Classification of birds
A comparison of different world lists
I wanted to organise my bird photos and thought I would separate them into their families. With this in mind, I went to the British Trust for Ornithology (BTO) website for a list of bird families. According to BTO, there are 9,845 living species of birds in 172 families in 28 Orders. This list also gives the number of species within a family that are found in the UK. Looking for more information, I followed the link to the Taxonomy in Flux checklist and discovered disagreement between the two lists. The Taxonomy in Flux site suggests that there are 248 families in 46 orders, quite a big difference from the BTO numbers. On further investigation, I found that there are four main world checklists.
They are:
- Clements, Aug 2019, (eBird) — 41 Orders, 249 Families and 10,721 Species (or 248 F, 10,562 S)
- BirdLife International (BirdLife) / Handbook of the Birds of the World (HBW), Vn. 3, Nov 2018 — 36 Orders, 243 Families and 11,126 Species (or 242 F, 10,943 S)
- International Ornithology Committee (IOC) World Bird List, Vn. 9.2, June 2019 — 40 Orders, 250 Families, 2,320 Genera and 10,916 Species (or 249 F, 10,758 S)
- Howard & Moore Vn. 4.1, Aug 2018 — 0 Orders, 237 Families, 2349 Genera and 10,175 Species (or 235 F, 10,025 S)
The numbers in parenthesis exclude extinct birds. One family is included in the totals but all species within it are now extinct; this reduces the number of families by one.
The primary goals and taxonomic principles behind these lists differ slightly and this leads to some differences in the number of recognised species and also, in some cases, into which family a species is placed and the order under which a family is listed.
Does it really matter? For most of us, the answer is no. But, if you keep checklists and are interested in how many birds you have seen, you may get different totals depending on which list you are using.
Howard and Moore recognises the fewest number of species, 10,175 as against 11,126 extant species recognised by BirdLife. That is 951 less birds. However, that is just looking at the numbers and not comparing actual species.
Looking at the species in the two lists, I found that they have 9,645 species in common, which is just over 85%. There are 1,481 species (16%) recognised by BirdLife but not by Howard and Moore but only 530 (5%) recognised by Howard and Moore but not BirdLife. Comparing the species lists of all four, I found there are 9,053 species common to all.
One example of a species not recognised by all is the artic redpoll (Acanthis hornemanni). This is recognised as a separate species by all except BirdLife. This is not what you might expect as BirdLife recognises the most species.
English names in the four lists mostly match but, taking the example above, Clements calls the arctic redpoll the hoary redpoll.
Howard and Moore does not classify their birds families into orders but the other three do. At the Order level there are 42 distinct orders between them of which 35 are common to all three. Clements has 41 orders, IOC has 40, and BirdLife has 36.
Excluding extinct species, there are 258 families in total but none of the lists recognise them all. Even though Clements and IOC have close to the same number of families (248 and 249) there are three in IOC not listed in Clements and one in Clements not listed by IOC. Howard and Moore’s list only has 235 families and 7 of these are not included in any of the other lists.
The way the data is presented also varies between the lists. I found the IOC list the most difficult to use because the layout makes it impossible to sort the data. Clements’s layout allows sorting, gives an easy to see range and also gives the year of extinction where appropriate. The Howard and Moore spreadsheet has no highlighting and is not the easiest to read but includes the date that a species was first recorded. In terms of ease of use, BirdLife’s list allows you to filter on most things and also has colour coded species status. In such a large dataset, this makes it much easier to find just the data you want. However, it does not have any indication of range.
