Frogs in Winter

This is another look at how some species survive through the winter. Previously, we looked at birds, moths, and bear cubs. Today, we're thinking about how frogs make it through winters in NJ when their watery habitats are frozen.

Many frogs spend their entire winter under ice, essentially looking like living "underwater rocks."  Some species of frogs are at the bottom of frozen ponds and slow-moving rivers. However, they don’t all use the same survival strategy.

Here are three survival strategies.

Since the surface is capped with ice, frogs can't exactly pop up for a gulp of air. Instead, they rely on cutaneous respiration. They absorb the limited oxygen dissolved in the pond water directly through their skin. To make this work, they have to stay very still to keep their oxygen demand to a bare minimum.

For most aquatic frogs—like Bullfrogs and Northern Leopard Frogs—the goal is to stay cold but not frozen. They sink to the bottom of the pond. They don't burrow deep into the mud (like turtles do) because they need to stay in contact with the oxygenated water. They spend the winter in a state called brumation, where their heart rate slows to a crawl, and their metabolism almost stops.

If you see a frog near the surface or under some leaf litter, that’s likely a Wood Frog. These frogs are the overachievers of the winter world. They don't usually stay underwater; they stay on land under leaves. They actually freeze solid. Their heart stops, and their breathing ceases. They use a natural "antifreeze" (glucose/sugar) to keep their cells from bursting. When spring hits, they "thaw" out and hop away like nothing happened.

The biggest threat to a frog under the ice isn't the cold—it's the oxygen. If a pond is shallow and covered in thick snow, sunlight can't reach the plants to produce oxygen. If the oxygen in the water runs out before the thaw, the frogs (and the fish) won't make it.

Bear Cubs in Winter and Spring

We have a few months before we are going to see any bear cubs wandering around New Jersey. But on another blog, I wrote about the February Full Moon as being the "Bear Cub Moon."

It may seem like some kind of magic to most people that a mother bear goes into a hole she dug in the ground in the fall and emerges in the spring with a couple of new, fuzzy, walking cubs. This magic trick is some very amazing biological engineering. 

The hidden-from-view birth of a bear cub is fascinating. Bears actually mate in the late spring or early summer, but the mother doesn’t technically become pregnant right away. Through a process called delayed implantation, the fertilized egg remains as a tiny ball of cells (a blastocyst) floating in her uterus for months. 

It only implants and begins to grow in the late fall, and only if the mother has gained enough weight. If she didn't eat enough berries or fish to survive the winter, her body would simply reabsorb the embryo, ensuring she doesn't try to raise cubs she can't support. 

Cubs are typically born in January or February, right in the heart of winter. While we call it hibernation, the mother isn't "dead to the world." She is in a state of light dormancy. She is alert enough to wake up, give birth, lick the cubs clean, and nudge them toward her belly to nurse. 

Because the cubs are so tiny, labor is relatively quick and much less physically taxing than it is for humans. 

Newborn cubs are incredibly primitive—often described as "fetal-like." They weigh less than a pound (about the size of a stick of butter or a teacup) and are born blind, nearly hairless, and totally helpless. 

newborn bear cub      nps.gov

Because they are so small, researchers often call the time in the den an "external pregnancy." Once the cub is born, it soon begins to nurse. A newborn cub’s physiology changes from one that couldn’t survive on fat in the womb to a system that can better metabolize fat. The mother provides all the nourishment that the cub needs, and the den offers warmth and protection. 

For the next several months, the den acts as a surrogate womb for the rapidly growing cub. Instead of growing inside the mother where they would drain her protein and mineral stores, they grow outside her body, fueled by her fat-rich milk.

Perhaps, the most amazing part is how they survive for months without a snack or a bathroom break: Mother bears produce milk that is incredibly high in fat (up to 30% fat), which allows the cubs to grow from less than 1 pound to about 5–10 pounds by spring. 

The mother bear does not eat, drink, urinate, or defecate for months. Her body is a closed loop; she recycles her own urea (waste) back into protein to maintain her muscle mass while she sleeps. 

The den acts as a giant incubator. The mother curls around the cubs, using her body heat to keep them at a steady temperature while the snow piles up outside.

Fish for Trout Year-Round

As the weather gets colder and the days grow shorter, don’t put your rod and reel away just yet! Winter trout fishing can be incredibly rewarding. So, if you haven't tried targeting trout during the winter, this seminar is perfect for you!

Join NJDEP Fish & Wildlife's Fishing R3 program for a FREE Winter Trout Fishing Seminar. You'll learn how to effectively target trout during the winter months and get recommendations on gear.

Saturday, December 6, 2025 - 9:30 a.m.
Ocean County Library - Jackson Branch, Jackson Township

Registration is required. Limited space is available.
Registration deadline is December 4, 2025, or when full.

Ice Fishing Seminar Register by November 2

Personally, I hope it's too early for ice to be forming on lakes, ponds, or even on puddles near my home, but it's not too early to join NJDEP Fish & Wildlife's R3 Fishing Program for an introductory Ice Fishing Seminar. 

