behavior from the low dense vegetation, similar to a typical Reed Warbler, to them spend the majority of their time in the middle part of the day to feeding in the more mature bush and tree canopy where their behavior is more akin to Flycatchers.
Once a bird is caught and placed in a 'bird bag' (above) it can then start to be 'processed' through a series of biometric measurements and given its unique set of colour rings. The first thing I would do whilst the bird was still in the bag would be to weigh the individual using a very accurate spring pesola balance. All the birds I caught weighed between 20 and 28 grammes. The local Pitcairners would often gather round when they saw me processing a bird, as they found it fascinating what you could learn from a 'bird in the hand'. The next stage would be to secure the colour rings to the warbler's leg or 'tarsus'. Unlike metal rings that need to be closed with pliers these plastic rings can be slid onto the bird's leg with a small gadget called a 'shoe' and can then be closed up again by firmly pinching and rolling the ring closed. Once the bird is ringed I would continue to take the rest of its biometric data including wing length which involves using a specially designed ruler with an end stop on it which the birds 'elbow' is held against and then the primary feathers are laid flat against the face of the ruler. They can then be gently straightened out to get the length.
Other measurements that were taken included tarsus or leg length, basically from the knee to the ankle. I also measured the length of the bill on each bird, and the measurement from the tip of the bill to the back of the head which helps record skull size.
All these measurements are meticulously carried out and recorded and will form a pioneering dataset that has never been held before for this species, the more birds that are caught and processed the more information we can hopefully extract and become better informed on how we can better understand this incredibly rare and vulnerable single island endemic which has a global range of two square miles!
One of the most interesting things that a 'bird in the hand' can tell you is very difficult or almost impossible to see on a 'bird in the bush' is their moult regime. Despite feathers being tough they do discolour, wear out and become damaged. Owing to the fully grown feather being a lifeless structure, unlike our finger nails and hair which grow continuously, the worn feathers must be replaced through a natural process of 'moulting'. The old, worn feathers are loosened from their follicles and eventually pushed out by the new feathers growing below.
In many species, particularly small, perching birds, the first moult takes place in their first autumn and replaces the juvenile plumage with the 1st winter plumage. This is often a partial moult with head, body and wing covert features only being replaced. For some species, the 1st-winter plumage will be indistinguishable from the adult plumage, but for others there will be differences. For some species the differences remain for much longer as there can be several intermediate or immature plumages between the juvenile and adult plumages. For example, sea birds, such as gulls, can take up to 4 years to reach adulthood. Many species also have non-breeding and breeding plumages. These different plumages are often most noticeable in male birds, which have brighter colours (such as Greenfinch) or ornaments (such as Lapwing) to use in displays to attract females. Almost every time there is a change in a bird's plumage it will have undertaken some form of moult. Thee are occasions when the plumage changes without a moult and this arises from the feathers wearing. For example, the tips of the spotted winter plumage of the Starling wear to reveal fully the iridescent plumage, and the tips of the throat feathers of the male House Sparrow wear to reveal the black throat patch.
Moulting is costly, in terms of energy, for birds and so usually takes place when the bird is less stressed, for example, late in the summer after breeding is complete, the weather is still warm and there is still plenty of food to be found. Further, birds do not lose all their feathers at once or they would be cold and unable to fly. The moulting takes place over a period. Larger species taken longer to moult than smaller ones, for example, a Tit, such as a Coal Tit, may moult all its feathers over about six weeks, a Herring Gull may take six months, but an Eagle may take several years for a complete change of flight features. Also, the keratin needed to make feathers is less abundant in vegetation than in insects, so seed-eating birds usually take a couple of weeks longer to moult than in insect-eating birds.
Picture shows fault bars in the young feathers which can indicate periods of stress through the feathers development.
Some species that migrate after the breeding season have a complete moult before leaving for their wintering grounds (eg Chiffchaff), others moult whenthey arrive (eg Garden Warbler) and still others start their moult before migrating and then complete it on arrival.
Depending on species the large flight features of the wings and tail are moulted in a strategic sequence. Many species moult their primary wing feathers in a strict sequence, this sequence varies from species to species. Water birds, such as ducks however can shed all the wing feathers at once and remain flightless for several species.
Releasing a bird caught in the school grounds with Pitcairn's only current school pupil, Cushana
We hadn't known anything about one of the UK's rarest and range restricted species before we started this project and it is clear we have a lot to learn and understand about its ecology. It is an immense privilege to be able to initiate this research and see what the Pitcairn Reed Warbler can tell us.
If you would like to support the work that the RSPB carries out in the UK Oversea Territories an you would like your very own Pitcairn Reed Warbler now is your chance!
I have a very limited edition (approx. 200) of the pin badge illustrated below and for £5.00 you can have one of them too. http://www.ebay.co.uk/itm/262044514781?ru=http%3A%2F%2Fwww.ebay.co.uk%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D262044514781%26_rdc%3D1
We've been working with the UK's amazing Overseas Territories for almost 20 years, but are still only scratching the surface of understanding their wonderful wildlife. One of the most remote and little known Territory environments is found in the Pitcairn Islands, the last remaining British Territory in the Pacific. Home to the extremely friendly descendants of the Mutiny on the Bounty, the Territory is made up of one inhabited island (Pitcairn) and three uninhabited ones.
We have a longstanding programme underway to restore one of these off-islands (Henderson Island World Heritage Site), but were conscious that the environment of Pitcairn itself is in many ways less studied than that of its uninhabited neighbours. Staff members have spent ten days on Pitcairn in consultation with the local community in 2010 and 2012, but as far as we are aware almost no general terrestrial conservationists have spent more than a week or two on the island. No one therefore really has any idea how big or threatened the population of the unique local bird, the Pitcairn reed-warbler, is, several of the island's unique plant species may be down to just a few individuals, and what invertebrate species exist on this fertile volcanic pinnacle is an almost untouched world still awaiting exploration and discovery.
We've therefore sent our new Overseas Territories Officer, Andy Schofield, to Pitcairn for three months to work alongside the Pitcairners and try to answer some of these questions. We're very excited to see what he may find!T