Category Archives: Deer

How Deer Create a Browse Line

Browse line in Schenley Park — gap below the trees — at the entrance to the Upper Trail, 18 August 2023 (photo by Kate St. John)

23 August 2023

The white-tailed deer population in the City of Pittsburgh has been so high for so long that most people think the browse line in our parks is normal, but the light-gap you see under the trees above is not normal in a balanced forest. It’s a sign of deer overpopulation. Here’s what a browse line is and how deer maintain it.

Browse line: A phenomenon that occurs when herbivores consume all of the vegetation in the woods between the ground and the level of their highest reach. A clearly visible line is formed between the leafed and the leafless areas.

paraphrased from Blue Jay Barrens: Fallen Trees and Browse lines, May 2011

Is the browse line hard to recognize in the photo above? Here’s an extreme example.

Tuileries Garden in Paris, a man-made browse line (photo from Wikimedia Commons)

This eye-level view of the Grande Allée of horse chestnut trees at the Tuileries in Paris is a man-made browse line in which gardeners trim the trees and clear the ground to maintain an opening beneath the trees at uniform height. Nothing is growing between the ground and the trimmed height.

An individual deer browsing the ground and lower branches of trees does not create the browse line. It’s the cumulative effect of too many deer eating at the same location over and over.

Last Friday I watched two 8-point bucks, antlers in velvet, maintain the browse line next to the Upper Trail at Schenley Park. The current browse line, seen in the video, is that clear view straight through the woods to the cars passing on the road beyond.

In the video the bucks eat herbaceous stems and leaves on the ground, then switch to twigs, leaves and stems of trees. About halfway in, the buck on the right stands on his hind legs to reach the lowest branches. The buck on the left wrestles with a tree to yank off the branches. Deer only have lower teeth so they can’t sharply bite off a branch like a beaver would.

Two bucks reinforce the browse line in Schenley Park, 18 Aug 2023 (video by Kate St. John)

In late August, when forage should be quite plentiful, these bucks are forced to eat their own cover and what little remains of the edible plants.

Buck in velvet has no cover to hide him, Schenley Park, Aug 2022 (photo by Kate St. John)

p.s. Here’s what the forest would look like if there was no browse line.

No browse line here, August 2023 (photo by Kate St. John)

(photos by Kate St. John)

The Calm Before The Rut: Deer in August

6-point buck in Schenley Park, 4 August 2023 (photo by Kate St. John)

13 August 2023

In the city of Pittsburgh there are so many white-tailed deer that it’s easy to see them in August. The bucks are eating, eating, eating to bulk up. The does are hanging out with their adolescent fawns in this brief period between birthing and mating. It’s the calm before the rut.

Last Friday morning I found eight deer resting in dappled shade in Schenley Park. My cellphone photos don’t do them justice except for this: The photos show how hard it is to notice deer that are lying down and not moving.

Four bucks resting in Schenley Park, 11 August 2023 (photo by Kate St. John)

A few of them moved, however, grooming to shed their chestnut brown summer coats for gray-brown winter pelage. The photo above shows four bucks with antlers in velvet, each with a different point count: 4-point, 6-point, 7-point and 8-point.

Two does and two fawns rested a short distance from the males. The fawns gave the group away. They did not hold still for long. (The second doe is not in the photo.)

Doe and two fawns resting in Schenley Park, 11 Aug 2023 (photo by Kate St. John)

One week earlier it was impossible not to see this six-point buck browsing the hillside right next to the Lower Trail.

Deer eating in Schenley Park, 4 August 2023 (photo by Kate St. John)

He’s leaving a lot of greenery behind but the leaves he’s not eating are unpalatable invasive aliens called goutweed. The buck is nosing through them to re-browse the deer-food plants hidden below the goutweed. Those food plants won’t recover this late in the season. All the food will be gone and he won’t be back to this spot.

Buck browsing in Schenley Park, 4 August 2023 (photo by Kate St. John)

In August the days are still longer than the nights and deer hormones are not surging yet but it’s only a matter of time and the Equinox before their sedate demeanor ends. According to the PA Game Commission, after 12 weeks of rut excitement from mid October through early January:

  • 98% of the mature does will have bred
  • 40% of the fawns will have bred at only 6-7 months old (city/suburb phenomenon)
  • 85% of the pregnancies will result in twins or triplets, some with different fathers.

