Archive for March, 2016

Overwintering

Friday, March 18th, 2016

Mourning Cloak

Early this month when I was at Ball Mill Resurgence Conservation Area, I noticed that there were a few butterflies around. This one was cooperative enough to land on a branch in the sun and let me photograph it. I didn’t know what kind it was, but I was surprised to see how worn it looked. Clearly this butterfly didn’t just emerge from a pupa.

I looked through my butterfly books, but couldn’t find it; I later realized that was because they’re much yellower when freshly emerged, fading to more white later. I posted it to the Butterflies of the Eastern US Facebook group, and within about 10 seconds I had a response; “Mourning Cloak”. And someone added, “they overwinter as adults.”

I was intrigued. In fact, I was shocked.  I realize that insects have to get through the winter somehow; beetles have larvae — grubs — that burrow in the ground, maybe some survive as eggs, that sort of thing.*  But an adult butterfly? Surely it would freeze. Even here it gets down into the single digits Fahrenheit — over 10 degrees C below freezing. How can they do it?

Not content to just wonder, I hit the literature. First I read about “freezing-intolerant” and “freezing-tolerant” insects. These were the accepted categories for overwintering insects at least into the early 1990s.    What I got from work by W. Block and K.B. Storey was that the former use antifreeze compounds to lower the freezing point of their cell contents, and survive as long as the temp doesn’t get below their supercooling point (SCP). The latter use nucleation compounds in their extracellular hemolymph to allow it to freeze while keeping the intracellular material from freezing.

But it turns out that it’s more complex than that. More recent work, summarized in 1999 by Brent Sinclair, puts all of these on a continuum. Most insects use both antifreeze compounds and ice-nucleating compounds in some combination. They lower their freezing temperature, but then they may also be able to survive below the SCP when actually frozen.

The butterfly in the photo, the Mourning Cloak – Nymphalis antiopa, is a member of the family Nymphalidae. While most Lepidoptera overwinter as larvae or in some cases eggs, many Nymphalids overwinter as adults. They crawl under leaf litter or under loose bark and wait for spring.

The Mourning Cloak doesn’t freeze until -20 C, and it can survive temps down to -34 C — well below any recorded temp in this area. To me it’s pretty astounding. These guys sit there and freeze solid in a cold winter. Then when it warms up, they thaw out, crawl out of where they were hiding, and fly away.

So which of the butterflies you’re seeing sat out the winter as adults?  “Hibernal Diapause of North American Papilionoidea and Hesperioidea,”** a 1979 review by James Scott, includes a handy table  listing each species’ hibernal diapause stage as E, L, P, or A (egg, larva, pupa, adult), with references to back them up.  For me in Southeast Missouri, the take-home message of the table is that Red-Spotted Purples and most Fritillaries overwinter as larvae, Swallowtails overwinter as pupae, and Brushfoots mostly overwinter as adults.  So the adults that overwinter that I’m likely to see include the Mourning Cloak; genus Polygonia – the Comma and the Question Mark; and genus Vanessa – Painted Lady, American Lady, and Red Admiral.

Question Mark

Polygonia interrogationis, the Question Mark

Eastern Comma

Polygonia comma, Eastern Comma

Red Admiral

Vanessa atalanta
, Red Admiral

Butterfly on lantana

Vanessa cardui, Painted Lady

*The process of getting through a cold winter by slowing down body processes and waiting somewhere is loosely called “hibernation” in insects.  More properly, it’s referred to as “hibernal diapause”.  Some insects have a quiescent stage when it gets too hot as well, which is “estival diapause”.

**The Papilionoidea superfamily includes all the butterflies except the skippers, which are in the Hesperioidea.  So together those superfamilies constitute “butterflies”.

NOTE: One more local butterfly that overwinters as an adult is the Sleepy Orange, Eurema nicippe.

March 5, 2016: Saturday along the river

Sunday, March 6th, 2016

Magnolia Hollow Lake

The MDC had Magnolia Hollow Conservation Area on its list for management plan public input the other day, and I’d never heard of it before. When I found that it was only an hour’s drive from me, I decided to go check it out. When I got out at the first parking area at around 6:!5 yesterday, it was already pretty birdy — yellow-rumps in the trees, sparrows flitting around, etc.

I walked down to the fishing lake, which is quite a pretty spot (see above).

The yellow-rumps were thick there,

Yellow-rumped warbler

and I spotted a GBHE perched in a tree way in the distance.