This free seminar, scheduled early in November, is designed to provide an informative and welcoming environment to prepare you for ice fishing. This program is open to experienced anglers, 18 years and older, who will be introduced to the sport of ice fishing by outdoor and ice fishing enthusiast David Alexander. David is a lifelong educator, naturalist, and conservation biologist. This seminar will cover ice safety, staying warm and dry, targeting specific fish species, depth maps, ice fishing equipment, knots, bait selection, and techniques. Through lecture, demonstrations, and hands-on components, you'll leave the workshop prepared to hit safe ice - if and when New Jersey gets any this winter.

Sunday, November 16, 2025 from 9:30 a.m. to 12:00 p.m.
at the Hackettstown State Fish Hatchery
Deadline to apply November 2, 2025.

Information & Register

Thermonasty for Winter Protection

 

Rhododendron thermonasty

During particularly frigid days, the evergreen leaves of Rhododendron maximum display a unique trait known as thermonasty. In essence, the leaves are a type of natural thermometer. When temperatures dip below freezing, leaf margins curl inward causing the leaf to roll up and droop. Leaves are most tightly curled when temperatures are below 20 degrees.

Thermonasty is a useful adaptation that provides several important benefits. Rhododendron leaves are particularly susceptible to damage from desiccating winter winds—tightly curled leaves ensure surface area is reduced, thereby mitigating this threat. Additionally, during periods of extreme cold leaves are more prone to damage from the sun. Again, a reduced surface area helps to protect the leaves. 

Broad leaves positioned in a way to maximize sunlight collection is a liability when it comes to snow. Narrow, drooping, needle-like leaves help shed snow that could otherwise accumulate and break branches.

Even in late spring, some species of tulips close their flowers in response to cold temperatures at night and open them during warmer days. Similar to tulips, certain crocus species also exhibit thermonastic movements, closing their flowers in cold temperatures and opening them when it is warmer.

Sowing Seeds in Winter

Winter sowing is a method for growing native plants that involves planting seeds outdoors in containers during the winter. It mimics the natural process of stratification, where seeds experience the cold and precipitation of winter, followed by warmer temperatures in spring. This process is critical for breaking dormancy in many species, especially wildflowers and sedges.This process is called cold stratification. Nature does it, well, naturally. People can recreate this in controlled conditions.

I consider myself to be a pretty good gardener - not a master - but I'm new to cold stratification. That probably explains why some seeds that I planted in early spring never sprouted. 

Native plants give food and shelter to bugs and birds, and don't need much to thrive. They stay dormant over the winter, then germinate at the right time in the spring. 

Mixing seeds with barely damp sand, vermiculite, or peat moss is the start. Some people put this damp seed mixture in a container in the refrigerator, but I was told by some other wiser gardeners that it's better to let nature do the job.

The seeds of some species go into a period of embryonic dormancy and often will not sprout, or will have a poor germination percentage, until this dormancy is broken. Other species have seeds with a very hard seed coat, and exposure to the moist cold helps break down this shell for easier germination in spring. 

General Directions
Use containers with drainage holes that are about 3-4 inches tall and have a clear top with ventilation holes. I see that people cut old plastic milk jugs in half, sow seeds and reattched with duct tape. Leave the cap top open.
Cover seeds with a layer of sand to hold seeds in place from rain. Freezing and thawing will works the seeds down as it does with seeds that plants self-sow. I'm using a window screen over them in an old cold frame.

Getting this done before a snow is also recommended.

When they naturally sprout in spring, treat them as you would any seedlings. I worried that if they sprouted too early, they would die in a cold snap but others have told me that nature will take care. Still, I'll probably add some protection in early spring. Keep the seedlings watered throughout the growing season. Plant them directly into the ground or move them into regular containers.

What species should you winter sow? My first thought was milkweed which I planted last spring and had lousy results. You can find lists of species but here is a start: Asclepias, Aquilegia, Amsonia, Aruncus, Baptisia, Chelone, Echinacea, Eupatorium, Eutrochium, Geranium, Spicebush Mountain Laurel Coastal Pepperbush New England Aster White Wood Aster Zigzag Goldenrod New York Ironweed Eastern Bluestar Blue Lobelia Butterfly Weed Swamp Milkweed Common Milkweed Foxglove Beardtongue Wild Indigo. 

More at wildrootsnj.com/blog/sowing-native-seeds-in-winter

How Birds Adapt to Winter

 

The Tree Swallows Tachycineta bicolor shown above huddling on a branch during a snowstorm are demonstrating one way that birds stay warm during the winter. 

Of course, some birds move to warmer climates in winter, but many birds stay in New Jersey all year. How do birds can stay warm in the cold winter months? An article at fws.gov discusses ways that they cope. Here are some excerpts. 

Just like people, birds shiver to stay warm. Birds have much higher metabolic rates and burn more energy to stay warm than we do. Black-capped chickadees weigh less than half an ounce and can maintain a body temperature of 100 degrees Fahrenheit - even when the air is 0 degrees! They also have great insulation, stay active, and remember where they store their food. 