Here is a comparison of the orders with number of families and species for the first 3 lists mentioned above. Please note that even though the numbers match between the list they may not include the same families within an order or the same species within a family. The numbers below exclude extinct birds. The IOC also publish a comparison of their 9.2 list with other world lists, which can be downloaded from their website.
| # | Order | Clements (41 Orders) | HBW (36 Orders) | IOC (40 Orders) | |||
|---|---|---|---|---|---|---|---|
| Fam. | Sp. | Fam. | Sp. | Fam. | Sp. | ||
| 1 | Accipitriformes | 3 | 251 | 3 | 250 | 4 | 265 |
| 2 | Anseriformes | 3 | 169 | 3 | 169 | 3 | 170 |
| 3 | Apodiformes | NA | NA | NA | NA | 4 | 483 |
| 4 | Apterygiformes | 1 | 5 | NA | NA | 1 | 5 |
| 5 | Bucerotiformes | 4 | 71 | 3 | 72 | 4 | 73 |
| 6 | Caprimulgiformes | 8 | 595 | 8 | 595 | 4 | 121 |
| 7 | Cariamiformes | 1 | 2 | 1 | 2 | 1 | 2 |
| 8 | Casuariiformes | 1 | 4 | NA | NA | 1 | 4 |
| 9 | Cathartiformes | 1 | 7 | 1 | 7 | NA | NA |
| 10 | Charadriiformes | 19 | 372 | 19 | 374 | 19 | 376 |
| 11 | Ciconiiformes | 1 | 19 | 1 | 20 | 1 | 19 |
| 12 | Coliiformes | 1 | 6 | 1 | 6 | 1 | 6 |
| 13 | Columbiformes | 1 | 331 | 1 | 350 | 1 | 331 |
| 14 | Coraciiformes | 6 | 182 | 6 | 187 | 6 | 177 |
| 15 | Cuculiformes | 1 | 145 | 1 | 149 | 1 | 147 |
| 16 | Eurypygiformes | 2 | 2 | 2 | 2 | 2 | 2 |
| 17 | Falconiformes | 1 | 64 | 1 | 64 | 1 | 64 |
| 18 | Galbuliformes | 2 | 54 | NA | NA | NA | NA |
| 19 | Galliformes | 5 | 293 | 5 | 306 | 5 | 298 |
| 20 | Gaviiformes | 1 | 5 | 1 | 5 | 1 | 5 |
| 21 | Gruiformes | 6 | 167 | 5 | 167 | 6 | 168 |
| 22 | Leptosomiformes | 1 | 1 | 1 | 1 | 1 | 1 |
| 23 | Mesitornithiformes | 1 | 3 | 1 | 3 | 1 | 3 |
| 24 | Musophagiformes | 1 | 23 | 1 | 24 | 1 | 23 |
| 25 | Opisthocoformes | 1 | 1 | 1 | 1 | 1 | 1 |
| 26 | Otidiformes | 1 | 26 | 1 | 26 | 1 | 26 |
| 27 | Passeriformes | 140 | 6334 | 137 | 6578 | 141 | 6452 |
| 28 | Pelecaniformes | 5 | 108 | 5 | 109 | 5 | 111 |
| 29 | Phaethontiformes | 1 | 3 | 1 | 3 | 1 | 3 |
| 30 | Phoenicopteriformes | 1 | 6 | 1 | 6 | 1 | 6 |
| 31 | Piciformes | 7 | 377 | 9 | 483 | 9 | 444 |
| 32 | Podicipediformes | 1 | 19 | 1 | 20 | 1 | 20 |
| 33 | Procellariiformes | 4 | 135 | 4 | 142 | 4 | 143 |
| 34 | Psittaciformes | 4 | 369 | 3 | 397 | 4 | 381 |
| 35 | Pterocliformes | 1 | 16 | 1 | 16 | 1 | 16 |
| 36 | Rheiformes | 1 | 2 | NA | NA | 1 | 2 |
| 37 | Sphenisciformes | 1 | 18 | 1 | 18 | 1 | 18 |
| 38 | Strigiformes | 2 | 228 | 2 | 236 | 2 | 241 |
| 39 | Struthioniformes | 1 | 2 | 5 | 62 | 1 | 2 |
| 40 | Suliformes | 4 | 58 | 4 | 53 | 4 | 60 |
| 41 | Tinamiformes | 1 | 46 | 0 | 0 | 1 | 46 |
| 42 | Trogoniformes | 1 | 43 | 1 | 43 | 1 | 43 |
| # | Total | 248 | 10,562 | 242 | 10,943 | 249 | 10,758 |
I have created a pdf file with my comparison the four world lists. As well as the table of orders it also incudes comparison tables of all the families between the four lists. This can be downloaded below.