Nest site selection and cost of nest building by Cliff Swallows (Hirundo pyrrhonota)

Abstract

We studied the amount of energy and time required for the construction of nests by Cliff Swallows (Hirundo pyrrhonota) and examined whether swallows select sites that minimize their energy and time investment. Cliff Swallows build nests that may be detached (sharing no walls with neighbours at the time of initiation), semidetached (sharing one wall), or row nests (sharing two walls). Detached nests weigh 13.9% more than row nests (652.8 vs. 573.1 g, respectively), require 97.2 km more commuting (797.7 vs. 700.5 km), and cost 0.91 kJ/individual more during each day of construction (daily investment 7.49 vs. 6.58 kJ/individual). When building nests, swallows commuted from 50 to 320 m to mud sources and they increased their flight speeds as commuting distances increased. This limited the time required for nest construction while increasing the energy cost. Swallows showed a preference for sites where they could build attached nests and we argue that they act to minimize their time investment.