This Curved-billed Thrasher hopped down into the interior of the cactus, apparently working on a nest. She seemed to be using her beak to place and move materials around. Later, I went past the cactus again to check on her progress. There was no sign of a nest! Was she practicing? Measuring?
Researchers in Edinburgh were the first to publish a report that indicated nest building is a learned behavior, not instinct. Their observations revealed that nests are better designed and more efficiently constructed by birds that had built previous nests. There were also variations in the actions that individual birds used that indicated their behaviors are not automatic.
As stated in Ecology and Evolution Journal, bird nests are multifunctional structures that require considerable cognitive ability. Most basically nests are containers for eggs and a space to raise young. But they are more!
Nests must minimize predation on the young. Site selection is the primary tool here, with the local abundance of predators having an influence. Ground nests may be the safest in areas with lots of raptors. Here in the Sonoran Desert, several species place their nests in thorny cacti to deter predators. The nesting area must also offer nearby sources of food and nesting material.
Nests are designed to reduce parasites. Fresh greenery woven into the nest cup and replaced daily has a biocidal affect on parasites. Feathers lining a nest can hold bacteria that produce antibiotic substances. Urban house sparrows and house finches have added cigarette butts to their nest cups. How did they know that the cellulose acetate in cigarettes repel parasites?
Every nest is a microclimate designed to protect the young from the elements. The outer nest material provides structural support for eggs and parents, but also thermoregulatory effects. The inner nest cup is all about providing a dry warm microclimate. Feathers keep nestlings warm, but birds use less of this insulation as the spring temperatures warm. Overhead shade is important, as is positioning in relation to prevailing wind.
In some cases nests attract mates. Since nest building burns energy, those that can build the largest nests, or the most nests, appear superior. Nests can serve as signals to potential mates and potential competitors….see how great I am!