Wednesday, 18 January 2017

Fairy Tern pair – will they mate, or won’t they?


Both Fairy and Little Terns have been successfully breeding on the Gippsland Lakes over the 2016-17 summer season. I have been fortunate to participate in monitoring of a breeding colony.

The breeding colony is a busy and noisy place with much behavioural activity to observe and photograph when the opportunity presents.

Courting is of course a crucial activity in the reproductive process. The following sequence of photos shows a male Fairy Tern attempting to mate with a female however on this occasion he was unsuccessful. The event as it unfolded is described in the text and photo captions.

The male Fairy Tern approaches a seemingly receptive female.

He is very vocal as he approaches from behind.

She crouches and he is right behind her, calling still.

At this point I am thinking they are going to mate any moment and I am ready to capture them in the act with the camera.

Then suddenly another bird arrives and interrupts the couple.
This bird has come with a fish?

Fairy Tern males often include fish gifts as part of their courtship and mating ritual. The fish is often wiped on the back of the female’s back, neck and head and just before, or at the moment of copulation, the fish is given to the female. However, in this case the amorous male does not have a fish to offer, though the female seemed receptive none the less.

The male’s momentum seems to have been disrupted by the arrival of another bird,
 possibly a male, with a fish. The female walks off – exit stage right?

The bird with the fish departs and the interrupted suiter follows and catches
up with the female. He looks to be trying to take up where he left off.
 
The female has lost interest and he has lost momentum,
the moment has passed and she walks off.
 
I felt sure he was going to mate with the female. He was in position and she seemed receptive. He called a lot and was close behind her for several minutes during which time it looked like he would mount her any second. Then when the other bird arrived the mating opportunity was lost even though there was a brief attempt to resume the encounter after the bird with the fish departed.

Fairy Terns lay between 1 and 3 eggs, usually 1 or 2. I wonder if the females are faithful to one mate or do they have several mates? Both male and female share in incubation and feeding of chicks so it seems they do pair bond. Therefore mating with multiple males is probably unlikely though some promiscuity would not be surprising in the highly charged atmosphere of a breeding colony.

Even cross breeding between Little and Fairy Terns is possible.