The Principles of Natural Selection as they apply to Baby Birds

Note: This show first aired July 25, 2015.

Natural selection is the mechanism by which evolution takes place, and by evolution, I mean the change in genetic material in a population over time. That change over time is thought to make populations more robust, more “fit”, fitness meaning more successful reproductively; and successful reproduction is the name of the game when it comes to life on Earth.

Darwin’s theory of evolution by natural selection is based on three simple premises: that more individuals are produced than can survive, that there is variation in the traits of those individuals, and that the individuals with the traits best suited for survival and reproduction in the environment will survive. The genes that code for the successful traits get passed on. Genes that code for less successful traits get passed on far less frequently, and eventually disappear from the gene pool. That is how over time, the genetic makeup of a population changes.

We’ve been talking the last couple of weeks about an ill fated pair of baby birds, they were discovered tumbled out of a nest that was blown out of a tree, and birds and nest were replaced into said tree as best an anxious adult and curious child could do. Upon first check up, the baby birds were discovered to be out of said nest again, and replaced a second time. Upon second check up, both babies were gone, as were the parents. In some ways the experience feels like failure, but as I talked about last week, the odds for those babies were never very good even in the best circumstances, which brings us to that first tenet of Darwinian evolution: more individuals are produced each generation than can survive. So why didn’t these birds survive? 

The second tenet of natural selection states that there is variation in traits among individuals in a population. Among all of the chipping sparrows in the northeast, some make very strong well protected nests, others make flimsier ones. Some choose nest sites out of the prevailing wind, others choose more exposed shrubbery. Nest building is a very instinctual behavior in birds (though there are studies that show that as some birds practice, their nests get better, indicating that there is a significant learning component to nest construction as well). The instinctual part of nest building results from genetics, some birds have genes that code for proteins that end up directing cells to do X, other birds may have genes that code for proteins that direct cells to do Y. If X causes the nest to be built in a very secure location, and Y causes the nest to be built in a more exposed location the genes have significant implications for the fitness of the individuals. Those birds may survive, but where they locate their nests impacts the survivorship of their young, and whether or not the genes of the parents get passed on into the chipping sparrow gene pool or not. If they can’t successfully reproduce because they keep building their nest in an unsuitable place, they are a genetic dead end, which brings us to Darwin’s third tenet of natural selection. Genes that code for successful traits get passed on, genes that code for less successful traits eventually die out.

There is one more factor beyond how successful or not the traits your genes code for are, and that factor is simple bad luck. Sometimes organisms are doing all the right things, have robust traits, and high survivorship, when bad luck strikes. In the case of birds, they could be in a tree that gets cut down, or in a tree that gets damaged by lightening or a falling nearby tree, things that don’t have anything to do with their nest location and building skills. And that is the other hard truth about natural selection, there is a large and strong random component to it. Just as the mutations that give the gene pool variation are random, so are the incidents of “bad luck” that can change the distribution of genes in a population without respect to their impact on fitness. These shifts in gene frequency due to bad luck (or being in the wrong place at the wrong time) are called genetic drift, and the smaller the population size, the bigger an impact it can have. 

The mechanism of natural selection cuts a broad and unforgiving swath through populations every reproductive cycle, and while there can be bad luck, there is rarely good luck. The modern human experience of the world is so different from this that it is hard for us to remember. In nature, the default is failure. Keep this in mind as you look around you and recognize what you see for what they are-the chosen few, the rare success stories amidst nearly infinite attempts at life.

References:

The basics of Darwinian evolution: https://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen/popgen5.htm

On birds, nests, instinct and learning—this well publicized study came out in 2011 and challenged the long held assumption that bird nest building is entirely instinctual http://www.sciencedaily.com/releases/2011/09/110925192704.htm

More about those chipping sparrow nests: http://www.allaboutbirds.org/guide/Chipping_Sparrow/lifehistory#at_nesting

Genetic drift: http://evolution.berkeley.edu/evolibrary/article/evo_24

First Year Bird Mortality

Note: This program first aired on July 18, 2015.

Today I have an update to the story I told last week. If you missed it, my niece and I recalled the experience of finding a bird nest that had been blown out of a tree. It was on the ground, and around it were the baby birds that had been in it. We put the birds back in the nest and put the nest back in the tree the best we could, hoping the parents, who were anxiously flitting around the tree chirping, would be able to resume their parenting duties. We realized that this was the right thing to do, even though emotionally it was really hard, our nurturing drive kicked into over drive and we just wanted to take the babies home to “save” them.  And I wish I could give you a happy ending to last week’s story, but the fact is, I can’t. When I went back the next day, the nest was empty, the babies gone, and the parents, if they were around, were silent. When my niece called later for an update, I had to tell her the truth. I was anticipating some melodrama, but instead she said so matter of factly “I kind of knew that was going to happen”, and that was the end of it.

