Monday, 16 June 2014

Precocial and Altricial young

Birds in Scotland are busy hatching and rearing their young at the moment, with June being the month when most species have dependent young at some age. I have been ringing, with other members of the Grampian Ringing Group, various species of chicks from common and tiny Willow Warblers to large and rare Golden Eagles, and all sorts between. While doing so, I have as ever been impressed by how well each species has adapted the best method of post-egg development to suit its lifestyle.
Common Gull eggs, with cracklines and holes - the chicks are beginning to hatch

I have been ringing gull and wader chicks and took a sequence of photographs at one Common Gull colony to show the development of their chicks. The typical clutch size is three eggs and the chicks hatch one after another, over about two days. The first chick to hatch stays in the next and are brooded by the adult birds until the last chick hatches and dries. Then they all begin to wander from the nest, usually set on the ground, and hide beneath the surrounding vegetation.

One dry chick, one wet chick and one still on its way out

Gull chicks have cryptically-coloured down which keeps them concealed from predators and warm. They can walk sand run strongly and are known as precocial young.

A fully dry Common Gull chick - two days old and now three metres from the nest

Or rather, gull chicks are better described as Semi-Precocial young, those which are downy and can walk and can leave the nest soon after hatching. e.g. in the case of terns and gulls, although they still rely on their parents for heat and nourishment.

True fully precocial, self-dependent young would be such as Mallee Fowl which find their own food without even guidance from either parent.

This is so different from the familiar nestling birds, which are Altricial - where the young are naked, blind, weak-limbed at hatch and rely totally on their parents for food and heat.

Semi-altricial young such as raptors are downy at hatch, but weak and rely on their parents for heat and food.

Four Skylark chicks in their nest

Two other terms which are used to describe young birds are; Nidifugous - those that leave the nest soon after hatching, generally once the whole brood has hatched and their down dried, and Nidicolous - those which remain in the nest for several days or weeks after hatching.

A three-day old Skylark chick, still partially naked and blind

The nestling stage is a very vulnerable period for young birds and the variety of concealment and protection methods taken by the parent birds is, to me even more fascinating. From secretive single nests to noisy colonies, each works for the protection of different species. But more on that later.

Five kestrel chicks - ranging from about one to two weeks old

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