The effect of patagial tags is evaluated for 3 265 Cattle Egrets banded and tagged as nestlings over seven seasons. Tagging did not affect fledging ability of nestlings, nor did tagging operations increase nestling mortality in the colony. Mortality of first year birds was comparable to that recorded in other studies, but adult mortality appeared to be greater. The presence of patagial tags on at least one member of a pair did not affect the mean number of young fledged. There was no difference in the mean number of young fledged from nests containing tagged chicks and those with no tagged chicks. Tag loss was recorded in only a few nestlings and for 21 per cent of returning first year birds. The loss of a tag did not affect the behaviour of the bird but did reduce the efficiency of field observations. However, tag loss was not considered to be a major reason for declines in the number of observations where observer effort was high. Patagial tagged egrets had the capacity to carry tags repeatedly on long distance migrations similar to that of untagged birds. By attaching patagial tags to nestlings, far more data on the biology, ecology and migration of Cattle Egrets has been obtained than would have been possible with unmarked, metal banded or colour banded birds. Such data could be of reduced value if the tags materially affect the behaviour of the individual or population. By examining both tagged and untagged portions of populations wherever possible we have demonstrated that patagial tags are an invaluable tool for research on egrets.

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