You may wonder, as I have, if putting the babies back into the nest and leaving them was indeed the “right thing to do”. After all, even though we did the right thing, we left them with their parents, it didn’t work out. The reality is that even though they had the best chance of surviving under the care of their natural parents, that doesn’t mean that chance was very high to begin with. This is another one of those dirty secrets of nature that most of us never think about. Most things that are born don’t make it out of childhood. The average mortality for first year birds can be as high as 90%. For typical passerines or perching birds, juvenile mortality in the nest is around 50%, that is before the young even fledge. Nest predation and weather related accidents account for most of this mortality. Once the young fledge and eventually learn to take care of themselves, mortality pressure doesn’t let up but it changes form some what. Young birds aren’t as successful at feeding themselves, so starvation gets added to predation as another factor in first year bird mortality. Most of us, watching our back yard bird feeders, never have any idea the odds are so poor.

But what is the alternative? If a pair of robins in your yard has two successful broods a year (Robins are thrushes and will have a second and even occasionally a third brood in a single season if time allows), and each brood consists of 4 young, at the end of the season where there were 2 robins we now have 10. An environment that easily supported 2 robins may not so easily support 10. And what of next season, if all 10 of those robins were to survive and reproduce? The world would soon be flooded with robins, the environment denuded of all appropriate robin forage. It isn’t even a realistic scenario, and we all understand that. But in order to have the realistic scenario, a relatively steady state of robin population in our back yards, young robins die. Old ones do too, but robins are adapted to have more babies hatch than old birds dying, because the young are such easy prey. If you have many offspring, hopefully one will make it to old age.

Humans used to live this way too. When child mortality was much higher than it is now, women gave birth to many more children. As health care has improved and child mortality has dropped dramatically in most parts of the world, the number of children a woman gives birth to has dropped as well. We no longer have to hedge our bets like the birds do.

Most birds will try again and renest when they experience a nest failure, like those chipping sparrows at my neighbor’s house. There’s still a chance that we will see their young flying this summer, just not the young from that ill fated nest. And when I see an adult bird, I’ll see all of its nestmates now as well, the ones who pulled nature’s short straws, enabling life as we know it, to go on.

References:

Uncited but with interesting math: http://www.countrysideinfo.co.uk/bird_lifespan.htm

Uncited but good ideas (personal blog of a bird researcher) http://toughlittlebirds.com/2013/07/10/the-fledgling-problem/

Check out her entire blog, really nice stuff: http://toughlittlebirds.com/2014/05/30/helping-baby-wild-animals/#more-2653

http://toughlittlebirds.com/

The Junco study: http://www.jstor.org/stable/5000?seq=1#page_scan_tab_contents

The free shelf at my local academic library yielded a 1975 copy of Wallace and Mahan’s An Introduction to Ornithology 3^rd Ed, which has been a great source of foundational material!

What do do with a baby bird

Note: This program first aired on July 11, 2015.

This week's show featured my niece Caitlin as we described the experience of finding a bird nest on the ground one windy day, and then finding the baby birds that went with it. We talked about what we did and how it felt, and how doing the "right thing" was hard.

The internet is a great resource for leaning about what to do in that situation, if you go to a reputable site. The internet can also trip you up (as Caitlin said to me that night "the internet lies!"), so you have to be careful about who you listen to.

Some of the sites I used to figure out what to do are listed here:

http://audubonportland.org/wcc/urban/babybirds

http://www.birds.cornell.edu/AllAboutBirds/faq/master_folder/attracting/challenges/orphaned

 http://www.massaudubon.org/learn/nature-wildlife/birds/baby-birds-out-of-the-nest

There are lots of Wildlife Rehabilitators in Maine, but they don't all take birds (that requires a federal permit. If their listing says they don't have a permit, that means they can't take birds).

http://www.maine.gov/ifw/wildlife/pdfs/RehabersReport.pdf

The most well known bird rehab facility in Maine is Avian Haven in Freedom (Waldo County). http://www.avianhaven.org/

Remember, all migratory non game birds are protected by federal law. It is against the law to possess any bird or bird part (living or dead) without a federal permit!

Spring Bird Migration

Note: This program first aired on May 16, 2015.

