Water birds bring up the subject of plant dispersal

Posted on December 13, 2016

Waterfowl play an important role in the dispersal of plants by consuming and then defaecating their seeds. However, although birds such as ducks ingest a wide range of seeds, the digestive activity in their guts generally means that soft-bodied seeds become non-viable. Regurgitation of still-intact seeds is a possible alternative method of dispersal that allows the rapid colonisation of wetlands by plant species that are susceptible to the damaging effects of digestion. Dutch biologists fed eight mallards (Anas platyrhynchos) with high and low volumes of seeds from ten wetland plants (including sedge, water-lily and bugleweed), and monitored regurgitation and defecation of seeds over 24 hours. The high-volume trials mirrored the tendency of mallards to take advantage of sudden peaks in food availability by gorging themselves. Shortly (1-3 hours) after high-volume feeding, seeds of all plant species were regurgitated, seemingly in response to overfeeding. In contrast, after longer time intervals (10-12 hours), regurgitation was limited almost entirely to large seeds, which were probably those that hadn’t been broken down in the gizzard and were too big to enter the small intestine. Because regurgitation is impossible during flight, and therefore occurs after birds land, it acts as a more directed long-distance dispersal mechanism than “scatter-gun” defecation.

Reference: Kleyheega, E. & van Leeuwen, C.H.A. 2015. Regurgitation by waterfowl: An overlooked mechanism for long-distance dispersal of wetland plant seeds. Aquatic Botany 127, 1–5. http://www.caspervanleeuwen.info/images/PDFs/Kleyheeg_and_Van_Leeuwen_2015_Aqua_Bot.pdf