[Field Notes] Grafton Ponds Walk

 Recently I had a chance to take a guided walk with Zach from the Virginia Department of Conservation and Recreation's Natural Heritage Program at Grafton Ponds Natural Area Preserve (NAP). I've talked about Grafton Ponds several times in the past, most recently this past spring when I did a bird walk with some friends.

The walk was in celebration of the 40th anniversary of the Natural Heritage Program and one of several they are doing around the state. Grafton Ponds is special because it has a large number of sinkhole depressions that collect water and then dry out annually. Sometimes called vernal pools or ephemeral ponds, this cycle of wet and dry throughout the year provides good places for amphibian to lay eggs. Fish are one of the main predators on tadpoles and eggs. Since the ponds dry out, the fish can't survive so there are fewer predators for the young amphibians to deal with. There are approximately 200 such ponds in Grafton Ponds complex with about 70 or so in the Natural Area Preserve proper. Depending on the water level, there may be three nearby ponds or a single, larger pond, making it hard to get a precise count. 

The ponds form when water collects and slowly seeps through bedrock that is dissolvable. Often that is limestone. Here on the coast, the bedrock is fossilized shells from a few million years ago, part of the Yorktown formation. Appropriate since the preserve is just outside Yorktown. The ponds continually form as the bedrock is removed and fill in as more sediment fills in the ponds. Zach told us that some of these ponds have been dated to 40,000 year ago while younger ones are around 350 years old. The older ones have a lot of spruce pollen in the sediment dating from the last ice age when spruce could live here. The younger ones formed around the end of a dry era that coincided with the arrival of European settlers. The settlers at Jamestown and other early colonies had trouble finding sufficient fresh water and that is attributed to salt-water intrusion to aquafers due to the extended dry period. As the rains returned, ponds started forming again. The Europeans also removed a lot of trees. The trees pulled up a lot of rain water. Fewer trees means more water to dissolve the shells and make sinkholes.

Some fossilized shells found along a stream bed

Life and Death in Grafton Ponds

Grafton Ponds Natural Area Preserve is a unique ecosystem here in coastal Virginia. The area has sinkhole vernal pools, ponds that fill up in the wet season and generally dry out in the summer. Vernal pools are critical habitats for a wide-range of amphibians who can lay eggs and grow up in this pools without having to survive hungry fish. Since the pools dry out every year or two, they can't support fish populations. The amphibians either leave the pools and live on land or bury down into the mud and leaf litter during the dry season.

One of the vernal pools that has already dried out

Through the Master Naturalists, several years ago I was part of a vernal pool mapping project and had the chance to go out and look for animals using the pools. This year we have started up a bird life survey of Grafton Ponds. My wife and I were joined by a couple of Master Naturalist friends to do a first survey. We were hoping there would be a good range of migrants coming in and using the area as a stop-over. Unfortunately, the weather hasn't been too conducive to migration around here for a while and the species count was below what I was expecting. We ended up with 25 species in the area. We also encountered several butterflies and dragonflies and a couple of snakes [WARNING: potentially disturbing photos, including snakes, below].

This spring has been quite dry, so several of the pools were already dried out. I hope the tadpoles had a chance to grow up before all the water left.

And a pool that still has some water

As we were approaching one of the pools, we started seeing some feathers on the ground. Soon there was an entire pile, and then another, bigger pile. And more scattered even further. 

After investigating them, we concluded these are turkey feathers and likely came from one unlucky individual. There wasn't much else left of the bird and were aren't sure who the predator was. Perhaps a coyote? Not sure any other bird would be able to take down an adult turkey and leave so little.

We also happened upon this black racer snake eating what looks to be a worm snake. My wife and I had never encountered a worm snake before but they came up in conversation early on the walk. Then our first encounter is one being preyed upon.

Swallowing prey

Gone

Yum

The day before our walk a big cold front passed through and dropped the temperature about 20 degrees (we were out on another bird walk then and everyone was putting on jackets during the walk). It was still chilly but the sun came out and we saw several animals enjoying the sun's warmth including several butterfly and dragonfly species.

Red-spotted purple (top left), eastern tiger swallowtail (top right), common whitetail (lower right), and common green darner (lower left)

Of course, this was meant to be a bird walk and we did encounter some birds. As mentioned, the birding was a little slow and we had to identify more birds by sound than sight. But there were a couple of birds that gave us good looks. 

First was this great egret that circled over one of the vernal pools. It made three or four passes and was catching really nice light.

Great egret

Great egret

Later we heard an ovenbird calling in the distance. They are just arriving in the area and I was the only one of the group to have seen one so far this spring. We tried tracking the bird but either the call was off in the distance or deep in some undergrowth. Even with extended searching, we couldn't find the bird. So we just moved on. A few minutes later my wife glanced around and saw a small bird sitting at eye level just off the path. The other three of us had walked right past it. A quick look confirmed it was an ovenbird. A second hopped up from the ground and then flew off but the first just stayed seated on the branch. And it posed for a long time letting me get a good range of photographs. Finally, we had our fill and let it be. Neither of these ovenbirds ever called; interesting!

Ovenbird

Ovenbird, notice the nice striping on the head

All in all, it was a good trip. Not as many birds seen as hoped for but more snakes and insects than expected. It has been several years since we have been back to Grafton Ponds and it was good getting reacquainted we the beautiful landscape. Looking forward to more survey trips out this over the next year or so and discovering other aspects of the Preserve.