 

Spring in Maine is such a delight. Every day brings a new sound, a new smell, a new sensation to be experienced. As I write this, yesterday I heard my first Black and White Warbler of the season, and today my first Black Throated Green Warbler. Each one of these little birds migrates to Maine from geographies further south. Black and Whites winter from Florida, through Mexico and Central America to Columbia and Ecuador. The Black Throated Greens winter in Cuba and the island of Hispanola, along the Yucataan peninsula and Honduran highlands,  and in the northern most part of South America. Both of these birds, like so many others, make their way from their warm wintering grounds to mid and high latitude forests, for the express purpose of breeding. The mid and high latitude forests, just awakening from winter’s dormancy, offer a bonanza of resources to these migrants, from an explosion of nutritious insects, to nesting sites and lowered nest predation pressure. So these little birds arrive as ready for spring as you or I.  

The difficulties of migration are many. These birds oxidize their body fat, muscles and internal organs for energy, and breathe so rapidly that they easily dehydrate, something that can become the limiting factor in length of migratory flight. The means by which birds navigate are complex, numerous and not entirely understood. What we know for certain is that human infrastructure confuses some migrating birds; bright lights and tall buildings have killed thousands of them.  Migration is hard and dangerous and birds can suffer high mortality if they are in the wrong place at the wrong time.

Which brings me to my main point. When I am roused from sleep by the sound of a new bird song coming in my window on a spring morning I have to remember not just the excitement of hearing a new bird, but also deep humility in the face of that bird’s accomplishment. That new warbler I hear flew all night to get here. All of these song birds are nocturnal migrants, so not only did they fly all the way from Florida or further, they did so at night, while I was sleeping. During the day they rest and forage, and follow environmental cues as to whether it is warm enough to keep going (the cold gray period of a couple of weeks ago surely slowed down the East coast migration into New England, now that the sun is out and the weather warm, the birds have started showing up again). They fly at night for a number of good physical reasons; they get all day to eat before they have to fly again which can shorten their overall migration time. There is less wind and turbulence at night, so the flying is easier. The air is cooler so the birds lose less water, and because it is cooler, the relative humidity is higher which leads to higher density air. The higher the air density the easier it is to generate lift, a key component of flight. Night flight has many benefits going for it.

The most important reason for birds to migrate at night though, at least in my mind, is because they are trying to avoid predation. And what preys on little birds flying thousands of feet up in the sky you might ask? Other birds. Yes, the dirty secret of the avian world is that big birds eat small birds, and not just occasionally. The Accipiters, a group of hawks that includes Copper’s Hawks, Sharp Shinned hawks and Goshawks, and the Falcons a group that includes Merlins, Kestrels and peregrine falcons, are all birds that prey primarily on other birds. This predation pressure was strong enough, that when combined with the all the other positive attributes of night migration, yielded enough selective pressure to cause songbirds to evolve to migrate in the dark. Perhaps this impresses me because I can’t imagine running the Appalachian Trail twice a year, only at night, trying to avoid a man eating Bigfoot. If we all had to do that every year, it would quickly sort out the wheat from the chaff, if you know what I mean. And that means that the birds you hear at sunrise, the new voices that join the chorus each day, those aren’t just any birds, those are the survivors. So yes, winter was hard for us, I won’t deny it, but with each new warbler that arrives on a spring wind, take a moment to appreciate just how arduous and therefore amazing their journey to this season of plenty is. 

References:

Black and White Warblers: http://www.allaboutbirds.org/guide/Black-and-white_Warbler/id

Black Throated Green Warblers: http://www.allaboutbirds.org/guide/Black-throated_Green_Warbler/lifehistory

About Migration from the Cornell Lab of Ornithology http://www.birds.cornell.edu/AllAboutBirds/studying/migration/

From the Eastern Kentucky University, a marvelously in depth and referenced website about birds: http://people.eku.edu/ritchisong/avian_biology.htm

Migration altitude from Cornell: http://www.birds.cornell.edu/AllAboutBirds/studying/migration/pathways

                                                                               

Paleobrain and spring bird song

-->

Note: This program first aired May 9, 2015. 

Spring, such a sweet word here on the 44^th parallel. All winter long we ache for it, and then suddenly it’s here, and it is a revelation each and every year. And the revelations are for all of the senses. Visually things reappear as the snow pack melts, dog toys, garden tools, the tiny green shoots of the chives and the daffodils. When the air warms and moistens, smells return-rotting leaves, broken balsam branches, open water. Your skin knows it is spring by the warmth of the sun on your face, the softness of the humid air on your body, and the rare and joyful days when you can walk outside without a jacket. For me though, the sense that is most enlivened by the start of spring is the auditory one; as much as I love the warm air and sunlight, the increasingly complicated soundtrack of spring is the sign I love best.

