Back from the Brink

Two large rounded lumps ambled onto the edge of my yard. I squinted to make out what they were.

“Turkeys!” my daughter squealed, as three, and then five more joined the first two. Like miniature dinosaurs with all the time in the world, they meandered, pecking here and there, and scratched at the ground. I grabbed some sunflower seeds, my daughter,  and my camera, and walked into their midst. Clearly used to being the big kids on the block, these birds showed no concern over having a human in their crowd.

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Perhaps it was this trust that nearly led to their extinction by the early twentieth century. Turkeys are native to the U.S. and were Benjamin Franklin’s choice to be our national bird. They were so plentiful in the days of colonial history that, like the carrier pigeon, people thought they could never run out. Their carefree and slow movement, coupled with their meatiness made them a favorite food source.  

Throughout the 19th century turkeys were hunted relentlessly year-round. No seasonal restrictions or limits existed on how many could be taken. Together with the loss of their woodland habitat as forests were cleared for human habitation, turkeys hovered on the brink of extinction by the early 20th century. From a pre-colonial population estimated at ten million, by 1910-1920, there were only about 200,000 remaining.

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This tom is strutting his stuff to impress the ladies. He blows up his iridescent feathers, fans his orange barred tail, and lifts his head high to show off the bright blues and reds on his head and neck. I’m impressed!

So what saved the turkey from following the route of the carrier pigeon to the annals of extinction?

Serendipity and human effort. The Great Depression and the Dust Bowl forced many farmers to abandon their farms and move to urban areas in search of work. As they retreated, the lands they left reverted to native habitat. Yet, there were so few turkeys left that they could not repopulate these growing woodlands. At least 16 states had completely lost their native turkey population. (Source: “Americans Once Almost Ate Wild Turkeys Into Extinction,” The Dodo, November 25, 2014) Efforts to catch and release turkeys, or to incubate eggs in the 1940s were a failure. What finally turned things around for the wild turkeys was the invention of the net cannon, which made capturing them much easier.

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Net cannons like this enable conservationists to capture a large number of birds at once.

Large numbers of turkeys could be easily captured with these nets and transported as a herd to states with low or no turkey populations. Their recovery is one of American conservation’s greatest success stories. The organization behind this success is the National Wild Turkey Federation, a nonprofit representing hunters, and dedicated to protecting habitat for that purpose. A half century after their near-extinction, there are now over 7 million wild turkeys roaming America. It is remarkable how much can be done to save endangered species when there is a will to do it.

Unlike vultures, turkeys don’t eat carrion. The absence of feathers on their head is related to courting. When turkeys are trying to attract a mate, the exposed skin flushes with blood and its bright blues and reds advertise their interest.
Unlike vultures, turkeys don’t eat carrion. The absence of feathers on their head is related to courting. When turkeys are trying to attract a mate, the exposed skin flushes with blood and its bright blues and reds advertise their interest.
When disturbed, turkeys are more likely to run than to fly. They can run up to 25 m.p.h. Maybe that’s why Mamaroneck calls its race the Turkey Trot! At night turkeys fly up to roost in trees, and if you are lucky you can spot an entire crop of turkeys in one tree.
When disturbed, turkeys are more likely to run than to fly. They can run up to 25 m.p.h. Maybe that’s why Mamaroneck calls its race the Turkey Trot! At night turkeys fly up to roost in trees, and if you are lucky you can spot an entire crop of turkeys in one tree.

Baby, it’s cold outside

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Last week the winds howled and temperatures fell below freezing. Trees and branches cracked and sprawled across the ground. Leaving my house, I pulled my coat tight, drew my hat over my face, and in my fuzzy boots scuttled the 15 feet to my car. I blew a gust of frozen breath in the safety of the front seat. Then I looked out and saw a dark eyed junco, a tiny songbird pictured above, sitting on a branch, calm as can be.

How can a wee bird weighing no more than three pennies spend 24/7 in such cold temperatures without freezing to death?

Down, down, down

That jacket or blanket that you may have for extra cold days is stuffed with down for a reason. Unlike the long flight feathers on a bird’s wings and tail, the down feathers are short and can be fluffed up. This fluff creates air pockets that trap the warmth escaping from the bird’s body. The specialized down feathers can keep a bird’s body temperature at 104 degrees even in freezing weather!

Birds also undergo a fall molt in which they grow up to fifty percent the number of feathers on their body for greater insulation. That fluff is what makes these tiny birds look round as tennis balls in winter.

Have you ever seen birds poking their beak into the base of their tail, then rubbing their beak all over their bodies? They are collecting oil from the uropygial gland and spreading the oil over their feathers. Not only does the oil keep feathers preened and clean, but it also adds a weatherproofing layer that keeps them from getting wet. Can you even imagine the misery of having wet feathers in winter?

Wait, what about my feet?

No matter how warmly I dress, my feet and hands are usually the first thing to freeze in winter. So how do those featherless, little reptilian bird feet stay warm in winter?

For one thing, those sinewy feet have very few nerves, which reduces the cold that the birds feel through their feet. The scales are specialized to minimize heat loss. Birds also take turns lifting one foot and tucking it into their feathers to warm it up, or crouching down over their feet to warm them. 

