Field experiments on the effect of ticks on breeding success and chick health of cattle egrets

Abstract Two experiments compared broods that were naturally tick-infested with an equal number that were rendered tick-free by application of an acaricide to their nests and of barriers against further infestation. In the first experiment conducted in 1991–92 nestlings in tick-infested broods had up to 159 larval ticks at once and a mean infestation of 23.6 larval ticks per chick per day. The chick's mean tick load was inversely correlated with its longevity. Chicks that survived to at least 18 days post-hatching had significantly lower larval tick loads than those that died by 18 days, excluding the third-hatched chick in each brood whose survival rate was low irrespective of tick-infestation. At 7 days post-hatching, tick-infested chicks had a lower haematocrit and higher polychromasia than tick-free chicks. I infer that blood loss anaemia caused the deaths of tick-infested chicks in their first week. None died in their second week and the demise of those in their third week may have been due to the paralysis manifested prior to their death. I conclude that heavy tick infestation of their chicks reduced the breeding success of the parent egrets below that of the egrets whose chicks were kept free of ticks. In the second experiment in the 1992–93 season the mean level of tick infestation was much lower (5.1 per chick) and these chicks survived equally with tick-free chicks through fledging.     

Seasonal movements of crayfish in a fluctuating wetland: implications for restoring wading bird populations

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