Birds steal each other's nesting material

Spektrum der Wissenschaft

25.4.2026

Translation: machine translated

Why not help yourself to your neighbour's nest if they are already further along with their nest building? For endangered species in Hawaii, this theft increases the risk of extinction.

Hawaii's clothes birds are among the most endangered bird groups on earth: of the 40 or so species that once existed, half are already extinct and most of the rest are severely threatened. A behavioural pattern observed in the forests of the archipelago is increasing the concerns of ornithologists, as the birds regularly steal building materials from each other's nests, as Erin Wilson Rankin from the University of California in Riverside and her working group report. This regularly leads to the unsuccessful cancellation of broods - but with low population numbers, every loss is potentially devastating.

This behaviour, known as kleptoparasitism, had been reported anecdotally by observant naturalists in the past. But it was Rankin's team that first systematically investigated it. Over a period of six months, the researchers involved monitored more than 200 nests of the three species of clothes birds I'iwi (Vestiaria coccinea), Amakihi (Chlorodrepanis virens) and Apapane (Himatione sanguinea). The latter is still a relatively common and widespread species and the one that most frequently stole nesting material and installed it in its own nest. At the same time, Apapanes were also the most frequent victims of this theft - unsurprisingly given their relatively large numbers.

In total, almost 40 nests were plundered to a greater or lesser extent. All birds preferred to steal twigs and moss from the nests, which they usually found while foraging and which were already abandoned in 90 per cent of cases. However, one tenth of all thefts were from active nests that already contained eggs or chicks. And of these, at least two were subsequently abandoned because the nest was destroyed or the incubating pair was disturbed too much.

This may not sound like much, writes Rankin in a press release, but many species of clothed bird are already under severe ecological pressure from habitat destruction and introduced species and diseases. The narrowed distribution areas mean that there are fewer alternative habitats for the birds, especially as they also serve as refuges for species that used to live at lower altitudes on the Hawaiian Islands. As a result of global warming and the destruction of original forests, they have retreated to higher altitudes, where they compete with the species living there. The researchers suspect that this has increased the risk of kleptoparasitism. For highly endangered species such as the Kauai Akekeʻe (Loxops caeruleirostris), of which possibly less than 100 animals have survived in the wild, this could increase the likelihood of extinction - provided the behaviour is more widespread and also occurs on other islands in the archipelago.

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