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Flying Squirrels in Pennsylvania: Why Are They Endangered?

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There are two species of flying squirrels in Pennsylvania: Northern flying squirrels and Southern flying squirrels. The greatest concern among conservationists in Pennsylvania is the decline of northern flying squirrels. 

Northern flying squirrels are listed as endangered. But what is happening in Pennsylvania to cause this species to decline? 

In this article, we take a closer look at flying squirrels in Pa, find out why northern squirrels are in trouble, and what people in the region can do to save them. 

Northern vs. Southern Flying Squirrels in PA

Northern flying squirrels are native to Pennsylvania. Southern flying squirrels are not, but they are taking over the region. The notable physical differences include size and the coloring of their undersides. 

Southern and northern flying squirrels look similar and are both nocturnal

They also both have an extra flap of skin that extends from the wrist to the ankle. This membrane allows them to glide from tree to tree by acting like an airfoil when stretched out as the squirrel leaps. 

But, as similar as they look, there are two notably different species. 

Northern vs. Southern Flying Squirrels in PA
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Northern vs. Southern Flying Squirrels: Physical Appearance

The difference to look for is that northern flying squirrels are bigger and have gray fur covering their bellies.[1] Southern flying squirrels are smaller and have creamy white fur covering their bellies.[2] 

Northern vs. Southern Flying Squirrels: Distribution  

Another key difference is that northern flying squirrels are native to Pennsylvania, while southern flying squirrels are not. 

Southern flying squirrels are native to the eastern half of the United States, but climate change has spurred them northwards.[3] 

In Pennsylvania, southern flying squirrels are thriving and northern flying squirrels are declining at an alarming rate. 

An extensive study from 2003-2007 found only 33 northern flying squirrels in Pennsylvania.[4] 

SpeciesSouthern Flying Squirrel Northern Flying Squirrel 
Scientific NameGlaucomys volans  Glaucomys sabrinus
Description Gray-brown fur with a creamy white underside and a flap of loose skin extending from the wrist to the ankle that helps them glide. Gray-brown fur with a gray underside and a flap of loose skin extending from the wrist to the ankle that helps them glide. 
Size8.35–11.22 inches10.83–13.46 inches
Average Weight 2.30 ounces4.66 ounces
HabitatTemperate to sub-temperate forests in the eastern half of the United States, southeastern Canada, Mexico, and Honduras. Mature conifer and deciduous forests across Canada, south to the mountains of North Carolina, and west to Utah in the United States. 
Diet Omnivores Omnivores 
Lifespan3–5 years in the wild 4 years in the wild 

Where Are Northern Flying Squirrels Found in PA?

Northern flying squirrels are only found in mature forests in the northern parts of Pennsylvania.

Northern flying squirrels inhabit mature spruce and conifer forests with plenty of wooden debris on the forest floor. 

In Pennsylvania, they were once found across the northern region. Today they are only found in the northeast.[5] 

Northern Flying Squirrels
Image Source

Why Are Northern Flying Squirrels Endangered? 

The population of Northern flying squirrels is under pressure because of the loss of forest habitat and a specific fungi that is part of the squirrels’ diet. They are unable to adapt to urbanized habitats. Southern flying squirrels also expose them to intestinal parasites that are lethal. 

There are three main factors that have caused the demise of northern flying squirrels:

  1. Loss of mature forest habitat.
  2. Loss of hemlock trees and specific fungi. 
  3. Intestinal parasites contracted from southern flying squirrels. 

1. Loss of Mature Forest Habitat

Loss of Mature Forest Habitat
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Northern flying squirrels thrive in mature conifer and mixed forests.

Urbanization and the declining health of hemlock forests due to invasive insects have had a negative impact on northern flying squirrels in Pennsylvania.[6] 

Unlike their more resilient cousins (the southern flying squirrel) northern flying squirrels are not adapting to urbanized environments.

2. Loss of Hemlock Trees and a Specific Fungi

Loss of Hemlock Trees and a Specific Fungi

Northern flying squirrels have a specific diet and eat a specific type of fungi that only grows on hemlock and spruce trees. 

This fungus is a critical component of the northern flying squirrels’ diet. 

An invasive insect known as “hemlock wooly adelgid” has been sucking the sap and killing hemlock trees. This has killed the fungi that northern flying squirrels feed on. 

It is believed that the warming climate allows this invasive insect to thrive. [5] 

3. Intestinal Parasites Contracted From Southern Flying Squirrels 

While northern flying squirrels are in decline, the more resilient southern flying squirrel populations are increasing.

In the diminished forests of PA, these two species are now coming into contact and it’s bad news for northern flying squirrels. 

Southern flying squirrels carry an intestinal parasite (Strongyloides robustus). They can to live with it, but northern flying squirrels are not as resilient. The parasite is lethal to northern flying squirrels.[6] 

How The Decline of Northern Flying Squirrels Affects the Forest Ecosystem

Northern flying squirrels play a vital role in maintaining the forest ecosystems. Without them, Pennsylvania’s conifer forests may not survive. 

Northern flying squirrels eat fungi that grow on conifer trees and spread the spores of the fungi in their droppings. This helps more fungi grow. The trees use the fungi to improve their absorption of nutrients and moisture. 

In other words, the squirrels help the trees and the trees help the squirrels.

Without northern squirrels, the already dwindling conifer forests will continue to die. And without the conifer trees to cool the mountain streams, the water temperature will rise and be inhospitable to trout.[6]

The northern flying squirrel is also a critical prey animal for the endangered spotted owl. Helping the northern flying squirrel thrive can help protect this endangered owl too.[7] 

How The Decline of Northern Flying Squirrels Affects the Forest Ecosystem

Conservation Efforts to Save Northern Flying Squirrels  

A team of biologists and foresters are working on forest regeneration projects. Since habitat loss is one of the greatest causes of the northern squirrel population decline, protecting, restoring, and increasing their preferred habitat is a way to help protect this rare squirrel. 

In 2001, Wilkes University and Penn State Altoona started monitoring more than

500 squirrel nest boxes. Researchers captured and fitted 33 northern flying squirrels with radio transmitters. 

They found northern and southern flyings squirrels foraging in the same habitat, sometimes even sharing nest boxes. 

This poses significant problems for northern flying squirrels as they can contract and die from an intestinal parasite (Strongyloides robustus) contracted from southern flying squirrels.

Based on the researcher, the state was able to list northern flying squirrels as an endangered species in 2007.[8] 

To try and save northern flying squirrels in Pennsylvania, a team of a dedicated team of  biologists and foresters is working on tree regeneration projects in forested areas. 

They started by identifying areas where northern flying squirrels were traditionally found. These are also areas with the potential to be affected by the invasive hemlock woolly adelgid. 

The team started the painstaking process of growing red spruce trees from seed and planting the young tree in these areas. Hopefully, this reforestation project will encourage northern flying squirrels to flourish. [9] 


There are two types of squirrels in PA, USA: Northern and Southern flying squirrels. The population of Pennsylvania’s Northern flying squirrels is on a decline, while the population of Southern squirrels is on an incline.

While some types of squirrels have adapted to life in suburbs and city parks, northern flying squirrels are not able to thrive outside of their native forest habits. 

The plight of the northern flying squirrel highlights the need to preserve forests and mature trees. 

Conservation efforts restore our hope for the species and mankind as dedicated biologists and foresters work tirelessly to save these rare squirrels.  

About Monique Warner

Monique is an avid dog lover who grew up with dogs, cats, and budgies as pets. She has worked as a pet sitter and dog walker. With her passion for dogs and pets alike, she writes articles with the intention of helping pet owners solve their biggest struggles.

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