A plague of Common Grackles (Quiscalus quiscula) in Chester Co., PA

After spending literally thousands of hours watching wildlife all over the globe, yesterday I had one of the most surreal experiences of all — definitely a “top 5” moment. The observation didn’t occur in a remote rainforest locale, nor did it involve some rare species that I will likely never encounter again. No, this time I was blown away (quite literally) by a practically ubiquitous species, the Common Grackle (Quiscalus quiscula), within 10 minutes of my childhood home in Chester County, PA. I was present as a “plague” of grackles descended upon one of my favorite deciduous forest patches, at Warwick County Park just outside of Pottstown, PA..

I was peacefully walking along the forest trail, pausing every now and then to watch the occasional White-eyed Vireo (Vireo griseus) or Carolina Wren (Thryothorus ludovicianus), when suddenly a massive migratory flock of grackles descended upon the forest. My best estimate of the flock size is ~100,000 birds. I’m not kidding. The sound was unbelievable, a cacophonous choir of harsh buzzes and squawks, seeming to come from all directions at once. Typical for this time of year, the grackles were in various stages of molt. The molting tails were most noticeable; the birds with missing central rectrices resembled Dicrurus drongos in flight, and other birds looked downright messy and unkept.

They filled just about every space in the forest; swarms of grackles covered the forest floor and rose in waves as I walked past. Berry-laden trees in the middle-canopy were drooping under their weight, with grackle upon grackle perched side by side on almost every branch. The high canopy was also flooded with grackles, and a steady blur of grackles could be seen just beyond the canopy. In the “negative” space between the trees, there was an incessant swirl of grackles undulating in beautiful patterns that at once seemed like chaotic madness and perfect symmetrical order.

The birds were gorging on just about everything that was available in the forest: vertebrate, invertebrate, vegetable, you name it. I watched a grackle dine on a freshly killed Wood Frog (Rana sylvatica), and others perched nearby with mantises (Order Mantodea) and moths (Order Lepidoptera). On the forest floor, they scoured the ground beneath the dense Rosa multiflora, pulling invasive earthworms from the ground (interestingly, the only item they seemed uninterested in eating) and tossing the leaf litter to and fro. The effect on the forest was similar to a swarm of army ants (Subfamily Ecitoninae) prowling across the rainforest floor; everything in their path was disturbed. I can only imagine the selective pressure that such massive flocks exert on the ecosystems of small forest fragments like this.

And with that….they were gone. No more than 20 minutes after their arrival, the flock left in its wake an eerie silence and a trail covered with wounded (but uneaten) earthworms. Mind blown.

Warwick County Park



Categories: Exploration, Natural History, Ornithology, PhiladelphiaTags: , ,

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