It’s calm now before the storm.

Schenley Park suffers from its overabundant deer population. See this article for more information: The Forest Lives in Mortal Fear of Its Deer.

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(photos by Kate St. John)

Seen This Week

Prothontary warbler in Frick Park, 25 May 2023 (photo by Charity Kheshgi)

27 May 2023

This week’s big news was the unexpected prothonotary warbler that Charity Kheshgi and I found in Frick Park on 25 May. He was still present yesterday but BirdCast showed birds migrating out of our area last night so we’ll see if he’s still there this morning.

Migration is nearly over and the dominant landscape color in Pittsburgh now is green. It’s hard to remember that only five weeks ago (23 April) most of the trees were brown.

Daisies are blooming along meadows and roadsides, invasive wineberry is in bud, and bladdernuts have already formed green seed pods in the city parks.

Daisy blooming at Schenley Park, 22 May 2023 (photo by Kate St. John)
Wineberry leaves and buds, Schenley Park, 22 May 2023 (photo by Kate St. John)
Bladdernut seed pods, Frick Park, 23 May 2023 (photo by Kate St. John)

On our walk in Frick Park on 23 May, Charity and I saw many deer including an obviously pregnant doe who looked ready to drop twin fawns. We wondered where she would hide them now that the browseline makes it possible to see right through the woods.

This deer-browsed Japanese knotweed shows how little food remains for deer in Frick. Normally they don’t eat Japanese knotweed but with few native plants left they are hungry enough to try it now.

Deer damage on Japanese knotweed, Frick Park, 23 May 2023 (photo by Kate St. John)

In Schenley Park the color green extends to the rampant algae in Panther Hollow Lake. See last November’s article on why the lake has algae so often.

Algae in Panther Hollow Lake, Schenley Park, 26 May 2023 (photo by Kate St. John)

What birds will we see this weekend? Come to my Schenley Park outing tomorrow, 28 May, to find out.

(photos by Kate St. John)

Nowhere To Hide

Two deer at Schenley Park, 24 March 2023 (photo by Kate St. John)

17 April 2023

At the end of winter Pennsylvania’s landscape has very little cover yet wildlife still needs shelter, especially from bad weather. Normally birds and animals would hide in thick bushes and shrubs but the deer population in Schenley Park is so high that they’ve denuded the thickets, including bush honeysuckle, even though it provides them with good shelter and is not a favorite food.

Without cover the deer were easy to see in Schenley Park’s barren woods in late March. The deer pictured below was camouflaged in plain sight until it moved.

One deer camouflaged on barren hillside, Schenley Park, 24 March 2023 (photo by Kate St. John)

Evergreen bushes could provide shelter but the yews have been browsed literally to death as the deer population has grown exponentially in Schenley in the past couple of years. The white backdrop at Frick Fine Arts building shows the damage typical of all yews near the park.

Deer damage on yews at Frick Fine Arts building, Univ of Pittsburgh, 17 Feb 2023 (photo by Kate St. John)

Now that the honeysuckle has leafed out it’s obvious that deer have eaten their own shelter. You can see straight through these bushes at ground level.

Browseline on honeysuckle, Trough Trail Frick Park, 13 April 2023 (photo by Kate St. John)

The effect of deer browse is also starkly obvious at Frick Park’s deer exclosure at Clayton East. The slideshow below gives west and north views of the fenceline, the plants growing inside the exclosure (I took a photo through the fence) and the barrens outside the fence. (I pivoted in place to show inside/outside.)

Ground-nesting birds can make a well hidden nest inside the exclosure but not outside.

The deer have eaten their own shelter as well as that of birds, rabbits and other animals in Pittsburgh’s city parks. There is nowhere to hide.

(photos by Kate St. John)

More Deer, More Ticks, More Lyme

Deer in Schenley Park, Aug 2022 (photo by Kate St. John)

20 March 2023

Black-legged tick season is here again and with it comes the threat of Lyme disease. We now find ticks in neighborhoods where they never used to be and white-tailed deer are the reason why. More abundant deer mean more ticks. More abundant ticks mean more Lyme disease. Though deer themselves don’t spread Lyme disease they have an effect on its abundance. Let’s examine the Deer, Ticks, Lyme connection.

