Environment – Nesting behaviour

Many animals build nests to protect their young from predators, for thermoregulation and to keep offspring close and secure. Bird nests, in particular, display a wide range of variability – not just between species, but within them, too. Bird nests are art, culture, environment and biology.

Welcome swallow nests are bowl shaped, made with up to 1000 pellets of mud that’s collected a beak-full at a time, laid row upon row, and held together with dried grass. Thrush nests are also cup-shaped, but made from woven grasses, small twigs and leaves, and lightly lined with mud. Magpies make bulky nests from twigs, roots and man-made materials including wire, and are lined with hair and wool.

Banded dotterel nests are a shallow scrape on a sea shore. They don’t offer much protection from the elements, from rogue tides, from predators or from unaware humans and their dogs, cats, vehicles or horses.

Grey warblers create hanging domed nests with a little porch, made from wool, sticks, feathers and moss. Fantail nests are wee cups, made from mosses, dried rotten wood fibres and grasses, hair, fern scales, all tightly woven with cobwebs, with a tendril-like tail hanging underneath, presumably for camouflage.

Kingfishers burrow holes in clay banks, while kākā nest in holes in decaying trees with woodchips on the floor. Kea nest in crevices or burrows among tree roots and kereru nests are a platform of a few sticks in trees.

Kiwi create nesting burrows up to two months before they lay their eggs and sometimes they use a pre-existing nest. It’s lined with a messy collection of grass, moss and soft leaves. Once the kiwi is safely inside, they often pull branches and leaves across the opening to close it off and keep the interior warm and dry. Morepork/ruru nest in tree cavities, in clumps of epiphytes or among rocks and roots.

Studies show birds with flexible and adaptable nest building behaviour are better at coping with climate and environmental changes. Birds using basic nests in pressured settings, like braided rivers and beaches, are particularly vulnerable, as are ground nesting birds generally. Birds nesting in trees are susceptible to introduced climbing predators like cats and stoats.

The special skills that each bird knows to make a nest best fit for its own needs is often simply explained by instinct, as if birds just know. Some say birds learn from their parents, despite not being present when nests are being built. Some birds build their nests from left to right, and some from right to left showing the importance of individual traits. Other studies show that nesting behaviour is generated by hormone release, mate social cues, material availability and learning from practice.

Nests occupied through generations overseas provide archaeological insights, containing cloth from ancient human cultures. Increasingly, nests contain synthetic materials like plastic and twine.
Nests are wonderful, and they answer an age old question, ‘What came first, the chicken or the egg.’ The answer? It was the nest.