Swinhoe's Petrel Update

A Swinhoe’s Petrel was retrapped in the early hours of 9^th July during a petrelling session in the Havens. It was the second bird to have been caught here last year (i.e. the male which was retrapped on several occasions between early August and early September, the other bird was also a male, but was trapped only once, in July), so we’ll now be following the procedures agreed with the BTO and outlined here.
It was the sixth petrel-ringing session of the season and the first one that we’d played the full mix tape (the previous nights having all been quite light, so we decided to stick to just Storm Petrel calls to increase our chances of catching anything). It was the first really dark night and, after a total of 107 Storm Petrels ringed during the first five sessions, we ringed 47 last night; showing what a good night it was. There was also a Leach’s Petrel regularly singing around the nets (although skilfully avoiding them).
The phones have been pretty non-stop since 7am this morning with people wanting to know more about the bird (so not much chance for us to catch up on sleep!), so this seems a good a time as any to answer some of the questions we’ve been getting:

·      We shall not be playing Swinhoe’s calls during routine petrelling sessions from now on.

·      The Swinhoe’s Petrel calls we’ve been using have come from the excellent Petrels Night and Day book.

·       Owing to the vagaries of the Shetland weather we simply cannot advertise the days we’ll be Storm Petrel ringing in advance; we may be able to give an indication in the morning that we’ll be considering a session that night, in which case we’ll be happy to let people know what we’re thinking (but sessions can be cancelled right up until the last minute if there are changes in the weather or other unexpected circumstances).

·       We will not be ringing Storm Petrels either tonight or Thursday due to the forecasted weather conditions. No decision has been made on days beyond that.

·       There are no plans to fit any sort of tracking device to the bird. The advice we’ve received is that there are no tags small enough to remotely offload the data and that it is still very early days in the field of long-term attachments of tags to storm-petrels, so attempting to fit a tag to discover the winter movements of the bird would not be advisable. There wouldn’t be a huge amount of value to be gained from finding out its daily movements, given that it’s an out of range vagrant and isn’t breeding in the area.

The reason for the change in practice from our usual Storm Petrel ringing sessions is due to the unusual behaviour of this particular Swinhoe’s Petrel. The vast majority of petrels we catch are roaming birds that do not stay with us (we know from retraps etc that they are birds that are below the expected breeding age, whilst ringed birds from our breeding colonies are not caught in the nets in the Havens). This Swinhoe’s Petrel developed the habit last year of returning to the nets during every session and repeatedly in the same night on some occasions, unlike any of the other 3000 or so petrels we’ve caught in my previous three years on Fair Isle. We have no objection to people seeing the bird if we catch it (as I hope the folk who visited last year will agree) but feel it’s best for this bird if it is not repeatedly attracted to the nets.

Another factor to bear in mind this year is that is currently one of the best years for breeding seabirds in recent times. Last year’s almost total failure of several species meant we had more time to spend on Storm Petrel ringing, whereas that time is likely to be reduced this year due to the increased monitoring work, a very happy situation to be in!
It’s purely speculative at the moment, but one theory for this Swinhoe’s Petrels behaviour is that, whilst Storm and Leach’s Petrels roam between colonies as non-breeding birds (after spending their first summer further south than the UK) before eventually settling upon somewhere to breed at about four years old, this bird may be an adult that has been unable to locate another Swinhoe’s Petrel in the North Atlantic, hence its unusual behaviour. This perhaps lends a little support to the theory that UK Swinhoe’s Petrels are lost vagrants rather than part of a North Atlantic breeding population (one of the Tynemouth individuals returned for five years, suggesting it would have been at least six years old when last retrapped, by which time it probably should have been at a breeding colony).
Just to be clear, this is the first time that the Swinhoe’s Petrel has been seen (or heard) this year and we will be reporting any further sightings through the usual channels. If it does keep coming to the nets regularly despite Swinhoe’s Petrel calls not being played, we’ll review the procedures again.
I hope that this helps answer any questions people have got, if you do have any others though, please email me at fibo@btconnect.com (which is easier than me trying to keep abreast of all the goings on of social media).

Many thanks

David