Overlooked costs of coloniality: Mislaid eggs and the double Incubation of separate nests

The evolution of colonial breeding remains an outstanding question in
evolutionary biology, in part due to our limited understanding of the
costs and benefits of group living. We document 85 cases of Barn Swallows
Hirundo rustica erythrogaster laying, and subsequently abandoning, eggs in
empty, unclaimed nests located adjacent to active nests during a six-year
study. The frequency of this behavior was positively correlated with total
available nests, a metric that increases with colony size. In addition,
two female swallows were observed alternately incubating multiple clutches
after mislaying eggs in neighboring nests. We argue that the potential to
mislay eggs and allocate parental care across separate nests may represent
an overlooked cost of colonial nesting in birds.