Nest-building birds help disperse cotton

Cotton fibres have long been seen as an adaptation for wind dispersal. However, research in southern Africa, in Mbuluzi Game Reserve in Eswatini, shows that birds can be at least as important. In this savannah area, researchers studied wild cotton (Gossypium herbaceum) and the nest-building behaviour of two species of mousebirds. The plants were naturally occurring, not part of commercial cotton fields.

Not wind, but birds

The research focused on two species of mousebirds in Eswatini. These birds use the soft cotton fibres as nest lining. In several nests that were examined, large numbers of cotton seeds were found – sometimes more than two hundred per nest. The seeds remained intact in the fibres. Using colour markings, researchers were able to trace where the seeds had come from. Some had been moved more than a kilometre from the parent plant.

Notably, mousebirds normally remain within a few hundred metres of their nest during the breeding season. To collect cotton, they therefore travelled greater distances than expected. When nests fall apart after the breeding season – often during the rainy season – the seeds end up on the ground under favourable conditions for germination.

Actively collected nesting material

Cameras at the nests showed that the birds deliberately collected the cotton and carried it to the nest in their beaks. The material was incorporated into the nest structure and was even reused from old nests. Because of this reuse, seeds may possibly be dispersed even further in multiple steps.

Sjouke Anne Kingma, researcher at Wageningen University & Research: “We saw that the birds actively searched for cotton and brought it to their nest. That means that their behaviour contributes to the dispersal of this plant. Cotton is such a familiar material for people, and it is remarkable that its natural function – and thus why cotton fibres evolved – has remained hidden for so long.”

Implications for biodiversity

This study shows that nest building is not only important for the birds themselves, but also for the dispersal of plants. Seed dispersal determines where plants establish and how populations remain connected. Sjouke Anne Kingma emphasises the broader significance: “Animals are not only inhabitants of ecosystems, but they also shape them. By building their nests with plant material, they influence where plants establish and how biodiversity develops.”

In a time of climate change and habitat loss, this insight is important. If animals disperse seeds over greater distances and also carry them across barriers such as rivers or fragmented landscapes, plants can reach new areas. This contributes to the resilience of ecosystems. The loss of animal species may therefore also have consequences for plant communities.

More information

• Article: Cotton facilitates long-distance seed dispersal by functioning as nest material for birds.

Text: Cecile Leuverink and Sjouke Anne Kingma, Wageningen University & Research
Images: Wageningen University & Research (lead image: mousebirds nest in Mbuluzi Game Reserve, Eswatini)