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Monarch Butterfly Update: May 5, 1998

Today's Report Includes:

We Need Your Help!
Is everybody looking for monarchs? Please REPORT the first you see!

This is a very slow migration season. Sightings this spring are down by almost half from last spring. With your help, we can document substantial differences between the 1997 & 1998 seasons. This information is important in helping to monitor the eastern monarch population.

BUT-- You may have to look longer and harder this spring, so please keep your eyes peeled.

Remember: We need your help!
We can't track the migration without you.

Latest Migration News and Data
Over the past week, monarchs have been reported from some surprising places!

"I couldn't believe my eyes today when I saw my first MONARCH pass by," wrote Brian Dalzell from New Bruswick's Bay of Fundy (44.73 N, -66.75 W). "I know this is an incredible sighting, but I am certain of what I saw. At
first I thought it was a Mourning Cloak, but then I caught the characteristic flight and that, combined with the large size, convinced me it was indeed a MONARCH. After having seen several hundred over the years, you get a feel for them." (

In addition, monarchs have now been spotted in Minnesota and Wisconsin. Although early, it does stand to reason that monarchs could have traveled this far: Reliable sightings arrived from Nebraska 2 weeks ago, and the vegetation in these northern states is almost 3 weeks ahead of normal.
Trees are fully leafed out and milkweed is already 6 inches tall!

Latest Migration Map
As of May 5, 1998

Discussion of Challenge Question #11
Where Have All the Monarchs Gone?

As this chart shows, sightings reported to Journey North are down by almost 50% this spring:

Sightings Reported
1997 vs. 1998












Click here for Comparative Map.)

Challenge Question #11 asked, "If the monarch population was at a peak last fall, and if the low numbers this spring indicate a smaller population than Spring, 1997, then when do you think this decline might have occurred--and why?

After Dr. Lincoln Brower's visit to the sanctuary in late March, he had these thoughts:

"I am not sure, but I think deforestation and desiccation are playing a major role in monarch mortality in Mexico. When Monica Missrie and I visited the Sierra Chincua Site on 28-30 March this past spring (1998), virtually all monarchs had left and the local people said that the tourist season was closed there on 21 March. On 31 March we noted some monarchs still streaming down through Angangueo, presumably from one of the Rosario colonies. In walking up the Arroyo Barranca Honda into the mouth of the caynon in which the monarchs overwintered, we noted very extensive logging in the spring staging area, i.e. in the area where monarchs congregate just before leaving the Chincua.

"It had been a very dry spring, and when we were there numerous forest fires were burning in Michoacan, including one on the north side of the Chincua, and another very large fire on the top of Chivati-Huacal, another of the sanctuary areas.

"In my 21 years of observations in the butterfly area, I have never seen it so dry or the plants so water stressed. As I stated in my Morelia lecture in November, 1997, evidence is building that the overwintering monarchs are leaving Mexico prematurely. I attribute this to human-caused forest degradation.

"Let's hope that the monarchs recover over this summer, remembering that the migratory populations appear to be resilient. The problem is that the camel's load of straw gets heavier each year......"

Professor Lincoln P. Brower
Research Professor of Biology
Sweet Briar College
Sweet Briar, VA

Dr. Chip Taylor of Monarch Watch shared his thoughts, carefully reviewing each step along the monarch's way--from the fall migration to their return this spring. As you'll discover, Challenge Question #11 raises more questions than answers!

These are the questions he asks himself:

  • Did last fall's large number of monarchs make it to Mexico?
  • Did they die shortly after their arrival?
  • Did this winter's extreme cold reduce their numbers?
  • What was the effect of the unusually dry El Nino weather pattern of 97-98?
  • Were the monarchs in poor condition at the over-wintering sites?
  • Was this spring's 600 mile trip north across Mexico unusually dry?

    Link to Dr. Taylor's Full Discussion

"Our ability to explain the dynamics of monarch populations is still very limited," said Taylor. "It has been a quiet spring--but a normal spring, unlike the spring of 1997," he added. "Although the numbers of spring monarchs appear to be lower this year, their arrival times at new locations are near the long term averages."

Discussion of Challenge Question # 12
Beware of Imposters

As we track the monarch butterfly migration each spring, we are always concerned about accurate identification. How can we be sure people are not reporting the first viceroy they see, for example?

"What's the best field mark to distinguish between a monarch and a viceroy?" asked Challenge Question # 12.

"A viceroy has a black line on it's wing. A monarch doesn't," said Sam from Rhode Island. For a look at the black vein he describes, compare the lower wing of a monarch and viceroy. See any Field Guide to North American Butterflies--or visit the
Butterfly Website:

Challenge Question # 12 also asked several questions about viceroy phenology. Knowing the timing of the viceroy's development could help us predict when we might see them:

Q. Where do viceroy butterflies spend the winter?
A. Unlike monarchs, viceroys do not migrate. They spend the winter rolled up in a leaf of their host plant (willow or poplar). The larvae look like bird droppings--so who would bother them?!

Q. At what stage of their life cycle do they overwinter--as an egg, larva or adult?
A. Viceroys overwinter as 1st or 2nd instar larvae.

Q. When are viceroys FIRST seen in the spring where you live?
A. The answer to this question obviously depends where you live! However, you won't see an adult viceroy until:
  • Willow/poplar leaves emerge and are available as food for the larvae.
  • The larvae develop through the remaining instars (approx. 5 days) and the chrysalis stage (at least 10 days).

In Ontario and Minnesota, for example, entomologists say adult viceroys don't usually appear until June. However, this year could be much earlier due to early leaf-out.

But adds Karen Oberhauser, "Viceroys are not nearly as common as monarchs." So perhaps we need not be too concerned about mistaken monarch identities.

The Next Monarch Butterfly Migration Update Will be Posted on May 12, 1998.

Copyright 1998 Journey North. All Rights Reserved.