Waterbirds are known to disperse invertebrate propagules that survive gut passage, but there is very little information about
how the probability of dispersal changes at different times of the annual cycle when birds move in different directions, or
how it is affected by changes in diet. We studied internal transport 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 faeces 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 pellets,
and spotted redshank faeces were not sampled. Significant 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. Significantly fewer cysts were recorded
in redshank pellets in winter than in spring or autumn. Our results confirm that there is potential for long-distance dispersal
of
Artemia cysts via waders during both northwards (spring) and southwards (autumn) migrations.
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