Lyme disease is a debilitating illness caused by a bacteria (Borrelia burgdorferi) that’s transmitted by the bite of a black-legged tick. 

Black-legged ticks (Ixodes scapularis and Ixodes pacificus) have a two year life cycle as egg, larva, nymph and adult. At each stage the tick must drink a blood meal to transition to the next one — from larva to nymph, from nymph to adult, and from adult female to produce eggs. (Note: Ticks eggs do not carry the Lyme bacteria.)

Chart of black-legged tick life stages (image from Wikimedia Commons)
Chart of black-legged tick life stages (image from Wikimedia Commons)

Larval ticks are so tiny that their normal blood hosts are small animals and birds including the white-footed mice, chipmunks, short-tailed shrews and masked shrews that are responsible for infecting 80-90% of ticks. Nymphs and adults are large enough that they can also feed on humans and deer.

Black-legged tick life cycle (diagram from CDC enhanced with life form names)

When a tick bites a host and sucks its blood it takes up the host’s blood and transfers some of its own body fluids into the host. If the host is infected with the bacteria, it infects the tick. If the tick is infected, it infects the host.

Deer cannot transmit Lyme to ticks because they’re never infected by it (lucky them!). Deer are not to blame for spreading Lyme. However deer are key to the black-legged ticks’ reproductive success.

Deer are the adult ticks’ preferred host and their long distance transport system. Deer bodies are the place where adult ticks meet and mate in the fall. After mating the male dies but the female lives on. She sips a last blood meal, then drops off to the ground and hides in leaf litter while her body develops eggs over the winter.

Adult ticks meet in the fall during the rut while deer are moving around a lot. Bucks average 3-6 miles per day but may travel as much as 10-20 miles in search of does. Does may travel to meet or evade them.

Deer in western Pennsylvania (photo by Steve Gosser)

Meanwhile ticks are along for the ride. When a pregnant female tick drops off after her last blood meal she may be 3 to 20 miles from where she started and she’s carrying 1,000 to 3,000 eggs that she’ll lay in the spring.

In places with overabundant deer moving into new areas, as is happening in Pennsylvania, we find an abundance of ticks where they’ve never been seen before. Pennsylvania also has the highest number of Lyme disease cases in the U.S.

Deer are not the reservoir for the Lyme disease bacteria but in places with too many deer there are too many ticks. More ticks mean more Lyme disease.

Deer cross the road in Schenley Park, July 2020 (photo by Kate St. John)

For more information check out these resources:

p.s. There’s also a flu-like disease, called babesiosis, that’s carried by black-legged ticks and is now gaining momentum. Uh oh!

Seen This Week

Flowering cherry, Pittsburgh, 1 March 2023 (photo by Kate St. John)

4 March 2023

This week the weather stayed above freezing with an extraordinary high of 72F on 1 March. The plants and trees responded by bursting into bloom and leaf. Pictured here are:

  • A flowering cherry tree in Shadyside, 1 March
  • Coltsfoot in bloom at Moraine State Park, 1 March
  • Hairy bittercress blooming in Shadyside, 2 March
  • London plane tree seed balls disintegrating (a spring thing), 27 Feb
  • Honeysuckle leaf out, 2 March.

A week ago my photos of blooms, buds and leaves were 4 weeks earlier than last year. When I get a chance I’ll see if spring is still running four weeks ahead of schedule.

Coltsfoot blooming, Moraine State Park, 1 March 2023 (photo by Kate St. John)
Hairy bittercress blooming, 2 March 2023 (photo by Kate St. John)
London plane tree seed ball disintegrating, 27 Feb 2023 (photo by Kate St. John)
Honeysuckle leafing out, 2 March 2023 (photo by Kate St. John)

Now that the plants are waking up for spring Pittsburgh’s deer (over)population is finding more to eat. In front of Phipps’ Botany Hall I found a side-by-side example of yews, a favorite deer winter food, protected and unprotected from deer browse. One bush has no protection, the rest were wrapped in plastic fencing(*). You can already see the difference.

(photos by Kate St. John)

(*) The protected yews were wrapped on 15 December 2022 so, at the time of the photo, the unprotected yew was showing 10.5 weeks of deer browsing.

