Note "Avian orders"

Among ornithologists there is no general agreement on the exact number and composition of avian orders. In the following list, the three most relevant sources on avian orders are compared with the avian orders recognised herein: 

Clements Checklist Birds of the World v2019

www.birds.cornell.edu/clementschecklist/overview-august-2019

HBW & BirdLife Int. digital checklist birds of the world v2019

www.datazone.birdlife.org/userfiles/file/Species/Taxonomy/HBW-BirdLife_Checklist_v4_Dec19.zip

bird-phylogeny.de


1.) Struthioniformes

2.) Rheiformes
3.) Apterygiformes

4.) Tinamiformes
5.) Casuariiformes
6.) Anseriformes
7.) Galliformes

8.) Podicipediformes
9.) Phoenicopteriformes
10.) Columbiformes
11.) Pterocliformes
12.) Mesitornithiformes
13.) Cuculiformes
14.) Musophagiformes
15.) Otidiformes
16.) Caprimulgiformes
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17.) Opisthocomiformes
18.) Gruiformes
19.) Charadriiformes
20.) Eurypygiformes
21.) Phaethontiformes
22.) Gaviiformes
23.) Sphenisciformes
24.) Procellariiformes
25.) Pelecaniformes
26.) Ciconiiformes
27.) Suliformes

28.) Accipitriformes
29.) Cathartiformes
30.) Strigiformes
31.) Coliiformes
32.) Leptosomiformes
33.) Trogoniformes
34.) Bucerotiformes
35.) Piciformes
36.) Galbuliformes
37.) Coraciiformes
38.) Cariamiformes
39.) Falconiformes
40.) Psittaciformes
41.) Passeriformes

1.) Struthioniformes

2.) Rheiformes

3.) Apterygiformes

4.) Tinamiformes

5.) Casuariiformes

6.) Anseriformes

7.) Galliformes

8.) Podicipediformes

9.) Phoenicopteriformes

10.) Columbiformes

11.) Pterocliformes

12.) Mesitornithiformes

13.) Cuculiformes

14.) Musophagiformes

15.) Otidiformes

16.) Caprimulgiformes

17.) Apodiformes

18.) Opisthocomiformes

19.) Gruiformes

20.) Charadriiformes

21.) Eurypygiformes

22.) Phaethontiformes

23.) Gaviiformes

24.) Sphenisciformes

25.) Procellariiformes

26.) Pelecaniformes

27.) Ciconiiformes

28.) Suliformes

29.) Accipitriformes

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30.) Strigiformes

31.) Coliiformes

32.) Leptosomiformes

33.) Trogoniformes

34.) Bucerotiformes

35.) Piciformes

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36.) Coraciiformes

37.) Cariamiformes

38.) Falconiformes

39.) Psittaciformes

40.) Passeriformes

1.) Struthioniformes

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2.) Anseriformes

3.) Galliformes

4.) Podicipediformes

5.) Phoenicopteriformes

6.) Columbiformes

7.) Pterocliformes

8.) Mesitornithiformes

9.) Cuculiformes

10.) Musophagiformes

11.) Otidiformes

12.) Caprimulgiformes

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13.) Opisthocomiformes

14.) Gruiformes

15.) Charadriiformes

16.) Eurypygiformes

17.) Phaethontiformes

18.) Gaviiformes

19.) Sphenisciformes

20.) Procellariiformes

21.) Pelecaniformes

22.) Ciconiiformes

23.) Suliformes

24.) Accipitriformes

25.) Cathartiformes

26.) Strigiformes

27.) Coliiformes

28.) Leptosomiformes

29.) Trogoniformes

30.) Bucerotiformes

31.) Piciformes

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32.) Coraciiformes

33.) Cariamiformes

34.) Falconiformes

35.) Psittaciformes

36.) Passeriformes

1.) Struthioniformes

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2.) Anseriformes

3.) Galliformes

4.) Podicipediformes

5.) Phoenicopteriformes

6.) Columbiformes

7.) Pterocliformes

8.) Mesitornithiformes

9.) Cuculiformes

10.) Musophagiformes

11.) Otidiformes

12.) Caprimulgiformes

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13.) Opisthocomiformes

14.) Gruiformes

15.) Charadriiformes

16.) Eurypygiformes

17.) Phaethontiformes

18.) Gaviiformes

19.) Sphenisciformes

20.) Procellariiformes

21.) Pelecaniformes

22.) Ciconiiformes

23.) Suliformes

24.) Accipitriformes

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25.) Strigiformes

26.) Coliiformes

27.) Leptosomiformes

28.) Trogoniformes

29.) Bucerotiformes

30.) Piciformes

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31.) Coraciiformes

32.) Cariamiformes

33.) Falconiformes

34.) Psittaciformes

35.) Passeriformes


A comparison of the ordinal systems outlined above shows that they differ from each other only with respect to seven orders. For this homepage, I decided to accept only those orders that are represented in each of these ordinal system, leaving a total of 35 orders. Although not explicitly mentioned, this approach has also been chosen by Kuhl et al. (2021). It should be borne in mind, however, that all currently recognized ordinal systems are based on tradition rather than science. Therefore, it might be worthwhile to envision an alternative system of avian orders that takes into account the supposed age of the orders. Although this would be an objective way to define avian orders, it would result in significant changes to the traditional taxonomy and thus is not recommended at the moment. The main argument against changing the traditional system is the fact that the estimated divergence times often differ significantly among authors, largely depending on the selection of fossils and the maximum age constraint set be the investigators. [Explanation: Divergence time estimates are based on molecular dating techniques, which in turn depend on reliable fossil calibrations (i.e. correctly dated and taxonomically correctly placed fossils, which is a very difficult task)]. 

Futuristic timetree in which all clades that are at least 52 million old are attributed ordinal status. Where the names of traditional orders have been retained, although they have been split into several orders, these names are represented in blue colour. The newly recognized orders are represented in green colour. The total number of the novel avian orders amounts to 50.