This is a valid point and if we thought for a moment that compensation for the tag recoveries had a negative impact on the monarchs we would no longer offer it.
Here's an article Chip wrote for the most recent email update (July 23, 2004 edition
) that addresses this very issue:
10) Why Tagging Won’t Lead to the Demise of the Monarchs
Some of our correspondents have been concerned that offering a reward for recovered tags in Mexico would lead to activities by local residents that would result in damage to the monarch population. Actually, I was reluctant to initiate payment for tags for similar reasons and didn’t do so during the early years of the tagging program. However, the number of recovered tags was low as there was no incentive for the guides and local ejido members to look for and save tags. The number of recoveries jumped dramatically once we began offering compensation to those who saved tags for us. Over the years we have monitored the tag recovery program to be sure that no damage is done to the clustered butterflies. Most of the tags are found on dead butterflies along trails and under trees festooned with monarchs. A few people capture tagged butterflies as they take up water at seeps along small streams. In these cases, the tags are removed and the butterflies are released.
The rate of tag recovery is related to the mortality at the overwintering sites. In the winters of 2002 and 2004, years of massive mortality due to winter storms, the recovered tags numbered in the thousands. During years in which the mortality of the clustered butterflies is low, such as 2003, the number of recoveries was minimal being only 125. Clearly, the number of recoveries is related to the mortality experienced by the monarch population at the overwintering sites and not the activities of people who harvest the tags from clustered butterflies. The latter is virtually impossible because the ratio of untagged to tagged monarchs is quite high. Last winter we made our first attempt to define this ratio by counting the number of tagged monarchs among thousands of dead monarchs collected from one of the sites at Sierra Chincua where most of the monarchs had been killed by a winter storm. It took 4 of us much of our spare time over 4 days to examine 40,000 monarchs for tags and we found only one tagged butterfly and one from which the tag had fallen off. Given a ratio of 10,000-30,000 to one, it just isn’t feasible for the residents to knock down clusters of living butterflies, many of which would take flight, to recover a tag or two. We remain quite confident that the practice of paying for recovered tags is not contributing to the mortality of the overwintering monarchs.