The Forest Lives in Mortal Fear of Its Deer

Buck browsing a tree in Schenley Park, August 2022 (photo by Kate St. John)

18 January 2023

I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.

Aldo Leopold, A Sand County Almanac: “Thinking Like A Mountain”

Aldo Leopold (1887-1948), quoted above, was a writer, philosopher, forester and conservationist. In the early 1900s he participated in a project to eradicate wolves from the American West. Back then it was thought that the absence of wolves would be great for our range cattle but no one considered what would happen to the landscape without the apex predator. Thirty years later Leopold wrote about it in A Sand County Almanac. We see the same results in Pennsylvania and in Pittsburgh’s parks today.

  • In the absence of hunters (wolves) the deer proliferated.
  • Deer still ate what they always ate, but the higher population consumed so much more.
  • The deer’s favorite food plants disappeared first; all new growth was consumed. The deer covered more ground and ate less favored plants.
  • After a couple of decades with constant browsing and so many plants missing, the landscape cannot regrow itself. The range failed within 20-30 years.

It’s not the mountain rocks that are afraid of deer. It’s the forest that fears for its life because deer are its predators.

Doe and fawn browsing on a tree (photo from Wikimedia Commons)

When the deer population is in balance with the habitat, the forest is fine. When the population is too high the forest shows signs of distress on its way toward failure including browse lines and small bonsai-like trees, as seen in Schenley Park below.

Deer damage: Browseline in Schenley Park, Sept 2022 (photo by Kate St. John)
Bonsai-like deer damaged sapling, Schenley Park, Oct 2022 (photo by Kate St. John)

In Riverview Park deer overpopulation has encouraged the proliferation of invasive Asian jumping worms (Amynthas agrestis) and led to a host of other problems including erosion, described by Mark Kramer in How One Park’s Ecosystem — and Maybe its Legacy — Is Eroding Away.

Amazingly, it all started with the decision to remove an apex predator. We humans are the reason why there are too many deer and, so far, we haven’t had the will to reduce their population to a sustainable level.

In the meantime the forest is afraid for its life.

(photos by Kate St. John and from Wikimedia Commons)

Deer Density at a Glance

Tall columnar arborvitae along an alley in Kutztown, PA, 27 Nov 2022 (photo by Kate St. John)

12 December 2022

At Thanksgiving in Kutztown, PA I was stunned to see a solid wall of arborvitae bordering a neighborhood. In Pittsburgh’s East End, arborvitae is always bare from the ground to 4-5 five feet up, eaten by our overpopulated deer. Here’s a row of arborvitae at Schenley Park golf course.

Deer damage on arborvitae at Schenley Park golf course, 11 Dec 2022 (photo by Kate St. John)

Why didn’t deer browse the Kutztown trees? My guess is that they are the Green Giant variety of Western arborvitaes. Davey Tree explains:

Deer don’t care for Western arborvitaes, like green giant, steeplechase or spring grove. So, if you plant these, they may leave them alone.

Though, when deer are starving, they become less picky and will eat almost anything, including those deer-resistant arborvitaes. If deer are a big problem in your yard, avoid arborvitae altogether. Stop Deer from eating Arborvitae trees (even Emerald Green)

There are so many deer in Pittsburgh that indeed they eat almost anything. They even nibble on poisonous milkweed!

Kutztown has far fewer deer per acre.

The trees show deer density at a glance.

(photos by Kate St. John)

The Largest Living Organism is Dying of Deer

Pando in October snow, 2021 (photo by Beth Moon via Flickr Creative Commons license)

29 November 2022

In 1976 Jerry Kemperman and Burton Barnes discovered that 106 acres of quaking aspens (Populus tremuloides) in the Fishlake National Forest of Utah were actually all the same male plant, one root with thousands of suckers that grew into trees. It came to be known as Pando — “I spread.”

Quaking aspen, Pando, in fall (photo from Wikimedia Commons)

Pando weighs 6,600 tons making it the heaviest known organism on Earth and it is very old, though no one is sure whether it’s 10,000 or 80,000 or even a million years old.

Aerial image of the location of the single aspen tree, Pando (highlighted in green) at Fishlake National Forest, Utah (photo from Wikimedia Commons)

However, almost as soon as Pando was discovered researchers found that sections of it were not rejuvenating because new sprouts were being overbrowsed by deer. In that part of the U.S. the species is mule deer (Odocoileus hemionus).

