Function of the waterfowl nests as reproduction and living areas for leeches (Annelida: Hirudinea).

Some species of leeches migrate into waterfowl nests and use these both as general habitats and to deposit cocoons, but ecological associations between leeches and birds are not well understood. In the present study, characteristics of waterfowl nests both as living area for leeches (Hirudinea) and as reproduction areas for select hirudinid leeches (Hirudo verbana and Haemopis sanguisuga) was investigated in both natural and controlled laboratory conditions. A total of 48 leeches were detected in 23 of the 51 nests surveyed in natural habitats. The leeches were detected more frequently but there were less dense populations in the nests of the great crested grebe (Podiceps cristatus) (frequency: 57 %, population density: 0.71 ± 0.76 leeches/nest), and leeches were detected less frequently but there were more dense populations in the nests of coots (Fulica atra) (frequency: 36 %, population density: 0.91 ± 1.70 leeches/nest). Although the hirudinid leeches naturally reproduce between June and September, cocoons were only detected in August and September, when the nests were not actively used by the waterfowl and when water depths were less. In laboratory conditions, gravid medicinal leeches prefer moist peat rather than waterfowl nests for cocoon deposition. Results from the present study indicate leeches more frequently use the nests of coots, which have both dry and wet layers, compared to the nests of the great crested grebe, which have only a wet layer. Leeches were also found to be more prevalent in bird nests during spring months, during the reproductive periods of the waterfowl.

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