Saturday, January 14, 2017
Note: This program first aired on January 14, 2017.
We’ve been talking lately about the fact that water is life. It plays a critical role in our most fundamental biological processes, without it life could not go on. We’re told to drink water, maybe as much as 8 cups a day, in order to have enough liquid on board to meet our needs. Plants use liquid water too, but water vapor, the gaseous form of water is ultimately what drives water movement from one part of a plant to another. Ice, water in its solid crystalline form, is generally a liability to life. Ice forming in and around cells in living tissue can result in mortal damage to those cells. So yes, water is life, but the ways that water associates with life vary widely.
If you keep house plants or grow a garden, you know that plants need water. Water is an ingredient in the fundamental biological processes of photosynthesis and respiration, both of which plants partake in. When we think of plants that live in severely water deprived environments, our minds go first to the desert. Though there is little water in the desert environment, there are plants adapted to take advantage and maximize the little water that is there. Those adaptations encompass mechanisms to store water when it becomes available, reduction of the normal water loss that results from metabolic function, and enhanced ability to photosynthesize in high heat. We all know what those plants look like—fleshy, spine covered, leafless cacti. Plants adapted to survive with just barely enough water.
There is another kind of water limiting environment out there, it’s called winter. In winter, water is typically locked up in solid form, unavailable for biological processes. Additionally, the cold air of winter can hold less water vapor, so there is less gaseous water around as well. The plants we see all around us here in the temperate zone reflect a variety of ways to deal with this seasonal water stress, to deal with the fact that water is life, but part of the year they can’t access it.
Plants deal with the inability to get water in winter in many ways. Some just avoid the issue altogether, over wintering as a seed (in the case of annual plants), or underground roots or bulbs. These strategies enable the plant to lie dormant, and suffer no water loss during the time when liquid water is scarce. Others, the deciduous woody plants, shed their leaves, and for good reason. Leaves are the site of water loss in leafy vascular plants. Water moves up through the plant from roots, which gather water from the soil, to the leaves, where water is used in photosynthesis. It isn’t pumped, but rather is pulled. As leave release water vapor, through pores on the underside of leaves called stomata, it creates a vapor pressure gradient. Water exits the leaves, creating a water void that must be filled, and is filled, with water rising through the plant vascular tissue, called xylem to replenish the water lost by the leaves. In the winter, water can’t be gathered by the roots, as the soil moisture is frozen solid, so water can’t move up the plant to replenish the leaves. Additionally, much of the vascular tissue of the plant is frozen, compounding the barrier to water transport. If the plant had broad leaves that continued to lose water vapor through stomata all winter long, there would be no source of water to replenish the leaves. Desiccation would result, and cell death. The shedding of leaves by deciduous trees is a direct response to this water stress. By shutting down all transpiration, deciduous plants reduce winter water loss to a minimum. Trees that don’t lose their leaves in the winter, primarily the conifers in this part of the world, have other ways of minimizing water loss in the winter. The needles of these trees are in fact leaves, but they do not photosynthesize year round. In the heart of winter, the stomata of these leaves are closed shut, and water loss through transpiration drops to a minimum. In addition, the needles are encased in a thick waxy cuticle that is not very permeable to water, another adaptation to minimize water loss that could occur through diffusion of water vapor through a permeable leaf surface.
Water is life, but in winter, even though we often have a lot of precipitation, it is in short supply. Plants show a remarkable diversity of adaptive strategies to deal with this seasonal water stress. We could learn a lot from them.
Peter Marchand’s Life in the Cold: An introduction to winter ecology is a classic in the field. (University of New England Press)
Saturday, December 31, 2016
Note: This program first aired on December 31, 2016.
There has been a lot of talk lately about the fact that water is life. We spoke last week about the biochemical reality of that concept, and looked at how water is involved in photosynthesis on a molecular level. Water is key to the reaction that allows plants to transform the energy of the sun from non storable electromagnetic radiation to storable chemical energy. The other great biochemical reaction that life depends on is respiration, the liberation of energy from chemical bonds. And once again, as in photosynthesis, water isn’t the main focus of the chemical reaction, but an extremely useful and in fact necessary bystander, without which the reaction could not occur. The star of the respiration show, the final product that is the real reason for the reaction to occur is called ATP (or adenosine triphosphate), a high energy, unstable molecule that does a good job of temporarily holding on to the chemical energy liberated from the glucose molecule, for a matter of seconds to minutes. Everything that happens in respiration supports the formation of ATP, one way or another.
Typically we think of the respiration reaction as combining glucose and oxygen gas to yield carbon dioxide and water. In reality, we combine glucose, oxygen gas and water to yield carbon dioxide and even more water. We put some water in on the reactant side, and get even more water out on the product side.