Mule deer in Colorado (photo from Wikimedia Commons)

So they fenced it — twice — one fence in 2013, another in 2014.

Map of 2018 Pando study partially funded by U.S. Bureau of Land Management, Grant/Award Number: L21AC10369 (map downloaded from Wiley Online Library)

Then in 2018 Paul Rogers and Darren McAvoy of Utah State University conducted a followup study sampling Pando’s health inside and outside the deer exclosure fences and concluded that the fencing was not working.

According to September 2022 Sci.News “The unfenced areas are experiencing the most rapid aspen decline, while the fenced areas are taking their own unique courses — in effect, breaking up this unique, historically uniform, forest. … Fencing alone is encouraging single-aged regeneration in a forest that has sustained itself over the centuries by varying growth.”

“One clear lesson emerges here: we cannot independently manage wildlife and forests.”

Sci.News, October 2018: Pando, World’s Largest Single Organism, is Shrinking

Aldo Leopold’s experience in his early career when he worked to eradicate wolves from the American West changed his perspective on trees and deer. At one point he shot an old female wolf and was there to see the green fire go out of her eyes as she died. He wrote …

I thought that because fewer wolves meant more deer, that no wolves would mean hunters’ paradise. But after seeing the green fire die, I sensed that neither the wolf nor the mountain agreed with such a view.…

I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer. And perhaps with better cause, for while a buck pulled down by wolves can be replaced in two or three years, a range pulled down by too many deer may fail of replacement in as many decades.

Aldo Leopold: Sand County Almanac, “Thinking Like a Mountain”

Pando’s days are numbered because new trees are not growing up to replace the old ones. This is how a forest dies.

(photos from Wikimedia Commons, map from Wiley Online; click on the captions to see the originals)

November Deer in Pittsburgh

Doe on the trail in Frick Park, 10 Nov 2022 (photo by Charity Kheshgi)

13 November 2022

It’s mid November and the rut is at its peak in Pennsylvania. Bucks sniff the air for females in estrous (flehmen), chase does in heat, and hide with them in thick cover to breed repeatedly. Some run into traffic, including yesterday’s road-killed 6-point buck in Schenley Park. Meanwhile birders in Frick Park are seeing all of this up close. Very close.

On 10 November Charity Kheshgi and I encountered a group of five. Two does and an 8-point buck were hiding in a thicket when a 4-point buck walked onto the trail behind us, sniffed the air and looked down at the females. Meanwhile another doe (at top) walked onto the trail ahead of us. This could have been dangerous for the two of us. Fortunately the deer did not view us as competitors.

4-point buck on the trail looks down at the 8-point and two does, 10 Nov 2022 (photo by Charity Khseshgi)

The 8-pointer was hard to see in the underbrush but he resembled this 10-point buck Mike Fialkovich saw on 5 November that appears to be flehmening.

10-point buck in Frick Park, 5 Nov 2022 (photo by Mike Fialkovich)

Deer are a prey species, alert to the presence and intent of predators. “Is the predator here? Is it hunting?” And they move to locations of least danger. We see them up close in Frick Park because they have learned that humans in Pittsburgh’s city parks are not dangerous even during hunting season.

Meanwhile, hunting is currently in progress statewide and it’s good to be aware of it. We have so many deer in our area — Wildlife Management Unit (WMU) 2B — that hunting lasts longer here than in most of the state.

Map of Pennsylvania WMUs from PA Game Commission

Here’s a quick summary of deer hunting times and types, now through January, in WMU 2B both Antlered and Antlerless unless otherwise noted.

  • now – Nov. 25, including Sundays Nov. 13 and Nov. 20, WMU 2B: Archery
  • Nov. 26 – Dec. 10 including Sunday Nov. 27: Statewide Rifle (“Regular firearms”)
  • Dec. 26 – Jan. 28, 2023, WMU 2B:
    • Archery
    • Flintlock
    • Extended Rifle season (Antlerless only).
Wear Orange and be alert for hunters! Note hunting on three Sundays in November.

p.s. When you’re on the road, watch for deer running into traffic, especially at dusk.

(photos by Charity Kheshgi and Mike Fialkovich, WMU map from PA Game Commission, calendar marked up from