May 2016

One good Tern deserves another

Could you please help me identify these birds? I know that they are Terns, but are they different species or the same?

Answer

Crested Tern (Thalasseus bergii) in breeding plumage Lesser Crested Tern (Thalasseus bengalensis) in early eclipse plumage

Tern identification can be difficult. Many species of Tern visit or reside in South-East Queensland, some are very similar in both appearance and behaviour. To make things even more interesting, this group of birds can occur in either breeding or non-breeding (also known as “eclipse”) plumage. This can vastly change the appearance of the bird. For the purpose of this discussion, we are only talking about adult birds.

The birds in your photographs appear to belong to two different species. One is a Crested Tern (Thalasseus bergii) in breeding plumage. The other is a Lesser Crested Tern (Thalasseus bengalensis) that may be in the early stage of moult into eclipse plumage (note the ‘dirty’ neck).

It is important to get a decent photograph for identification and you have done well in this regard.

Crested Tern in eclipse plumage; note the pale-yellow beak colour and the length of the tail relative to the wing-tips Lesser Crested Tern in breeding plumage; note the orange beak colour and more compact build

Here are our reasons for this identification:

      • Though it is easier to see when the two species are side by side; there is a size difference. Where this is most obvious is the size of the head and the wings proportionate to the body. The Crested Tern has a “Boofy” appearance due to the head and beak being quite large. The Lesser Crested Tern has a smaller head in comparison and on the whole, has a more compact and put-together appearance than the Crested Tern.
      • At rest, the wings of the Crested Tern are much longer than the tail and, in flight they are noticeably larger – when compared to the wings of a Lesser Crested Tern.
      • The other main feature is beak colour. The beak of a Crested Tern is a pale almost lemon yellow (though not quite that vibrant). The beak of a Lesser Crested Tern should be orange-yellow. Though this is mentioned in all of the field guides it isn’t always the best indicator. However in the case of your photographs the colour is consistent.

As demonstrated above it helps to focus on the basic characteristics of each species. Regardless of the phase of plumage (breeding or eclipse) that a bird is sporting, these features are fairly consistent and are significant contributors to the character or “jizz” of a bird.

Leg colour can also be a helpful character to note but, in the case of both species mentioned here, the legs are black. Both leg and beak colour can vary with breeding and non-breeding plumages.

Depending on your location in Australia, you can sometimes see between 5-8 species of Tern together at a time. Some of the other common Queensland species include the Caspian Tern (Hydroprogne caspia), Gull-billed Tern (Gelochelidon nilotica) and Whiskered Tern (Chlidonias hybridus) in wetland environments.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.