Pennsylvania State Bird Guide: History, Status, and the Scarlet Tanager Debate

Your complete guide to Pennsylvania State Bird Guide: History, Status, and the Scarlet Tanager Debate, featuring expert perspectives.

Between 2001 and 2018, annual flush rates monitored by Pennsylvania hunters and agency staff plunged drastically. For decades, biologists attributed regional oscillations to regular 10-year predator-prey cycles. By 2014, lab necropsies conducted by the Pennsylvania Game Commission (PGC) revealed a far more lethal driver: West Nile virus (WNV), transmitted by Culex mosquitoes.

When infected, ruffed grouse suffer acute myocarditis, severe heart tissue necrosis, and neurological failure. Mortality rates among young grouse chicks exposed to the virus in controlled lab trials soared past 70%. Pennsylvania's warming summer temperatures expanded mosquito breeding seasons, allowing the insects to infiltrate valley bottoms and mid-elevation woodlands that historically remained too cold for high vector densities.

Compounding this epidemiological blow is an acute landscape deficit: the statewide loss of early successional forest habitat. Grouse are obligate users of young forest, stands characterized by dense saplings, thick aspen suckers, blackberry thickets, and scrub oak that emerge 5 to 20 years after a major disturbance. These tangled stands provide two vital services:

• Abundant seasonal food sources, including catkins, berries, and high-protein invertebrate blooms for newly hatched broods.
• Inpenetrable overhead cover that shields ground-nesting birds from northern goshawks, red-tailed hawks, and coyotes.

Throughout the mid-twentieth century, widespread timber harvesting, charcoal production, and agricultural clearing created a mosaic of regenerating brush. Today, Pennsylvania’s public and private forests have matured simultaneously into vast, closed-canopy oak-hickory stands. The dense brush is gone, replaced by open park-like forest floors where adult grouse and vulnerable chicks are easily spotted by predators and exposed to disease-carrying insects.