Crested Terns. Courtship behaviour?

[Leo Berzins]

These Crested Terns walked around in a tight circle with their wings held out as shown. I thought this was probably some form of courtship behaviour. Is this right?

Any confirmation or other suggestions greatly appreciated.

[John Chardine]

You are right Leo, this is a courtship display. Terns tend to do this one or a variant at the early stages of pair formation. Note the exposed wrist joints on both birds, which is an indication of aggression (bird is showing intention to aggressively wing-flap). In early courtship, the male and female are unsure of each other and there is conflict between having to be close to your partner (for example for copulate) and the fear that this closeness causes. Remember males and females in a pair are two individuals that have likely not spent the winter together and may never have met if they are a new pair. Breeding requires that animals come within each other's "personal space" and many courtship behaviours function to wear down the fear that results from this. Once they get used to each other their courtship will not show so many aggressive elements.

Notice also here that the bird at the back is facing away from the other one- the bill is a major weapon in birds and females tend to be less aggressive in these interactions than males. One way to appease your potentially aggressive partner is to face away and not present the bill face on.

I'll try to find an example of a similar behaviour in the Common Tern and post later.

Many thanks for showing this. Anything to add anyone?

[Leo Berzins]

Thanks very much John for you detailed response. Most informative.

[John Chardine]

Here's an example from Common Terns. This species tends to bend over and stick its tail up in the air rather than stand upright like yours.