Thursday, June 20, 2013

Redbird Smackdown

Northern Cardinal (Cardinalis cardinalis) [image from Internet source]
For the last 22 springs, I have been censusing the birds nesting in a 40-acre forested section of my preserve.  The censuses involve walking a rough path through the forest, stopping every 50 meters and then observing and listening quietly for 10 minutes to try to delineate breeding territories.  I have to do this eight times over the course of the late spring (Cornell Laboratory of Ornithology protocol), and each individual census takes 3 hours and 10 minutes to complete, plus 15 minutes walking to the forest and 15 minutes back.  I'm really glad when the last of the eight censuses is completed each year, since I have to awaken at 5 a.m. to get to the forest by sunup.

With two decades of observations under my belt, I've noticed a few trends, but nothing earth shattering or spectacular.  For example, Red-eyed Vireos (Vireo olivaceous), one of the most common birds early in this series of surveys, have nearly disappeared, an observation that I attribute to the fact that the forest has gotten more mature and Red-eyed Vireos are birds of woodlands and young forests.  I've also stopped observing Brown-headed Cowbirds (Molothrus ater)--a great thing, because cowbirds are nest parasites that lay their eggs in other birds' nests and allow the "other" birds to foster the aggressive cowbird chicks, usually at the expense of their own young.

This year, however, I noticed a real shift in the "redbirds," the Northern Cardinals and the Scarlet Tanagers.  Cardinals are usually among the most common birds in the forest; 6-8 territories in the 40 acres is not uncommon.  But this year, I only had two cardinal territories; I wonder what's up? 

In contrast, I had three pairs of Scarlet Tanagers nesting in my forest, an area where I'm usually lucky to get one pair.  It was really a treat to be greeted by their gravelly call from high in the treetops, and to be able to watch the males defend their territories.  The Cornell Lab has estimated that 10% of all Scarlet Tanagers worldwide nest in Pennsylvania, so I'm glad that my preserve can provide them with some of the habitat they so desperately need.  I hope that they're back again next year in even greater numbers. 

Scarlet Tanager (Piranga olivacea) [image from Internet source]
By the way, last winter, taxonomists (the scientists who classify living things) saw fit to group together cardinals and tanagers into a single genetically related group, the tanager family Thraupidae.  I sure hope they know what they're doing, because to my eye, these birds could hardly be more disparate.
Wood Thrush (Hyloxcichia mustelina) [image from Internet source]
On the eighth census this year, completed on Sunday morning, June 16, "action" was limited at some of the listening points.  (As the breeding season progresses, the woods tend to become increasingly quiet; birds have established their territories and it only takes an occasional foray to the edge of the territory to fend off one's neighbor, so the birds can concentrate more on raising their broods.)  I always carry a pair of plant clippers with me to trim away the vegetation that constantly threatens to overwhelm the path, and I occasionally venture off the path to clip an errant Japanese honeysuckle vine that his twined up into an understory shrub or cut back an aggressive multiflora rose.

On this, my eighth census morning, I spotted a particularly large clump of flowering Japanese honeysuckle off the trail and so went over to clip the stem and unwind the vine from the spicebush plant.  No sooner had I clipped the vine than I realized I'd made a horrible mistake--a pair of wood thrushes had secreted their nest under the sheltering umbrella of the honeysuckle.  The birds flew off to the nearby bushes and scolded me harshly.

Once the honeysuckle dies, the leaves dry up, turn brown, and the whole umbrella-like protection disappears.  I probably ruined this pair of birds' breeding for the season with one well-intentioned but misguided clip of an invasive plant.  I'm still fretting over it. 
Submitted by
David Robertson, Executive Director

Tuesday, June 18, 2013

Belated Casualty

In the wake of Hurricane Sandy last year, I noticed that a "crack" had developed in the soil between a huge, old tuliptree (Liriodenron tulipifera) and the edge of the Creek Road Trail in the Pennypack Preserve.  The storm had undoubtedly tilted the tree up a bit, but not enough to tip it over.  (The trail adjacent to which the tree was growing had been a public road until 1984 when the Pennypack Trust petitioned the municipalities in the area to close and abandon several roads so that the right-of-ways could be incorporated into the trail network in the growing preserve.  About three miles of roads were eventually abandoned.  But I digress.)

The soil "crack," a few inches wide and about two feet long, appeared to be stable.  My wife and I walk the trail frequently and hadn't noticed any changes during the months following the storm.  Then, last week, our area received three periods of very heavy rain.  After the first deluge, one of our members telephoned on his cell phone to say, "I'm on the Creek Road Trail, and a huge tree has fallen away from the trail."  When the call came in, I knew which tree had fallen over.

Last evening, about a week after the tree toppled, Mary and I walked the trail to inspect the damage and take some photographs. Fortunately, as the caller had said, the tree had fallen away from the trail, but the root ball had torn up half the trail surface.  In the interval between the tree's falling and our walk, Pennypack's stewardship staff had built a wooden retaining wall and re-filled the trail surface with crushed stone.

As everywhere else we lost trees to Hurricane Sandy, we'll now have to do battle with the sun-loving invasive plants that will quickly colonize this gap in the forest canopy.  Tuliptrees are not valuable for lumber, so we'll just let the tree decompose over time in place.  And, as the limbs and branches decompose, we'll plant new trees to replace this impressively regal giant.
Submitted by
David Robertson, Executive Director

Tuesday, June 11, 2013

Licking His Chops/Snake Sex

Last week, Mary and I took a walk in the Pennypack Preserve after dinner.  As we rounded the corner in the Management Trail, we startled a white-tailed deer buck in velvet that had been eating.  I managed to get the camera "up" just in time to catch him licking his chops; it must have been some succulent vegetation.  This buck allowed us to watch him for a full half-minute before he finally spooked and ran off up the hill.

Then, last Sunday, in preparation for a walk, we connected with two friends who had bought a house adjacent to the preserve along the creek.  The previous owner of the house loved and protected all wildlife in her yard, including some pretty fearsome but non-venomous northern water snakes (Nerodia sipedon sipedon) that liked to curl up and sun themselves on the rocks lining her walkway.  I asked our walking companions (the new owners) if the snakes were still there, and they led me to the top of the steep streambank above the creek and encouraged me to look over the edge.

There, on a flat rock at the water's edge, were two of the snakes.
Northern Water Snakes along the creek; look on the light gray rock center right bottom
Serpents close up
When we returned from our walk an hour later, the snakes had moved to another rock.  This time, we caught them in flagrante delicto:
And, there was a third snake coiled up and sunning itself on the stones lining the walkway to the house!  Just like old times!

Submitted by:
David Robertson, Executive Director