Winter is a season of silence, punctuated by gusty wind, the breaking of snow laden branches and the twittering of the same familiar avian cast at the bird feeder: chickadees, nuthatches, juncos, gold finches, purple finches, redpolls, tit mice, blue jays, and downy and hairy woodpeckers. During the right kind of storm, if you are patient, you can hear the snowflakes hitting the ground. Go for a walk on a bright cold morning and the snow creaks under your boot steps. Sparse is winter’s soundscape.

Spring by contrast is an every growing cacophony. This winter was cold enough that our precipitation was all snow, and the sound of the spring’s first rainstorm on my metal roof was a delightful surprise. More so than weather, the sounds of animals coming back to life are what most of us think of as the sound track to spring. Chickadees may have been singing since January or February, but the woodcock is the first bird I hear that tells me that winter’s back has indeed been broken. Next comes the phoebes, and the wood frogs, then hermit thrushes, then the peepers. I heard a familiar whistle and looked up to see a broad winged hawk pass overhead. Soon sunrise will bring with it the restless tuning of a symphony of little warblers. Our current cold gray weather has slowed the progression of spring migration, but when the sun comes back out and the air starts warming in earnest, each day will bring a new voice to the outdoor audio mix.

As this happens, I would encourage you not to worry about identifying the bird you are hearing, at least, not at first. Just let your brain do what it does best, let it tune into the sounds around you out side. Like an old fashioned radio, you just need to spin the dial to the background bird frequency and your brain will do the rest. Suddenly without realizing you heard anything, an awareness will bubble up into your consciousness that you just heard something you don’t recognize, or do recognize but haven’t heard yet this season. Many a spring morning I have been draw into consciousness, pushed out of that light early morning sleep by that just below the conscious part of my brain, as it got excited by hearing a new bird song, and had to wake me up to share the excitement. We are evolved to do this, to pay close attention to the goings on in the world around us. All of our senses, dulled as they are by modern life, have hundreds of thousands of years of accumulated  evolutionary honing for just this purpose. A couple hundred years of being industrialized doesn’t make that go away.

There’s good genetic evidence for this too, scientists have shown that humans and birds use the same genes to fire up the same parts of their respective brains used in communication. I don’t know if birds’ brains are stimulated when I talk to them as I walk through the woods, but I am sure that my human brain responds to bird song, even when I am not consciously listening to birds, and it is a remarkable experience. So this spring let yourself just hear the birds, let your brain recognize and sort out the different songs, get familiar with the patterns and then you will notice when they change. This is the brain’s true work.

References:

Genetic evidence for birds and humans sharing communication genes: https://today.duke.edu/2014/12/vocalbird

Ok, but I still want to know WHAT birds I am hearing: http://birdcast.info/forecast/24-april-1-may-2015-forecast-and-thats-a-cold-shot-baby/#MidwestNortheast

If nothing else, listening to the birds will make you feel better: http://www.sciencedirect.com/science/article/pii/S0272494413000650

Blue Jays and Hunger

Note: This show first aired September 27, 2014.

 

I have red oaks around my house, which means this time of year, I have blue jays. I watched them the other day from my desk, looking out my window at the rain. They hopped and flapped from branch to branch at the top of the trees I see from my third story vista, searching for acorns, their preferred food this time of year. Hence the correlation: oaks and jays. Spending time beneath these branches is a bit of a risk, acorns frequently rain down, dropped accidentally. Jays hold the acorns in their claws and pound away at them with their thick beaks, cracking them open to access the nutritious nutmeat inside. This time of year, it’s likely to be all that they are eating.

There’s a reason we humans think about eating all the time. In the natural world, in the world we evolved in as animals (the animals we still are despite our computers and phones and refrigerators), what else is there to think about except finding food? Food is the constant vocation for wild animals, the number one job of all consumers is just that, to eat. Without enough food, there is nothing, no energy to run the metabolism that drives the fulfillment of genetic destiny. Food first, sex later.

I imagined what that would be like, to wake up in the morning like a wild animal, each and every morning of every day of your life thinking about food. Everyday a new day, a fresh opportunity to eat, or starve. Imagine getting out of bed in the morning in a house with no kitchen. No cupboard, no fridge, no food stores of any kind. Your day starts with you going outside to find something to eat. Every day starts that way. Reality TV aside, this is a marginal existence, an existence that honed us through natural selection oh so many years ago. An existence we pay no attention to now, unless you are a neo-aboriginal, experimenting with “rewilding light”, or desperately poor.

