Sunday, February 27, 2011

There are currently nine accepted records of Frigatebird sp. on the Britain and Ireland list (although some of these refer to the same bird) along with two records of Magnificent Frigatebird and one record of Ascension Frigatebird. With a primarily southwesterly distribution of records it's probably a good idea to gen up on how to nail a Magnificent Frigatebird. Unfortunately frigatebirds can be tough (and sometimes impossible) to identify and chances are that views are going to be a relatively brief flyby (or of something taken into care exhausted). There are five species to contend with, all of which appear similar, but within each species there are a variety of different plumages (It was only in 1914 that it was realised that there are five species rather than two). Indeed frigatebirds are one of the few groups of seabirds that are sexually dimorphic in plumage as well as size. In Costa Rica we had a chance to get to grips with Magnificent Frigatebird.

An adult male Magnificent Frigatebird. Good views but really it's just seperated on range as adult male Ascension Frigatebirds basically look the same and are often considered impossible to seperate in the field. There were no pale brown wingbars above (thus separating male Great Frigatebird) but aberrant male Mag Frigs can also show this feature to complicate things further (c) Richard Brown

An adult female Mag Frig. Lets hope for one of these on Bardsey as we can actually identify this (given such belting views). The black head extends as a well defined V down the white upper breast. The black of the vent forms another V pointing towards that of the throat. There's an indistinct greyish collar, just visible here. The white tips to the axillaries form diagnostic wavy lines on the underwing (c) Richard Brown

A juvenile would also be do-able, assuming that, like this one, the diagnostic white lines on the axillaries had developed. These are retained in females and in males up to subadult stage (c) Richard Brown

But when BBRC are faced with my claim of Magnificent Frigatebird the plot thickens. There are several intermediate phases between the above photos and the amount of overlap with other species is considerable. Ultimately a good photo showing anything between a juvenile with white axillary lines and an adult female might be the only way to get a fly-by accepted.

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