Rocky Knob Migration Watch, Fall 2010: Report # 1

American Copper (

Lycaena phlaeas

), nectaring on white clover bloom.

Sunday 29 August 2010

Bruce Grimes & I arrived at Rocky Knob at Noon and stayed till 4 p.m. We were playing hooky from a lot of tasks that we both need to get done, but the hours of migration watch were worth it.

First, some background:

Rocky Knob Hawk Watch occurs at milepost 168 on the Blue Ridge Parkway. We watch from the Saddle Overlook sometimes, which gives us a fairly good view of Rock Castle Gorge to the east, and Buffalo Mountain westward. Mostly we watch from a large pasture just to the north of the Saddle Overlook parking lot. We affectionately call this location the Cow Pie Palace.

The hawk watch is occasional, mostly on weekends, and even then we seem to steal time from other activities. I wish that it could be closer to more daily monitoring of migration.

There are other hawk migration watch sites on the Parkway, and these are monitored far more frequently than our migration watch site at Rocky Knob:

Rockfish Gap (aka Afton Mountain)

Harvey's Knob

Mahogany Rock

If you are in this part of the universe, stop by and take a look for yourself: hawks are circling, gliding, soaring, flapping, hurrying or easing southward. So are many other species of birds: ruby-throated hummingbirds, chimney swifts, swallows, thrushes, warblers, tanagers, orioles, and many other kinds. And other creatures are pushing south also: several kinds of dragonflies, mostly common green darners, black saddlebags, wandering gliders, and twelve-spotted skimmers; and several species of butterflies too: besides monarchs, these include, Cloudless Sulphurs, Sleepy Orange Sulphurs, Little Yellows, Variegated Fritillaries, Eastern Commas, Mourning Cloaks, Painted Ladies, American Ladies, Red Admirals, and Common Buckeyes.

As soon as we got there yesterday, we noticed that Common Buckeyes, and Common Green Darners were flying by. We stayed busy trying to watch high and low for species that were on the move. The buckeyes mostly flew low just above grass blade and cow pie, but a few of them were actually fairly high up--one even buzzed a black saddlebags dragonfly, then flew on south. Some of the monarchs and buckeyes, the two most common insect migrants yesterday, would stop a while and refuel at thistle blossoms.

Tally for the 29th:

Raptors:

Osprey 1

American Kestrel 1

Other migrating birds:

Chimney Swift 16

Ruby-throated Hummingbird 5 (two were adult males)

Barn Swallow 5

Scarlet Tanager 2

Migrating butterflies:

Variegated Fritillary 1

American Lady 1

Painted Lady 1

unidentified

Vanessa

sp. 2

Common Buckeye 34

Monarch 31

Migrating Dragonflies:

Common Green Darner 20

Spot-winged Glider 2

Wandering Glider 1

Black Saddlebags 23

Carolina Saddlebags 1

Great Spangled Fritillary (Speyeria cybele), nectaring on thistle.

There were many other species of butterflies nectaring on thistles and other flowers in the fields: seemed to be gazillions of Pipevine and Eastern Tiger Swallowtails, one female Black Swallowtail, a few Spicebush Swallowtails, lots of Great Spangled Fritillaries (probably close to 100) and three Aphrodite Fritillaries, and one male Diana Fritillary. There were a few American Coppers, and a small horde of Peck's Skippers and Sachems!

The one Painted Lady that migrated through the field, stopped a couple of times for a portrait pose while it nectared on some flowers. Bruce got some pictures of this critter, plus some of the other butterfly species.

Hopefully there will be a few more migration reports during September. Please do stop by and check out the migration scene at Rocky Knob.

Painted Lady (Vanessa cardui), nectaring on a thistle flower. Thistles are also host plants for the caterpillars. Painted Ladies have nearly worldwide distribution, and are one of the most common migrating butterflies in the world.

A tale of 2 "nutty" butterflies- the buckeyes

Lemon Bay Preserve in southern Venice, FL, is an interesting place for many reasons, but it has some remarkable butterflies illustrating the role of habitat differences in speciation. For example during a nature walk there yesterday we saw a mangrove buckeye butterfly in a tidal area sitting on some saltwort (see photo). The name is a bit strange since the buckeye tree does not occur here; the tree is named for its large brown nuts which somewhat resemble the eye of a deer/buck. Indeed this butterfly does have 6 distinctive eye-spots, likely useful in deterring predatory birds. Buckeye butterflies often sit in open areas with their wings spread, allowing an observer to admire their unusual coloration. What really excites me about buckeyes at Lemon Bay Preserve is that there are actually two different but closely related species there, the mangrove and common buckeyes. The other photo shows a common buckeye that I found there on another day. If you look carefully you will notice some subtle but distinctive differences between these two sibling species.

The common has lighter or even white borders to the large eye-spot on the fore-wing; in addition the two eye-spots on its hind-wings are much more different in size than in the mangrove buckeye. While these differences are clear, they are not so striking that it is that easy to recognize them in the field.

So what is going on here? How can two closely related species co-exist in the same area without competing? The common buckeye is by far the most widespread in N. America (larvae feed on gerardia, toadflax & plantain) whereas the mangrove buckeye, as its name indicates, is primarily limited to the sub-tropical tidal coastline, and its caterpillar feeds mainly on black mangroves. This situation illustrates one mechanism by which new species originate- habitat specialization within one species splits off a separate species. Whereas speciation normally requires considerable geographic separation, the degree of isolation here is very small and due to juxtaposition of two distinctively different habitats (saline mangroves and adjacent uplands). Sometimes the argument is made that evolution is hard to observe, but here in our backyard we can actually see the end results among two "nutty" buckeye butterflies!

Bill Dunson

Englewood, FL & Galax, VA