Pure Joy

For a quarter-century, I have been censusing the birds that nest and breed in a 40-acre woods in the Pennypack Preserve.  On eight mornings at the end of May and beginning of June, I have awoken at the crack of dawn, wolfed down a quick snack, power-walked 20 minutes to the tract, and then begun censusing.  For the next three hours and ten minutes, I have scanned the trees with my binoculars and pricked up my ears to catch the slightest hint of birdsong.

The forest is not the most dramatic or beautiful woods in the preserve.  Most of it was farmland until about 1920, but a new owner abandoned agriculture and allowed the woods to return.  The canopy is still young and not very diverse - mostly quick colonizing and rapidly growing tuliptrees and ashes (which, alas, are now under attack by the devastating emerald ash borer beetle, imported from China).  Nevertheless, it is the woodland I've come to know the best in the preserve.

And I've come to know its birds, too, especially the Ovenbirds.  Ovenbirds are aberrant warblers that look more like small thrushes.  They skulk around furtively in the duff and the low understory, defending their territory with their distinctive and increasingly strident tripartite teacher-TEACHER-TEACHER call.  The birds are much more often heard than seen, but since I spend so much time in the woods with them, I'm bound to observe one or two each spring.

The Ovenbirds and their offspring are remarkably faithful to territories.  I could probably outline the birds' territories each spring without even venturing into the woods - which is what distressed me when I learned that a part of the woods I've come to know so intimately was for sale.  I originally included this five-acre woods in my census area because it was owned by an individual who I thought would never sell it for development.  I was proved wrong in 2016, though, when the owner announced plans to sell the land for housing.  The land included the territory of an Ovenbird (or its offspring) that I had documented from my very first census in 1991.

I could clearly imagine an Ovenbird returning to its breeding grounds from the tropics, anticipating re-asserting its territory, only to find that its woodland had been leveled.

Fortunately, the landowner was willing to work with the Trust to try to protect the land permanently.  The landowner delayed a sale until the Trust could work with the state to secure open space funding.

When the landowner finally sold the land to the Trust on Tuesday afternoon, February 21, I practically leapt for joy knowing that one Ovenbird pair evermore would have a place to raise its brood.

Unabashed Anthropomorphizing

Hooded Warbler (Wilsonia citrina) (Audubon image)

I have begun my annual census of the birds breeding in the heart of the largest, oldest and densest forest in the Pennypack Preserve.  I always begin the census on or around May 20.  This date is a compromise.  For early-breeding resident species like Carolina Chickadees, Tufted Titmice, and the woodpeckers (i.e., Northern Flickers and the Red-bellied, Hairy, and Downy Woodpeckers), they've already fledged their young, which accompany their parents begging to be fed and learning how to take care of themselves.  On the other hand, later breeding migratory species like Wood Thrushes, Veerys and Scarlet Tanagers are still establishing their territories on May 20, making counts this early in the season unreliable.  In fact, most ornithologists caution that migrants in southeastern Pennsylvania should not be tallied until they've settled down into territories beginning in June.

Each year, there are always a few late and errant migrants in my earliest counts.  This year, for example, I heard a Black-throated Blue Warbler on my first foray into the woods on May 19.  Black-throated Blues breed in the Appalachian highlands, New England, and southeastern Canada - they won't stay the summer in our humid lowland woods.  Sure enough, the bird was nowhere to be heard two days later; it had moved on north.

However, on my first counting day, I also heard a Hooded Warbler singing in the forest.  This bird is a furtive wraith rarely observed but much more often heard.  Its call is distinctive and unmistakable: wheeta-wheeta-WHEET-see'o, repeated loudly and incessantly from the dense forest understory where the bird is lurking.  Unlike most other warblers that breed further north and at higher elevations, the Hooded Warbler does breed in southeastern Pennsylvania, though it is rare.  I have only documented breeding pairs in two other years during the 24 years I have been censusing birds in the forest.

This spring's Hooded Warbler stood its ground, singing for 30 minutes while I conducted the census where it had staked out its territory.

Then, when I returned to the woods two days later, the warbler was still present, but it had moved its singing perch over the crest of a ridge and about a half-kilometer deeper into the forest.

All of which got me thinking.  (I have plenty of time to ruminate when I'm conducting the census.)

This poor Hooded Warbler, undoubtedly a male singing its heart out seeking a female, probably is out of luck this year unless it moves somewhere else.  This forest in the preserve, while good habitat, is small and surrounded by suburbia.  If there are no female Hooded Warblers in the forest, the chances of this male finding a mate are nil.  It's not as if he could just fly a few hundred feet further along in the forest to another spot in hopes of luring a mate; if he were to fly a few hundred feet, he'd be in the middle of someone's back yard or in a business campus.

I couldn't help but feel sorry for this seemingly desperate bird - so clearly ready to find a mate, searching throughout the forest but unable to locate a female.  If he does find a female, he'll sing most of the summer defending his territory.  More likely, though, he'll go quiet.  If that happens, I'll never know if he flew elsewhere where his prospects might be better, or if he simply sat out the summer to try again next year, here in the preserve or in another woodland.

If he stays, I'll keep you posted.  For my census, the year is young; for a bird trying to find a mate, the clock is ticking.   

Submitted by
David Robertson, Executive Director

Fly Month

This morning, as I was conducting the sixth of the eight forest breeding bird census counts that I do each year in late spring and early summer in Papermill Woods, I noticed my first hoverflies of the year cruising a sunny patch of woodland understory.

Adult hoverflies are a bit intimidating because superficially they resemble wasps or bees.  While the larvae of most species are carnivorous, the adults are exclusively nectar feeders (hence the family's other common name: flowerfly [family Syrphidae]) so I have no reason to be anxious. 

As the forest birds settle into their territories, the forest quiets down quite a bit, providing me opportunities to observe other wildlife like the hoverflies.  This morning, there were four of the flies in the patch.  All were facing the same direction, and they all "hung" in the air, lined up side-by-side about eight inches apart, patrolling their own tiny patch of air space.  Occasionally, one would break ranks for a second, zooming away (usually backwards!) but returning almost instantly to take up exactly as it had left off.  Their world is unfathomable to me, but they are endlessly fascinating to watch.                                                                   

I refer to June as Fly Month. It's the month when mosquitoes make their first appearance and when deer flies are most maddeningly abundant.  Furthermore, I'm no fan of hot weather, so the addition of pestiferous flies to the mix only makes June all the more challenging.  Of course, the forest nesting birds will soon have plenty of new mouths to fill, so perhaps I shouldn't complain about the superabundant dipterans too much. 

 

Submitted by David Robertson

Executive Director

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.

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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