Respiration, particularly the aerobic or oxygen using kind we are talking about today, is, just like photosynthesis, a fabulously complicated process with many mind numbing intermediate molecules. The first part of the process, glycolysis, has 10 sub reactions all of its own, just to turn a 6 carbon glucose molecule into two 3 carbon molecules. Those three carbon molecules, get further processed into two 2 carbon molecules, and then enter something you may remember from school, the Citric Acid cycle, or Kreb’s cycle, which uses a series of organic acids to further process the two carbon molecules to their ultimate fate, being turned into carbon dioxide gas. And all along the way, at key steps, electrons are getting moved around, electrons that started in the glucose molecule. Electrons that originally came from water molecules back in the photosynthesis reaction that formed the glucose.
If you are thinking ahead, you can see where this is going. Water plays several roles in respiration. The first is that it is the solvent in which all of these other chemicals are dissolved. Without water, these reactions would have no matrix within which to take place. Secondly, water plays a supporting chemical role in the citric acid cycle, stepping in as a reactant. Water also allows for the initiation of respiration by hydrolyzing or breaking down starch and other more complex carbohydrates into individual glucose molecules. Thirdly, and probably most importantly, water gets formed as a result of all of those electrons getting passed around.
As the electrons get moved from one intermediate carrier molecule to another, conditions inside the cell get set up for the generation of ATP, which remember is the ultimate goal of respiration. Once the stage is set for the ATP generation, virtually all of the useful energy has been wrung from the electrons, and the last hand off, to what we call the terminal electron acceptor, releases the last of the energy. The terminal electron acceptor is oxygen (that is why you need to breathe air with oxygen in it). Oxygen on its own though, with an extra couple of electrons, is what we call a free radical, an unstable and potentially destructive molecule. The destructive power is based on the imbalance of the electrostatic forces in the atom. To counter this, the oxygen quickly joins some hydrogen ions that are available in the cell, and forms water, and the products of respiration are complete. If water wasn’t formed as a result of respiration, we would be left with a free radical form of oxygen which can be destructive to the cell. So once again, the Oscar for best supporting chemical in a biological reaction goes to: water.
As if often the case, any college level Biology text book should cover this in sufficient detail. I use Freeman et al, Biological Science 6th ed. Pearson Higher Ed
Interesting table of free radical https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/table/T1/
From this article in Pharmacology Review: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/
Saturday, December 24, 2016
Note: This program first aired December 24, 2016.
There has been a lot of talk lately about the fact that water is life. That means a great many things to a great many people. To the fishing communities here on the coast of Maine, water provides a living, a work place, a source of income and food. On a hot summer day water provides relief, a place to cool your body. For many people the water is life idea is a spiritual endeavor; water represents the blood of the earth, traveling across the body of the earth, bringing sustenance. Even those recreationalists less spiritually aligned recognize water as a means of direct immersive contact with the natural world. We all understand intuitively that water is life, but few of us understand exactly why. But talk to a biologist, or a chemist, and you will learn that “water is life” has literal concrete molecular meaning.
Water has a specific and intimate role in the most basic biological reactions, playing a key part in both photosynthesis and aerobic respiration. I’ve talked about photosynthesis before on the show, but it is hard to overemphasize the importance of this reaction to the fact that we are all here. It is the means by which all of the energy our bodies use becomes accessible to us; our bodies can’t use light energy, but we can use the chemical energy stored in organic molecules created by plants and transferred up the food web. Virtually our entire economy is based on photosynthesis*, and until a couple of hundred years ago that was all “current photosynthesis”. The advent of the industrial age brought a reliance on fossil fuels, but the “fossil” in fossil fuels is photosynthesis. All the chemical energy stored in oil, gas and coal originated exactly the same way as the energy in your bowl of Wheaties-through an intricate set of biological reactions that move electrons up and down and from atom to atom and result in a final product that has higher potential energy than the original ingredients. Photosynthesis pushes energy up hill. We rely on it utterly. And it relies on water.
The kind of photosynthesis we are talking about, oxygenic photosynthesis is the kind you learned about in school, when you learned that plants can take carbon dioxide and water in the presence of sunlight and make glucose and oxygen. A specific group of bacteria, called cyanobacteria (also known as blue green algae, but this is a misnomer as they are not algae) and certain members of the eukaryotes, a group of organisms that includes us and pretty much everything else you would picture as alive are the organisms that can perform oxygenic photosynthesis. There are other forms of photosynthesis, but they don’t make oxygen, and more importantly for the story today, they don’t use water.
So what role does water play in this most fundamental biological process? There are actually two key roles, Water goes into the photosynthetic reaction and gets deconstructed for parts. The oxygen gas generated as a byproduct of this reaction, the oxygen that changed the composition of the atmosphere and enabled all of the life we see around us is the O in H2O. Take apart a couple of water molecules and you have two oxygen atoms, that bond to each other to create the diatomic oxygen gas we know, love and depend on. But photosynthesis isn’t trying to create oxygen, it is trying to turn electromagnetic energy into storable chemical energy, and to do that it needs some electrons. Electrons are the currency of non nuclear atomic energetics. The light energy that gets absorbed by chlorophyll serves to excite electrons, and the net result of the first part of photosynthesis is that a special chlorophyll molecule called the reaction center loses some of these excited electrons as they are passed on to other molecules in the photosystem. That is its job, to absorb sunlight and pass that energy along to the rest of the system in the form of electrons. To keep doing its job though, the reaction center chlorophyll needs electrons to replace the ones it gave away. Where does it get those replacement parts? You know it already—it gets them from water. That is the reason water is required for photosynthesis, and therefore life—its electrons.
