Songbirds steal nest materials in Hawai’i forests ^{CEFR B2}

High in Hawai’i’s native forests, scientists have documented songbirds taking twigs and moss from one another’s nests, a behaviour known as kleptoparasitism. The study, led by UC Riverside entomologist Erin Wilson Rankin and reported by UC Riverside, tracked and measured this theft in the wild for the first time. Over six months a trained team watched more than 200 canopy nests and recorded when and how thefts occurred; the results appear in The American Naturalist.

Observers monitored nests of several native species, including scarlet I’iwi, crimson Apapane and yellow-green Hawai’i Amakihi. The Apapane were both the most frequent thieves and the most common victims, a pattern the researchers attribute to the species’ abundance in the forest.

Most thefts occurred between nests at similar heights, which supports a "height overlap" hypothesis: birds may encounter and take materials from nearby nests while foraging. In most cases the targeted nests were already abandoned, but about 10% of thefts involved active nests that were being built or that held eggs or chicks. Roughly 5% of the observed nests failed after a theft; the study notes failures occurred when nest structure was damaged or when parents left after disturbance.

The researchers also point to possible costs for thieves: stolen material can carry parasites or disease, and some species defend nests aggressively, though Hawaiian birds in these forests were generally peaceful. None of the studied species are currently endangered, but many native birds are being pushed into higher elevations by mosquito-borne diseases introduced by humans. Conservationists worry that shrinking, crowded habitat may increase competition for nesting materials and sites. Wilson Rankin and UCR biologist David Rankin say that understanding when and where kleptoparasitism happens could help design conservation actions to support at-risk species.