Transport of brine shrimps via the digestive system of migratory waders: dispersal probabilities depend on diet and season

Waterbirds are known to disperse inverte- brate propagules that survive gut passage, but there is very little information about how the probability of dis- persal changes at diVerent times of the annual cycle when birds move in diVerent directions, or how it is aVected by changes in diet. We studied internal trans- port of brine shrimp Artemia cysts by migratory waders in the Odiel saltworks in south-west Spain. Viable cysts of parthenogenetic Artemia were abundant in the fae- ces and regurgitated pellets of redshank Tringa totanus, pellets of spotted redshank T. erythropus, and faeces of black-tailed godwit Limosa limosa during spring and/ or autumn migrations in 2001–2002, but were not recorded during winter. Godwits did not produce pel lets, and spotted redshank faeces were not sampled. SigniWcant correlations between the number of cysts in a pellet or faecal sample and the proportion of that sample constituted by Artemia adults suggested that most cysts were ingested while in the ovisacs of gravid females. The proportion of cysts destroyed during digestion increased when accompanied by harder food items or grit, and when fewer cysts were ingested. The median number of intact cysts was higher in redshank faeces than in their pellets, but cysts extracted from pellets were more likely to hatch. A higher proportion of redshank pellets contained Artemia cysts in spring than in autumn, but more redshank migrated through the area in autumn. SigniWcantly fewer cysts were recorded in redshank pellets in winter than in spring or autumn. Our results conWrm that there is potential for long-distance dispersal of Artemia cysts via waders during both northwards (spring) and southwards (autumn)migrations.

Peer reviewed