Like human homes, birds use insulation. Whether fat, fur or feathers, insulation matters for most cold-weather animals. And like many humans, cold-climate birds pack on body weight in the fall. People wear insulating clothing. Birds also trap pockets of air around their bodies, which requires having clean, dry and flexible feathers. 

People cuddle for warmth and so do small birds in shrubs, vines, evergreen trees, branches and wires.  Cavity nesters like nuthatches, titmice and downy woodpeckers use tree cavities and nest boxes to stay warm. Larger birds like American crows and ring-billed gulls are also known to flock together for warmth.

I hate having cold feet in winter. Birds hate it too and waterfowl species circulate blood through a countercurrent heat exchange, isolating the blood that flows in their legs rather than circulating it throughout their entire bodies. This helps to keep their body temperatures higher. Birds also have specialized scales on their feet and legs that help minimize heat loss. Many ducks, geese, pelicans, gulls and swans further conserve body heat by standing on one leg or even sitting down. Some birds will also tuck their bills under their back feathers to keep it warm and increase breathing efficiency by utilizing warmer air.

People can help too. Providing high-energy foods like suet, peanuts and black oil sunflower seeds and water year-round is critical. If that feeder you filled all summer goes empty in winter, birds who became used to feeding there are at a loss. A heated bird bath or one that you regularly de-ice and refill with clean water is also important to help keep birds hydrated. 

Photo By: Keith Williams, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0

Wildlife Sightings and Identification

A mountain lion (cougar) not in NJ but in Illinois. 
It's a big cat and you would probably know one if you saw it nearby.

One of the most frequent comments and emails I get here is about sighting wildlife and about identifying wildlife. Occasionally, it will be a bird or invertebrate, but more often it is something more exotic - a mammal that lives in NJ or one that, as far as we can confirm, does not live in our state.

With the weather warming and COVID restrictions lifting, I have had a flurry of comments and emails of this type. I try to respond to all of them. I make no claims to expertise. I'm not a biologist, just a longtime volunteer in environmental programs for the state and other groups.

Our post "Is That a Mountain Lion I See Wandering New Jersey?" has gotten a lot of attention and comments from people who maintain that they have seen a mountain lion in New Jersey. We still have no confirmation of any in our borders. Unfortunately, reports such as the two below that came in recently, are almost never accompanied with any photo evidence of the animal, tracks, scat etc. 

I have seen 3 in the 20 years of living in Newfoundland, NJ. Two were in my yard which borders Watershed property and one on route 23 at the Oakridge Rd intersection. They are here!

and

Mountain lions are ambush predators. You don’t just look outside and see them. They are most definitely here in north jersey as I have seen a handful over the course of years.

On the "Otters in New Jersey" someone said, "Yeah I saw like four or five otters one time, in Holland township NJ, in a small stream while I was fishing."  That is certainly possible. But I have also had people send photos of muskrats and others and say it was an otter, fisher or even a beaver. Those animals don't really look the same but they are similar and going in or out of the water quickly might be tough to identify on the run. 

I also got an email with some snow photos that I'll assume were taken either some months ago or perhaps not even in NJ.

The email said"

Just stumbled across your site and thought maybe you can help me. After a snow this year I went for a walk in the words near my home and came across these fresh tracks. Scary looking! Any idea what these could be from? I certainly don’t want to be alone with whatever made them I don’t think! But would really like to know.

Knowing the location and date would be very helpful but it was good that the person included a hand to give a sense of size.

* A follow-up email told me that the tracks were in Sterling Forest right at the border of NY/NJ in January after a big snowfall right around Ringwood Manor in northern NJ. 

Tracks in the snow are notoriously difficult to identify unless they are very fresh. Melting and wind can change track. The writer sounds a bit frightened by the size of these tracks. Maybe they are thinking "bear."

I had several people look at the tracks and they pointed out that a smaller animal can leave big tracks in the snow because of dragging their legs, hopping, running, or even from a tail. Two people said they thought this might be a rabbit, which is probably disappointing to the email writer. Sometimes the front and rear feet will land in almost the same place and make a "large" track (true for rabbits). 

Here are two sets of bear tracks.

These are some very clear tracks showing five toes/claws. Easy to identify.

In this late in the day photo, tracks that are known to be a bear almost appear
to be human prints as the details have become lost.

It would probably surprise many people that New Jersey has a robust black bear population. We estimate there are about 3400 bears in the northwestern part of the State and bear sightings have been officially reported in all 21 counties.

Look at this strange set of tracks.

photo: animaltrackersofnewengland.blogspot.com

This rather artistic-looking set of tracks is identified by another blogger as
the trail of a bobcat dragging a rabbit.

So who left those tracks in the two photos emailed to me? I honestly cannot make a positive identification. Perhaps, a reader will add a thought. And it's entirely possible that someone will think it's a mountain lion, the Jersey Devil, or Bigfoot.