But they have another brilliant adaptation as well: rete mirabile, which is Latin for “wonderful net.” In the rete mirabile, arteries that carry warm blood away from the heart intersect with veins that carry cold blood from the feet. A heat exchange occurs, and the blood from the feet warms before reaching the bird’s heart.

rete mirabile
This drawing illustrates the process of rete mirabile, whereby vessels carrying cold blood from the feet intersect with vessels carrying warm blood from the heart.

And then there is shivering

Birds are warm blooded creatures and, through a high metabolism, maintain a body temperature at about 105 degrees Fahrenheit. How challenging it must be to keep such a high body temperature in extremely cold weather! When all else fails, birds will start shivering their powerful chest muscles. The pumping of their strong flight muscles sends blood and heat surging through the body. But this relief comes at a cost. Half the calories that a bird needs to survive a wintry day could be depleted in the act of shivering. A chickadee, for example, requires the equivalent of 65 sunflower seeds to survive a cold winter day. Food to replace those lost calories is scarce in winter. Most insects and trees are dormant.

Birds are highly resourceful creatures, and they have adapted to find sustenance in seemingly barren environments. They have exceptional eyesight, and can tease out tiny cracks in tree bark serving as insect hideaways. As gardeners, we can help them by not removing our dead plantings in the fall. Those browned flower heads can contain seeds and insects that sustain birds through the winter (see Hidden Provisions blog entry). And if you are feeling extra generous, you can fill a feeder with sunflower seeds or suet, and enjoy the feeding frenzy that ensues.

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Cardinal waiting for his turn at bird feeder

 

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“What are you waiting for?,” this female cardinal must be thinking.

 

 

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Joining the junco and sparrow for a sunflower seed snack.
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Red-bellied woodpecker snags a seed

 

 

 

 

Hanging On

Most winter trees fall into one of two categories we readily recognize. There are the deciduous trees, whose leaves fall off in winter, and there are the evergreen trees, who keep their leaves throughout the winter. But there are trees that don’t squarely fit into these categories.

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In the photo above, you are looking at an American Beech, which is a deciduous tree. And although its leaves have wrinkled and faded, they hang on tenaciously to the tree. Take a walk in the Sheldrake woods and you’ll notice them right away, like a ballroom of debutantes frozen in time, not ready to hang up their petticoats for the season.

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There is a name for what these trees are doing: marcescence, or the retention of dead plant organs. In deciduous trees autumn triggers a chemical change that makes the tree grow a layer where the leaf stems connect to the branch. This layer creates a separation between the leaf and the branch, and prevents water and nutrients from reaching the leaf. That separation, also known as abscission, is the reason leaves change color, shrivel, and fall off. But in marcescent trees such as oaks, beeches, and witch hazel, even though the abscission layer forms, and the leaves shrivel and fade, they do not fall off.

Why? Why would a tree want to hold on to dead leaves that can no longer produce food?

This is one of those delicious questions that we actually do not know the answer to. There are theories, but in the absence of sufficient testing, we cannot say which is correct.

Hypothesis #1: Protection from browsers

It is possible that marcescent leaves may provide cover for tree buds from large browsing herbivores such as deer or moose. Crumbly zero-nutrition leaves may provide a layer of deterrence, since animals would have to eat through the leaves to get to the nutritious buds and twigs they like to eat, if they can even see them through the leaves!

beech bud
This beech tree bud is protected by its tough wrapping and pointy tip, and is also tucked away between the tree’s dead leaves.

In support of this theory is that marcescent leaves are primarily found on lower branches and young trees, whose buds are within reach of browsers.

beech full
In the above follow the trunk of the beech tree with the marcescent leaves. You will see that all the leaves appear in the lower branches. The upper and middle branches are bare.

Hypothesis #2: Strategic decomposition

A second theory posits that there is an advantage to dropping the dead leaves in the spring, as new growth finally pushes off the old leaves. Marcescent trees such as beech and oak traditionally grow on infertile soil. It’s possible that by dropping the leaves in the spring, they will decompose at the time when the tree most needs the organic compost to spur new growth.

Personally I find this explanation less convincing, for it does not explain why only the younger trees or lower branches sport the dead leaves. Also, decomposition in winter is very slow due to the shorter hours of sunlight and the dormancy of many decomposers, so I am not certain there is much to be gained by waiting until spring to drop to the ground.

Hypothesis #3: Evolutionary vestiges

The first trees were all evergreens, keeping their waxy leaves through winter. As they succeeded and spread, they evolved to suit the different climates in which they found themselves. Some found it advantageous to shed their leaves over winter, to avoid freezing or depleting their nutrient store, and deciduous trees were born. It is possible that marcescent trees such as beeches and oaks are an evolutionary halfway point–deciduous trees that retain their (dead) leaves through the winter. Perhaps these clinging ghosts are an evolutionary vestige, like the human appendix or tailbone, which serves no function but has persisted over time. Lending support to this explanation is the fact that some beech and oak species are evergreens. The Southern Beeches are 43 species of evergreen trees and shrubs that until recently were classified in the same genus as beeches (They now have their own genus, Nothofagaceae, which translates to “bastard beeches.”). Their fossil record dates back to the Cretaceous period. Among oaks, the Quercus ilex is an evergreen.

What do you think? Which do you find most convincing? Whatever the explanation, take this time to walk in the woods and enjoy the rustle of the wind rattling these stubborn stragglers.