It turns out that Blue Jays, though they live the life of wild creatures everywhere, have a strategy for food scarcity, a strategy to cushion the pangs of hunger. They cache food, acorns and other mast crops from the forest. They can move hundreds of acorns a day, thousands a week, hundreds of thousands during a season. They bury them in small groups in the soil of the forest floor, and have a retrieval rate, according to one study, of about 30 %. That leaves about 70% for other animals to eat, or to germinate, dispersed so widely and nicely from the parent tree. Other studies show that Blue Jays are real foodies, picking only the healthiest and most viable acorns for caching, which means in practice, oak trees have come to depend on this noisy bird for dispersing their seeds. The idea is out there that Blue Jays are at least in part responsible for the rapid reforestation that occurred after the last of the glaciers left New England twelve thousand years ago. That’s a mighty job for a small blue bird. Americans are estimated to waste about 40% of the food we buy, and our food waste doesn’t feed other animals or grow forests, most of it rots in land fills (compost piles not withstanding). It’s a statement of how far out of the system we’ve come.

If I can’t think of the Blue Jays as facing each day with an empty belly (though in practice, even with food stored away, there are not guarentees), there are certainly other animals that wake up each morning with a clean slate. The coyotes I have been hearing around my house every night for the past two weeks don’t cache food. They spend all their time searching. What if I lived more like a coyote instead of a blue jay? What if every day that dawned was a brand new challenge to fill my stomach, as unconnected from the day before as to the day ahead. Each day an individual exercise in survival, life a series of these days strung together, one after the other, going on until I fail.

The blue jays I see this fall I watched fledge in July. Fledging day dawns with a ruckus coming from those same tree tops outside my 3^rd story window, the young hop and flutter from branch to branch all the while encouraged by the screeching calls of the adults. I imagine they are saying “come on come into this world, where your pursuits must be single minded, and your eyes clear”.

References:

Blue Jay basics from Cornell: http://www.allaboutbirds.org/guide/Blue_Jay/lifehistory

Birds of North America Online: http://bna.birds.cornell.edu/bna/species/469/articles/introduction?__hstc=75100365.3158294d7b302ccb4baa709ab0dcc6f9.1397130536637.1402758359782.1411606172833.6&__hssc=75100365.1.1411606172833&__hsfp=1771447269

Good citations to studies if you are a paid subscriber to the Birds of North America site

Nice article with a few more details about cache retrieval rates (presumably from the above studies) http://www.courierpress.com/lifestyle/blue-jays-cashing-in-on-caches-to-survive

Natural History piece from Loyola University: http://www.loyno.edu/lucec/natural-history-writings/blue-jay-acorn-planters

A Visit from the Grackles

Note: This program first aired on October 26, 2013.

Just last week, my neighborhood was taken over; from high up in the tree tops came a sound like the rusty hinged doors in a creepy haunted house, opening and closing over and over again. Interspersed with the creaking came squacks and knocks, it was a noisy crew of interlopers up there. The tops of the trees in my home territory were full, at least for a fleeting moment, of grackles.

Grackles are icterids, a family of songbirds that includes blackbirds, cowbirds, meadowlarks, bobolinks and orioles. They are an entirely new world group that encompasses about 100 different species between North and South America. The grackles in my woods were common grackles, Quiscalus quiscula, and if you look in the bird books you will find that there are several different races of this species, geographically distributed around the eastern half of North America, though they are making their way west as well. Grackles are birds of edges, they thrive in patchy habitat, open areas interspersed with wooded cover. Before European settlement they were not especially common, because much of North America was thickly wooded, too thickly wooded for grackles to proliferate. The subsequent development of the landscape here has been a boon for them, and their population has increased right alongside ours, as we clear more land for our homes and farms, and they respond in kind. In a sense, their population is tied to ours.

Which is interesting and a little ironic, because many people don’t like grackles all that much. Bird books describe them as boisterous and noisy and they are noted agricultural pests.  Online bird forums are loaded with irate posts from backyard bird watchers, all desperate for ways to keep grackles out of their feeders, as the grackles are thought to bully the other birds and prevent them from accessing food. While they are in the Passerine order, the song birds, grackles are not likely to sing you to sleep, their chorus sounds more like this: (play chorus from ebird). People like sweetly singing, little rare birds; common, loud, indistinct markings? Grackles have all the chips stacked against them.

