To: Journey North
From: Dr. Lincoln Brower
Date: April 22, 1996
Here is our report on the 1996 spring migration into north Florida.
My student, Amy Knight, and I don't have all our data yet, but there appears to be a dismal monarch return this spring to our North Central Florida Asclepias humistrata site (The site is located near Cross Creek, along William Bartram's original natural history exploration route). The numbers are the lowest since we started monitoring the area in the early 1980's.
Last spring, by the third week in April, we had caught and released several dozen monarchs. This year we have captured less than a dozen to date. Instead of seeing up to 30 adults in an hour, we are seeing zero to three adults during each hour census. There was a small flush of eggs about 14 days ago and on 20 April we saw about a dozen fifth instars but no eggs and virtually no young larvae on the plants.
The reasons for the low numbers are indeterminate at this point. One hypothesis is that the extremely cool spring with several light frosts at the end of March has somehow affected the butterfly numbers. Another is that the December kill in Mexico was more general and severe than we thought it was. Yet another is based on a phone conversation with Bill Calvert in Austin, Texas who said that the rainfall there is far below normal. Perhaps the drought is affecting the wildflowers such that the butterflies are suffering for lack of nectar to replenish their critically low lipid stores.
If the conditions across the eastern US and southern Canada for the early and later summer broods are good this year, then perhaps the monarch can bounce back. If not, we could be in for a precipitously low fall migration.
Lincoln Brower and Amy Knight, University of Florida.