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\u00a0Given that a bird\u2019s nest is something so commonplace, it is strange that we don\u2019t really understand how or why they are constructed. With recent research, however, we are beginning to understand what causes such variation, and how nests function.<\/p>\n
Always spotting bird nests? Here\u2019s how to identify bird and mammal nests <\/a>when out and about<\/strong><\/p>\n Birds build their nests in many different places. Terns and plovers, for instance, scrape a rudimentary hollow into the ground, relying on the markings of their eggs for camouflage. Kingfishers<\/a><\/strong> and sand martins excavate burrows<\/a><\/strong> in sandy banks, laying their eggs safely out of sight. Warblers weave grass and plant material into neat cups, deep in the vegetation.<\/p>\n <\/p><\/div> <\/section> Many nests are discretely hidden from predators; others are glaringly obvious. The vast platforms of sticks built by ospreys in the treetops, for instance, are hard to miss, particularly as they are re-used and added to over the years. Grebes build conspicuous floating nests in large ponds and gravel pits (their eggs are incubated half-submerged in the water, yet somehow still hatch), while house martins plaster their familiar, semi-circular cups under roofing eaves by the countless muddy mouthful.<\/p>\n Nest structure is as variable as location, and the finch family in particular illustrates just how diverse a domicile can be. The larger members, such as the hawfinch and bullfinch<\/a><\/strong>, rely on loose aggregations of sticks fashioned into an open cup lined with a few roots or lichen, while smaller goldfinches and chaffinches build neat cups of moss and lichen lined with hair and feathers<\/a><\/strong>. Linnets opt for a simpler structure, weaving grass cups lined with roots.<\/p>\n But even similar-sized birds use contrasting materials when building nests. Great tits<\/a><\/strong> build a moss base and line the cup with hair. If a nest is mainly moss and leaves, then a pied flycatcher is at home. Tree sparrow nests are almost all feathers, while the elusive nuthatch builds its nest almost entirely using flakes of bark.\u00a0<\/span><\/p>\n It is often possible to identify a bird species from a nest, yet construction is not a fixed behaviour. Birds are adaptable and build homes that vary considerably in size, shape and \u2013 in particular \u2013 composition. Some of this variability depends on what materials are on offer. Pied flycatchers across Britain rely on leaves and moss to build the bulk of their nests, but are not fussy foragers \u2013 they utilise whatever leaves are most common in their neck of the woods. Similarly, blue tits often line their nests with feathers, but will readily use wool if sheep are grazing nearby.<\/span><\/p>\n Irrespective of variation in form and content, all bird nests are designed for one thing: egg incubation \u2013 and, in many species, chick rearing. A nest enables an incubating bird to maintain the correct temperature and level of humidity for her developing eggs, as well as providing protection from the elements and predators.<\/p>\n If a blackbird is successful, their nest will comfortably hold four fully grown fledglings later this spring, each the same weight as an adult, and the dwelling may be used at least twice this year. Likewise, if she has a good year, a blue tit will raise her single brood of an eye-popping 10 youngsters.<\/p>\n So, why do birds vary so much in their nest-building behaviour? And why use such different materials? Does all this effort really keep the eggs and chicks warm, safe, and secure \u2013 and, if so, how?<\/p>\n Nest building and egg formation require lots of energy \u2013 both the blackbird and blue tit<\/a> <\/strong>have to carry more than twice their own bodyweight to build their nests. The clutch of 10 eggs laid by the blue tit weighs as much as she does. Thus, anything that can minimise heat loss from the nest will help the adult to conserve its energy stores. The incubating adults will remain in good condition and be able to successfully forage to feed their impending hatchlings.\u00a0<\/span><\/p>\n Nonetheless, a nest is not a simple egg-container. The walls can be complex in structure and comprise a surprising range of plant and animal-derived materials that vary according to the prevailing climate. In the north, where springs are colder, blackbird and tit nests are more effectively insulated than in the warmer south. Yet, despite this variation, research has shown that a range of small garden bird species build nests that provide, on average, similar levels of insulation.\u00a0<\/span><\/p>\n Insulation seems to relate to the proportion of moss and hair in the nest walls. Birds appear to have found a range of solutions to the heat-retention problem \u2013 with varying degrees of success. Research in my lab has shown that chaffinches<\/a><\/strong>, for example, line their nest cups with a bounty of feathers and hair. Despite being only 6\u201310cm thick (about a third of the wall thickness), this layer provides 90 per cent of the total insulation for the whole nest wall. By contrast, the same thickness of the grassy blanket lining a blackbird\u2019s nest only offers 40 per cent.\u00a0<\/span><\/p>\nWhere do birds build their nests?<\/span><\/h2>\n
Why do birds build nests?<\/span><\/h2>\n
What are nests made of?<\/h2>\n