Optimizing Nest Spacing Aids Survival

holes on the side of a cliff in front of a blue sky and tree

Biological Strategy

Eave swallow

AskNature Team

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Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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Populations of cliff swallows survive in areas with limited breeding sites thanks to their colonial nesting behavior.

Image: Lance and Erin /

Cliff swallow colony with birds peeking out of the entrances.

Image: jahool /

Cliff swallow colony in a quarry in Aromas, California.

“Also of importance in the evolution of colonial nesting are the spatial restrictions which narrowly specialized behavioral characteristics impose on a species. The specialization, whether inherent or traditional, which restricts nesting gulls and alcids to small islands so limits the number of usable breeding sites that procreation of the species depends on maximum utilization of the available space. A similar situation applies in the Cliff Swallow. The special environmental requirements for nesting in this bird include importantly a protected overhanging cliff, or cliff substitute, a source of mud of suitable quality for nest building, and an open foraging area. Sites containing all these essential features in close proximity were decidedly rare in North America before European settlement, and if each adequate site because of extensive territorial requirements could support only one pair of swallows, the dispersion would have been dangerously sparse for procreation and survival of the species. Any behavioral mutations which served to reduce the size of the defended territory around the nest and thus permit colonialism would, under such conditions, have survival value and be perpetuated.” (Emlen 1952:196)