Handling Effects in Heliconius: Where Do All the Butterflies Go?

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Abstract
(1) ''Handling effects'' (abnormally high disappearance rates of net-captured individuals) exist in several species of butterfly, but it is not known whether this increased disappearance is due to dispersal, mortality, or avoidance of capture. In this paper we report work with Heliconius butterflies to differentiate between these alternatives. (2) We experimentally investigated handling effects of marked Heliconius individuals at flowers of the vine Psiguria warscewiczii. Individuals were less likely to return to flowers after being captured and handled than after being identified by sight alone. This handling effect lasted up to 2 days after capture. (3) On the other hand, fidelity to particular nocturnal roost sites was not affected by initial capture and marking or recapture during the day, apart from a short-term effect on the night of the day that captures were made. Heliconius avoid specific sites where they have been handled, but do not completely desert their home ranges; handling effects are not due to increased dispersal or mortality. This is the first time that such an effect has been shown in insects. (4) Because of these handling effects, mark-recapture estimates of population size are likely to be inaccurate. For butterflies like Heliconius, it may be necessary to catch almost all the individuals in an area to obtain a good estimate of population size, whereupon the Lincoln Index becomes unnecessary. Judging by the high rates of recapture, many studies may achieve this. (5) The natural equivalent of handling effects could enable Heliconius to avoid areas with poor resources, or sites where predators are likely to attack.