That being said, I have nothing against grackles, and in fact, walking out into the yard and having my attention drawn to the cacophony in the trees was a magical moment. It was the end of a gray day, and suddenly there was new life in the air. These gatherings are their good byes, they are massing in preparation for leaving, or perhaps are already on their way, using my oak trees as a rest stop to eat acorns as they make their way south. And eat acorns they do. Have you ever tried to bite into an acorn? Its not easy, yet acorns are a favorite winter and migration prep food for grackles. They actually have a sharp keel in their mouth on their upper pallet that allows them to cut open the acorn. They are smart too, they are among the birds that practice “anting”, a behavior in which they land on the ground and allow ants to crawl up into their feathers. The presumed function of this behavior is to rid themselves of parasites. And they are beautiful. From a distance or in flat light they appear black, but when the sunlight hits them just right, their feathers reflect a gorgeous array of irridescent purples and greens.

So I was sad to see them go. One moment they were there and the next it was just silent empty trees. The briefness of their presence made it all the more special. Perhaps, had the whole flock taken up residence for the summer, I would have grown tired of the squeaks and scratches. But that isn’t what happened. Instead they were here just long enough to draw my attention, and then before I got a really good look, they left, leaving me wanting more. It is a reminder to not take anything in nature for granted, regardless of how common place it may seem to those around you. One person’s mundane is always another’s magic.

References:

From the Cornell Lab of Ornithology (the definitive online resource):
http://www.allaboutbirds.org/guide/Common_Grackle/id

Nice info from a local North Carolina Audubon chapter newsletter http://www.meckbirds.org/idbehavior/pdfs/grackles.pdf

Fledging Day

Note: This program first aired on June 29, 2013.

The other morning I got a phone call. It was my niece, saying, “Sarah, Sarah, I found a baby bird on the lawn! I watched it for twenty minutes and it is still there, can I keep it for a day?” I told her to leave it where it was, and that I would be right over. When I arrived we found not one but two baby chipping sparrows, staying quite still in the grass, minding their own business, and two adult chipping sparrows, noisily and nervously flitting about in the trees above. The date was June 14, what many Americans celebrate as Flag Day; for me now it will always be Fledging Day.

Merriam Webster defines fledge, the verb, as “to acquire the feathers necessary for flight or independent activity, also to leave the nest after acquiring such feathers”. The word can also be used as a transitive verb, which simply means it has an object, as in “to rear until ready for flight” or, my favorite, “to cover with or as if with feathers or down”. The definitions make me feel that it is as much about getting the feathers as it is about leaving the nest, which may be, because you can’t leave the nest until you have the feathers.

The little chipping sparrows we found were in fact fledglings, young birds who, under the care of their parents, having grown sufficient feathers, made the leap from the nest into the big world beyond. These sparrows, like most small song birds, are what is called altricial at hatching, meaning they are tiny, without feathers and with eyes closed. They can’t keep themselves warm, and are dependent on their parents for everything. They look like little fetuses, which is essentially what they are. They will live in the nest for days to weeks as they grow, for example, those chipping sparrows were in the nest for about 10 days before they fledged. The rate at which these babies develop is quite amazing, it seems like you could literally watch them grow. For altricial birds, fledging means growing enough feathers to leave the nest, not necessarily having the ability of full flight.

On the other end of the baby bird spectrum (and it is a spectrum) are birds who are precocial at birth, meaning they have feathers, open eyes and are capable of movement when they hatch, and may or may not feed them selves from the start. Ducks and other shore and water birds exemplify this pattern. The babies may not be able to fly immediately, but often they can swim.  For precocial birds, they have fledged when they can actually fly.

It is curious that there is such a difference in the stage of development of baby birds when they are born. This difference is a result of evolution. Nature has presented a problem to birds everywhere, namely “How do we keep our vulnerable young from getting eaten by some hungry predator?” (truly, the problem that faces all parents in the world). For birds, evolution has produced two quite elegant solutions, based on resource availability, and with pros and cons to each. Song birds migrate great distances to come to habitat with sufficient food resources and nesting areas. They have evolved to put their energy into simply getting here and getting down to the business of mating as soon as possible. Energetically that means that they put relatively little into their eggs, and the less you put into an egg, the less you are going to get out of it, hence the helpless altricial young. They are able to invest less bodily energy into egg production because once the young are born, they are able to collect plenty of food to feed them; the parents’ investment is on the outside of the egg shell. This is still a dangerous strategy, though, as finding a nest full of baby birds is like winning the lottery for a predator. It’s a concentrated source of nutrition, those tasty little niblets are all in one handy spot, the nest. Hence the speed with which these babies grow. Evolution has favored the fastest periods of in nest development, because the whole time they are in the nest, those baby birds are easy targets.

