Why do our Bird Lists start with Swans and Geese? (2010 update)

When we go birdwatching, many of us like to make up a list of all the birds we see. It is easiest just to list the birds in the order in which we happen to see them. The trouble is, that makes it more difficult to compare lists seen on different trips, or written by different people. An obvious alternative is to list the species alphabetically. But it is better to try to group similar birds together, so that, for example a Chiffchaff is listed adjacent to a Willow Warbler. So, the ideal solution is to agree a standard sequence in which species of the same family are listed together, and then families that are closely related are listed together, and so on.

The lists of birds seen on our field trips are listed in a standard checklist sequence recommended by the British Ornithologists Union (BOU), and which they have recently revised. The general idea is that the most “primitive” families of birds appear at the beginning of the list and the more “highly evolved” families towards the end of the list. In the past, the sequence of birds in checklists was based on anatomical differences. However, in the past couple of decades, techniques based on studies of DNA (pioneered by Charles Sibley and co-workers) have told us much more about the genetic relationships between bird species. This has led to a reassessment of the most logical sequence for listing birds in field guides and in checklists. Since the scientific work is relatively recent, most of the field guides currently in use have not yet “caught up”, although some changes have been implemented in the recent second edition of the Collins Bird Guide.

In total there are over 10,000 species of birds. The passerines (Passeriformes) account for around 6,000 of these, while the rest belong to more primitive, non-passerine, orders. The most primitive orders of birds are the ratites and tinamous (these include birds such as ostriches and kiwis), but there aren’t any of those birds naturally resident in the UK. Next in line are waterfowl (Anseriformes) and gamebirds (Galliformes); these two orders constitute the next evolutionary split from all remaining birds. This does not necessarily imply that the Mute Swan is our most primitive bird, though there are some remarkably primitive birds (the screamers of South America) that belong to the same order. For the most part, the non-passerines are listed in the same sequence as in the previous version of the checklist, except that grebes have moved.

Most of the new changes affect sequence of passerines. The passerines are split into Sub-oscines and the Oscines (also sometimes referred to as songbirds). The sub-oscines’ stronghold is in the New World (e.g. tyrant flycatchers), and there are none resident in the UK. The main division of songbirds is into Corvida, including crows, orioles and shrikes, and Passerida. The Passerida are in turn divided into three main groups: Sylvioidea (including warblers, tits and swallows); Muscicapoidea (including nutchatches, starlings, wrens, flycatchers and thrushes) and lastly the Passeroidea (including accentors, sparrows, wagtails, finches and buntings). One thing to note is that within the family Mucipapidae, true thrushes are now assigned into one sub-family (Turdinae) while flycatchers and chats are now grouped together as Muscicapinae - which means that the Pied and Spotted Flycatchers now appear mixed up with robins and chats.

Is this checklist sequence the final word? It is fair to say that the overall picture of the relationships between orders is now clear, but there are still uncertainities in the relationships between different families and within families. For example, it is not clear where some families, such as the Regulidae (Goldcrest, Firecrest, etc.), should appear, so their position will eventually change. Expect more revisions to the checklist sequence in the future.

Richard Swinbank

17 September 2010

Reference: Sangster, G., Collinson, J.M., Knox, A.G., Parkin, D.T. and Svensson, L, 2010: “Taxonomic recommendations for British Birds: Sixth report.” Ibis 152: 180-186.