Friday, 10 October 2008

The Pioneers- Birdwatch

Photo:Double-crested Cormorants on the Azores

I have recently written an article for Birdwatch about my personal views on the phenomenon of vagrancy. I asked for the acknowledgement section and references to go here because I feel a few things need a little more explanation.

In short, my view on vagrancy is as follows:

There are multiple factors which can contribute to a bird turning up out of range. These factors include weather, sickness, ship assistance, migration direction preference variation at the genetic level, reverse migration, human interference, interactions between different birds in natal and wintering areas and interactions between different birds during migration. A lot of the time we can only guess at the reasons that have caused the occurrence of any particular vagrant. Each rare bird probably has a unique and complex set of factors which have contributed to it's occurrence.

However within this complex migration 'circus' certain patterns and phenomena emerge. There are clearly effects which occur as a result of vagrancy which include the colonisation of remote islands and speciation processes on these remote islands. Also vagrants are capable of pioneering the establishment of new migration routes and new wintering grounds. Therefore they are a driving force behind the evolution of migration systems and of speciation. They are quite simply- extra-ordinary and fascinating.

There is another side to vagrancy too. That is the sheer indifference of evolutionary processes which are evident by the painful and often fatal consequences of birds that go outside their normal ranges. For some there are consequences which can lead to evolutionary changes. For the vast majority, all that awaits them is confusion, discomfort and very often death.

In a nutshell vagrancy is "a story of an apparent direction, purpose and plan, which seems to emerge from the directionless discomfort and confusion of individual organisms".

Such a wide view on what is clearly a very broad subject is inherently problematic. However the purpose of this article is an attempt at suggesting some broad principles over what is a complex subject. More so the purpose of this article is to encourage discussion and debate.

There are many people who have contributed to this article. I think it is fair to say, that very few of them completely agree with my view. Main criticisms include the following: the view is not based on empirical evidence and much of it is assumption and speculation. The sample numbers are far too small to make any conclusions from and there is very little in the way of specific examples in my text. There is little systematic ringing studies of vagrants to examine their movements to back up any claims. Generally vagrants are considered of having no or little conservation value and the status quo is that they are generally unimportant. Also vagrancy cannot be considered as an overall phenomenon because there is too great a difference between short distance vagrancy (e.g. a Crested Lark in the UK) and long distance vagrancy (say a Glaucous-winged Gull). There is also a major difference between what is going on with Yellow-browed Warblers and say a lone vagrant on Scilly. Additionally there are many other factors involved in the evolution of migration systems, species range and speciation which intergrade with vagrancy. I agree with all of these criticisms, in part but all I am suggesting is a hypothesis, formulated from observation and experience, which is subject to falsification. It is, after all, debate which is the engine for arriving at the answer.
Darryl Spittle has been instrumental in helping with this article and has pain stakingly picked up all sorts of ambiguous group selection and over speculative comments I have made in earlier drafts, some which I have corrected and some which I have retained to ignite a reaction. Darryl has been extremely critical and helpful- the best sort of help. Pierre-Andre Crochet made some extremely instructive and constructive critical remarks and holds doubts regarding the fundamental principles of a genetic underpinning to vagrancy. Sam Woods basically re-wrote the article, reigning in my tendency to use too many words to say a few things . Early drafts have also been examined and commented on by specialist birding literature editors.

In terms of influences there are several prominent migration, vagrancy and popular science writers which I have very much enjoyed reading. They do not necessarily share my views but have influenced my conclusions and suggestions, presented in this article. These include, in no particular order, P. Berthold, R. Dawkins, N. Elkins, J.G Gilroy, A. Lees, S.J Gould, A.J Helbig, K.Thorup, I.Newton, K.Vinicombe and T.Alerstam.

1 comment:

Darryl said...

I'm not sure I see the "apparent direction, purpose and plan" but I definitely see "directionless discomfort and confusion", but then I'm a 'glass half empty' kinda guy :-) Here's hoping for a few uncomfortable and confused organisms in the next week or so.