Precocial birds eliminate the possibility of having all of the young eaten in one predator attack, by dispersing them from the nest as soon as possible, mainly, as soon as they hatch. Individually they may be picked off, but they won’t all go together in a big gulp. The trade off for this in the physiological preparation of the parents. Their investment, particularly that of the mother, is on the front end of the nesting process; she must eat enough while developing the eggs to create a big fat juicy yolk laden egg. An egg like that contains enough nutrition to grow a baby bird that has feathers and run around as soon as it hatches. This strategy works really well, but obtaining that kind of nutrition on the front end is clearly not an option for many kinds of birds. The process of evolution has guided different bird species in different circumstances in different directions, and hatchling development is a perfect example of this. Happy Fledging Day everyone!

References:

Richard Sibly, et al, Energetics. Lifestyle and reproduction in birds PNAS, April 24, 2012  http://www.pnas.org/content/early/2012/05/17/1206512109.full.pdf

Mary Holland Naturally Curious 2010, Trafalgar Square Books—This fantastic book is also a popular blog and an email list serve: http://naturallycuriouswithmaryholland.wordpress.com/

Paul Ehrlich et al, The Birder’s Handbook: A field guide to the natural history of north American birds, 1988, Simon and Schuster. A classic, with detailed species accounts and a wide array of content essays.

One of the most comprehensive bird websites out there, from the Ornithology Lab at Cornell University http://www.birds.cornell.edu

The information about the evolutionary strategies of precocial vs. altricial young came from the Stanford University bird website: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html They seem to have an active on campus birding community.

A Robin's Life Work

Note: This program first aired June 22, 2013.

I’ve had the pleasure of watching a pair of robins nesting this spring. For the past several years, they have taken to nesting on human made structures around an outbuilding at my house; on window ledges, on top of propped up ladders, on exposed beams. I’ve watched them in the past, but I’m ashamed to say that I didn’t really pay attention to them, due to a mix of caution and frank snobbery. Part of me didn’t want to disturb them, and part of me thought “oh, well, they are just robins. Robins are everywhere, they are so common, there’s nothing special about them.” This is a trap that naturalists everywhere fall into, we want to spot the rare bird, be the first to find the unusual flower, identify the large mammal tracks. So caught up are we with the excitement of the uncommon that we become blind to the more ordinary friends we see around us on a daily basis; the dandelion, the daisy, the sparrow, the robin.

This year I let go of my pretension. I was in a class, and one of our assignments was to watch a bird for an hour and record our observations. Because I am both an over achiever and an over scheduler, I needed to find an easy bird to observe, something close to home, something predictable, something like a robin nesting on a window ledge right out my front door. I decided that an hour was clearly not long enough, I would watch them during their entire nesting cycle, and document what I saw (that’s the over achieving part). What I learned is that every creature, every organism, every entity out there has something to teach us, if we are willing and open to learn it.

Several weeks ago, the robins began building their nest; The female builds the nest, with help from her mate. I didn’t know that from watching, a little back ground reading never hurt anyone. The pair struggled to construct the nest out of dry grass during high winds. It seemed futile to me. Then it rained, the ground became wet, mud formed. Robins construct a substantial part of their nests from mud, and these robins didn’t make any progress on their nest building until spring weather favored them with some building material. Suddenly, from what looked like a sloppy pile of mud on a window sill, a beautiful grass lined nest was formed. Next the female seemed to be testing out the nest, sitting in it some times leaving it other times. I realized she was preparing to lay eggs. One day I saw an egg in the nest, and worried that she had abandoned it, as she was not there every time I looked. Again, just as suddenly there were four eggs in the nest, and she was sitting consistently. Robins, like many birds will delay the incubation until all the eggs in her clutch are laid, so they all hatch at the same time. Her spotty attendance to the nest was what I was observing, by not sitting on the eggs she was keeping them cool so they wouldn’t start to develop.

The book said that the eggs would hatch in 12 to 14 days, so I marked the range of due dates on my calendar. The first due  day two eggs had hatched, the second day a third egg had hatched, and by the third day all four had hatched. That meant that the first two had a two day head start on the last hatchling, and I wondered how that would play out in nest dynamics. The book also said that they would fledge in 14 to 16 days, meaning they would grow from helpless pink featherless grubs to fully feathered birds in about two weeks. I couldn’t believe that, so I decided to photo document their growth, with a single picture each day. It turns out that a photo really is worth a thousand words. By day 12 the largest nestling had fledged. By day 13 the next one had. Today is day 14. I fully expect that by the end of today when I go out and look, the nest will be empty.

