Straying or Stretching?

Long-tailed skipper missing its tails photo’d by Cynthia Allen in her garden on 9-3-12.

A second long-tailed skipper, with both tails, photo’d by Cynthia in her garden the very next day, 9-4-12. The northernmost area of the species’ regular breeding range seems to be in North Carolina or southern Virginia. Why do they and other “autumn vagrants” come our way?

Six butterflies are generally considered called “southern migrants” or “autumn vagrants” in our area because they wander up here in late summer/early fall with some regularity although their recognized breeding ranges do not reach New Jersey. None of their life stages — eggs, caterpillars, crysalids, or adults — seem able to withstand our winters, but each fall we see at least a few individuals of most of these species.

This year we have had all six species push up here earlier than expected. All first appeared before September 1st, four of them weeks or months before:

little yellow FOY on May 6
cloudless sulphur FOY on May 26
fiery skipper FOY on June 30
Ocola skipper FOY on August 9
sleepy orange FOY on August 23
long-tailed skipper FOY on August 29

Each of those dates is the earliest we have recorded for the species in our five years of logging, except August 23 for sleepy orange, our second-earliest FOY.

The most apparent explanation for these “wrong-way” flights is that they are a way for the species to stretch the limits of its range. Sending doomed pioneers northward each fall could work for the species if the climate eventually changed and enabled some to survive.

But that explanation has a flaw. A species is not a community working together. Instead, each is a set of individuals all working for themselves to preserve their own genes in future generations.

If the individuals crossing Delaware Bay and moving northward cannot leave successful eggs, caterpillars, and chrysalids that become adults surviving to breed themselves, what do vagrants gain by their long flights? They seem like sacrificial victims to a widespread urge that may be good for the species in the long run but seems entirely wasteful for wanderers individually.

A good-for-the-individual explanation would work if there is a return flight by the off-spring of these late summer wanderers, but have we ever seen any evidence for that?

Another, related question:

Is this year’s pattern — all six species here and earlier than usual — simply a flukey event, or is it a sign of things to come in future years? Over the next two or three decades will cloudless sulphur and perhaps one or two of the others follow the sachem’s apparent path over the past several decades and push their breeding range into our area?

Ocola skipper at CMBO’s Goshen garden photo’d by Chris Tonkinson on 9-4-12.

Ocola in Port Republic 9-1-12.

Little yellow photo’d by Sam Galick near his driveway 9-8-12. Sam notes: “It was ovipositing eggs on partridge pea in an area where I decided not to mow the grass yesterday because I saw partridge pea — in the off chance that a little yellow would stop by, and what do you know? Sweet!”

For more on this puzzle of “wrong-way” migration, see: Pied-Piper Migration

For a discussion of the connection between global climate change effect and the expansion of a number of southern butterflies into Massachusetts, see Another Reason Good Reason To Do What We Do

Keep exploring, everyone. Can we find a seventh autumn stray — now that the official start of autumn is actually close?


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