Great Blue Heron

I spent some time just sitting on a rock listening to the YRWAs chipping in the trees, and eventually walked back up to the parking area. I drove on, getting out briefly at each parking area. As I was pulling out of the campground parking lot, I noticed a fat little bird in the grass on the shoulder. I stopped and cautiously opened the car door, but he didn’t seem to be worried about me; it was an American Woodcock, bobbing up and down in the full sunlight. He was backlit, so my photos are a little oddly exposed, but it’s the best chance I’ve ever had to get a pic of one.

Woodcock

At the next parking area, I got out and instantly saw a raptor departing into the woods. I ran up to see if I could tell where it had gone, and I could see something perched in the distance. In the binoculars it looked like a koala, but I was pretty sure that was wrong. Fortunately, the camera gave a better ID.

Barred Owl

From the last parking area, a paved path leads to a little deck with a view of Establishment Creek emptying into the Mississippi. Between them there’s a large fluddle. With a spotting scope, that’s a good spot to observe waterfowl. I found Canada Geese, mallards, green-winged teal, wood ducks, and gadwall there, and heard a kingfisher as well.

View at Magnolia Hollow

Next I decided to move downriver a bit (and inland) by visiting Ball Mill Resurgence and its new sister area, Blue Spring Branch Conservation Area. I’d never been to the latter, and I didn’t want Mark Haas to get all the “First Seens” in ebird for it. It’s kind of a weird layout. There’s a parking lot with a sign:

Blue Spring Branch

But the path to get into the area starts about 1/4 mile down the road. I bushwhacked down the hill from the parking area through tall grass and brush, but I wouldn’t recommend that approach. At the bottom of the hill (where I met up with the path) is Blue Spring Branch. It’s a fair-sized creek, but there’s a ford that wasn’t hard to cross with rubber boots.

Blue Spring Branch

I crossed the stream, following the path when it veered across an old fence line into a marshy field. There were some sparrows, and a deafening chorus of frogs. Adding to the soundscape, someone in a farmhouse a quarter-mile to the east started practicing the flute. From there I followed deer trails uphill to the far eastern edge of the Conservation Area. While there wasn’t that much happening on the ground, a mixed flock of geese (Snow, Greater White-Fronted, and a Ross’) came over. I made a loop and wound up back at the Branch, where I flushed 5 Wood Ducks. Added 13 species to the ebird list for the area: take that, Mark!

Of course I had to go to Ball Mill as long as I was in the neighborhood. Things were pretty quiet there, but I did get a nice pic of a bluebird.

Bluebird

One of these days I need to go there after a big rain and see the resurgence in action.

Working my way southward, I headed for Red Rock Landing Conservation Area. Last couple of times I tried to get there, high water made it impossible. The MDC says you can’t get in when the Chester gauge is over 20 feet; Saturday it was at 17 and there was no problem. It was also pretty quiet — what do you expect in mid-afternoon — but there were two killdeer and a Wilson’s Snipe (new ebird record for the area) on the wetland. I walked down to the river and came back up, and saw an armadillo approaching along a side trail. I crouched down so as not to be conspicuous and got out the camera.

Armadillo

At full zoom, I got some decent pictures, but he kept trotting toward me so fast I couldn’t keep him in focus. I was starting to worry that he’d just run right into me, and even as I backed off the zoom, I couldn’t get all of him in the frame.

Armadillo

He hopped over a log just 5 feet from me, and when I turned to watch him go by he finally realized I was there. He quickly scuttled into the flood debris. Those guys really have nothing going for them but the armor — sight and hearing were clearly not priorities for them as they evolved.

Afterward I walked a mile of the trail up onto the bluffs. It was totally dead for birds except some eagles out on a sand bar in the Mississippi. Nice view, though, but it won’t be much after the leaves come out.

View from Red Rock Landing trail

It was interesting looking at the eagles from up on the bluff; one immature took off and flew across the sand bar to perch in a tree, and I was puzzled by the coloring in his wings — brown on his back, shading pretty abruptly to black on the wing tips. I’d never seen that before, but a quick look in Sibley showed exactly that pattern. Then I realized that I’m not usually looking down at an eagle in flight.

After a mile or so on the trail, it was about 2:30 PM, and I was getting a bit tired — I think my total walking distance for the day was about 9 miles. I headed back and went home. Total species for the day, 49. Not bad when neither shorebird nor warbler migration has started.