In watching these animals, who I am so grateful to for accommodating my curiosity, I was given a gift. I saw how fast those babies grew, and thought of all of my friends and their children, and my young niece and nephew. I watched the mother sit faithfully on the nest for two weeks, and then saw the father return to share feeding responsibilities with the mother once the eggs had hatched. I was aware of the parents’ alarm when I would approach the nest for my lightening fast once daily photo, observing how the young would immediately lower themselves in the nest in response to their parents’ calls. When darkness fell each night, I would imagine the mother robin, sitting on her nest in the dark, with only her self between her babies and the unknown and hungry night beyond. Raising those babies is truly a robin’s life work. What kind of person am I if I am not awed by that?

As we enter this period of summer’s bounty and ease, pick something, anything, anything you will see on a daily basis, don’t wait for the Blackburnian warbler or the rose pogonia. Watch it until it brings you to your knees. I promise you, your life will be richer for it.

References:

The Birder’s Handbook Paul Ehrlich et al, 1988 Simon and Schuster, the Bible for concise  go to info about North American bird natural history.

Nice little website about robins, including opportunities for citizen science. http://www.learner.org/jnorth/tm/robin/EggstraEggstra.html

Don't Call It a Comeback: Wild Turkeys in New England

Note: This program first aired on November 24, 2012.

Come November, many minds in America start daydreaming about the bird that could have been our national symbol, the Turkey. Amazingly, that bird you buy in the grocery store or order from your local farm is the same species as those wonderful prehistoric baby dinosaurs you see in flocks along the roadside or in the fields as you drive to work.

Wild turkeys are found throughout the lower 48 states and into parts of Mexico. The species is actually comprised of 6 sub species, separated by geography. All of the sub species are derived from the southern Mexican wild turkey (Meleagris gallopavo gallopavo). This is the species that the Aztecs of Mesomerica and the Anasazi of the desert southwest were known to have domesticated, one of the few “New World” organisms that lent itself to agriculture. Interestingly, this Aztec domesticated turkey was then brought to Europe by Spanish conquistodors and gained popularity there.  It was further selectively bred in Europe and then came back to the new world with the colonists, who had no idea that there was already a wild turkey waiting for them here in colonial North America.  The sub species we see here in Maine is the Eastern Wild Turkey; Meleagris gallopavo silvestris), and as a sub species it is able to interbreed with the domesticated turkey.

Wild Turkeys were once abundant throughout New England, but the spread of agriculture during the colonial period up through its peak in the 1800’s, combined with unrestricted hunting nearly exterminated the species in our area. Most New England states went from being almost entirely forested at the time of European colonization to being 60 to 90 % cleared for cropland and pasture. This clearing of the land strongly decreased diversity across the landscape and obliterated wild turkey habitat. Turkeys need mixed woodland with nut bearing trees like oaks and beeches as a food source. They roost high in trees at night to avoid nocturnal predators. Young turkeys need dense shrubbery for cover and lots of insects to feed on to fuel their rapid growth. A patch work of diverse northern hardword forest is ideal for them, and that is what has been regenerating in much of New England since agricultural clearing peaked in the 19th century.

The turkeys we see around today are a result of reintroduction programs throughout the northeast.  Maine’s reintroduction program started in 1977 and 78, with 41 turkeys from a wild population in Vermont, followed by 70 more Connecticut turkeys in 1987. From those 111 birds come the 50 to 60,000 we have in the state today. That is a phenomenal recovery, and speaks clearly to the importance of habitat restoration in the field of conservation biology. When released from the pressure of unregulated hunting and total habitat destruction, wild turkeys are able to thrive, achieving population numbers and ranges that are likely higher and wider than the precolonial population. So if you are partaking in the traditional turkey feast some time this holiday season, take a moment to reflect on the marvelous resilience of the bird you are eating.

References:

Maine Inland Fisheries and Wildlife info:
http://www.maine.gov/ifw/wildlife/species/wild_turkey/index.htm

Vermont also has some nice things to say about wild turkeys: http://www.vtfishandwildlife.com/turkey_facts.cfm

The Lewiston Sun Journal article on wild turkeys in Maine: http://www.wired.com/wiredscience/2010/02/lost-turkeys/

Yep, he really did say that: http://www.loc.gov/exhibits/treasures/franklin-newrepublic.html#29 Ben Franklin, though he never made a public fuss about it, did think the turkey to be a more respectable bird than the eagle.

Nice article in Wired magazine, regarding new research on the domestication of turkeys in North and Meso America http://www.wired.com/wiredscience/2010/02/lost-turkeys/

Jared Diamond Guns, Germs and Steel—learn all about the few species that native North Americans were able to domesticate (and why that bad luck doomed them).