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Friday, January 05, 2007

Breeding ecology of the Little Tern 5: Evasive tactics

Breeding ecology of the Little Tern 5: Evasive tactics

The various aspects of the breeding ecology of the Little Tern (Sterna albifrons) have already been posted earlier - 1, 2, 3 and 4. This, the fifth part, deals with the chicks' evasive tacticts in trying to stay undetected. From day two onwards, the chicks are actually mobile. However, they choose to stay on the nest mound for longer periods for feeding (above). Within hours they can move down the corners of the mound to the valleys or even hide among the vegetation (above). This is especially dangerous as photographers have earlier learnt to avoid the tops of mounds. Hence during hatching time, the valleys and vegetation need to be checked with much caution. When chicks spot predators, they usually disappear into the shadows whilst the adults call overhead and perform dive bombing. This allows the chicks time to move to cover and remain motionless. They are rather clumsy at times. As they grow larger, they will continue to use vegetation as cover (below). Parents get into dive bombing mode with shreaks and calls to drive predators like dogs and other birds away from the vicinity of the hiding chick (bottom left). The chick only opens its mouth for food and stay still. The rest of the adults wll sound the alarm for all the rest of the hiding chicks to remain motionless.
Once the threat is gone, the chick will slowly turn its head to locate the next hiding place. It will check two to three times to ensure that there is no more threat before making a quick dash for the next cover. When it senses that predators are approaching, it will remain stationary irregardless of whether it has reached a safe location or not (above). The aerial distractions are the main source of challenge that makes detection of the chicks hard.

Input and images by Dr Jonathan Cheah Weng Kwong.

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