THE BLACK NODDY ANOUS TENUIROSTRIS ON ASCENSION ISLAND. PART 2. BEHAVIOUR.

Abstract

SUMMARYAt a breeding colony on Ascension, many Black Noddies remained throughout the year. The main part of the paper describes their behaviour, with special reference to daily rhythm, sunning, absence of “panics”, nesting (with possible value of the birds' own guano for cement), fighting, and courtship (with details of ground and aerial displays), copulation (apparently rare) and the behaviour of parents and young.On Ascension the birds nest on small cliff‐ledges, elsewhere they also use trees, both kinds of sites being relatively inaccessible to ground predators, unlike the majority of terns, which nest on the ground. As with the Kittiwake, another cliff‐nesting species which has diverged from ground‐nesting stock, a number of the Black Noddy's peculiarities can be related directly or indirectly to its nesting site. Indeed the occurrence in just these two species of two features absent in their ground‐nesting relatives indicates that there are some cliff‐nesting adaptations which had previously been overlooked. The Black Noddy's adaptation in this respect can be summarised as follows: Cryptic adaptations lost. Cryptic plumage of nestling and juvenile. Dispersal of egg‐shells and droppings. Adaptations acquired, and their consequences. Shortage of nest‐sites, focussing territory on nest, with consequent increasing, though not exclusive, importance of Bridling as “song”. Allopreening between mates. More elaborate nest‐building, with gathering of material (if available), which is cemented together with guano; side‐stepping and depressing tail when shaping nest. Young intolerant of others; crouch if threatened instead of running; peck at feet of intruders, or beak‐hide to appease attacks, precocious development of adult (threat?) plumage.The Brown Noddy is the closest relative of the Black, and what little is known of its breeding biology suggests it is less specialised for nesting above the ground, and that its ability to nest on the ground as well as in bushes and trees allows it to breed in localities where the Black Noddy could not.