Getting electrons from water isn’t easy to do. Oxygen is an incredibly greedy atom and is loath to relinquish any electrons, chemists call that being strongly electronegative. The only things that can get electrons away from a water molecule are an even more strongly electronegative reaction center chlorophyll molecule, and some very clever enzymes.
So there you have it, water is life, because water is the source of the electrons that provide the medium by which the sun’s energy gets turned into chemical energy, and as a handy byproduct also happens to provide the world with the oxygen it needs. What we need that oxygen, and yet more water for, we’ll talk about next week.
As if often the case, any college level Biology text book should cover this in sufficient detail. I use Freeman et al, Biological Science 6th ed. Pearson Higher Ed
Saturday, December 3, 2016
Note: This program first aired on December 3, 2016.
If you wanted to design an ocean animal that is perfectly constructed to get hit by ships, what characteristics would you include? It should probably be big, and slow moving. Make it dark so it is hard to see. If it is a mammal, it will need to spend time at the surface, so it can breath. It should have to spend long amounts of time feeding on very small food items, again, often at the surface, at night. Make it easily stressed by noise, which decreases its ability to communicate with others of its kind. Put its range right near shore, in major shipping lanes near highly populated areas.
This isn’t just a hypothetical exercise, this animal actually exists. It is called the Eubalaena glacialis, North Atlantic Right Whale, and it is one of the most endangered large whales in the world.
Many people have heard the story of the Right Whale, so called because they were the “right” whale to hunt especially in the early days of whaling. As a species evolved to feed in relatively shallow productive water of the continental shelf, they stay close to shore, which made them accessible to land based hunters in small boats. They could be brought to shore and processed on land, and were an important part of the land based whaling industry, before the more ocean going sperm whale was discovered and chased all over the global ocean on multi year whaling expeditions. Right whales also have enough blubber, or body fat, to lower their overall density enough that they will float when killed, again, making them easier to manage from a small boat. It is hard to know how many Right Whales were around before commercial whaling began, but they received internationally recognized protection starting in 1935, after having been harvested consistently in the northwest Atlantic since the 1500’s, and most likely earlier in European waters. Researchers estimate that there were less than 100 North Atlantic Right whales left in the western Atlantic in 1935. Since that time the population has rebounded, but very very slowly. The most current published population estimate puts the number around 476 individuals, based on direct observation. Though they are no longer hunted, they are still highly endangered.
Why are they still endangered? If we return to our list of characteristics of our vulnerable ocean animal, we can start to see why. They like to hang out where we spend most of our time in the ocean too. They fish where we fish. They travel where we travel. The two big reasons that Right whales die as a result of human activity are 1. They get tangled in fishing gear and 2. They get struck by ships.
The fishing gear entanglement issue is complicated, and unfortunately seems to be a fact of life for North Atlantic Right Whales. Researchers have observed that 83% of these whales have scarring consistent with entanglement, and around half show signs of multiple entanglements. Changes to fishing gear are a start at preventing this problem, but there is further work to do.
On the ship strike side, and because I work at a maritime college I focus more on this end of things, some very positive strides have been taken. In areas where these whales are known to congregate at certain times of the year, speed limits have been imposed for vessels over 65 feet. These zones are called seasonal management areas or SMAs and came into effect in 2008. Compliance on the part of industry has slowly but surely increased since that time. Speed makes a huge difference. If a whale is struck by a ship traveling at 20 knots, mortality is 100%. When ship speed is reduced to 9 knots, mortality is around 20%. And it has had an impact. Before 2008, 87% of the ship strike mortality occurred within or just outside the SMAs, because that is where most of the whales were. Since these slow zones were established, all of the documented ship strike mortality events, averaging 1 per year, occurred outside of the SMAs. So just getting ships to slow down where the concentration of whales is highest has worked to decrease our impact on this population. Not that we should stop and pat ourselves on the back, there is certainly more to do. These whales continue to face the threats of ship strike outside of the SMAs, entanglement in fishing gear, increased stress from noise pollution, and the likelihood of a genetic bottle neck stemming from such low population numbers in the early 20th century. We’ll learn more about what is being done on a future show.
There is a ton of info out there on these whales, including many federal websites, due to the federal regulations stemming from the protections encumbered by the Endangered Species Act.
The study that documented the positive impact of the speed reduction zones: http://www.int-res.com/articles/esr_oa/n023p133.pdf
From the federal government: http://www.nefsc.noaa.gov/publications/tm/tm219/8_NARW.pdf
Saturday, November 19, 2016
Note: This program first aired November 19, 2016.
I know many of you listen to this show because you like hearing about the natural world, learning things you didn’t know before, and getting insights into the amazing mysteries of nature. I know this show, and this radio station as a whole can serve as a respite from the 24 hour news cycle, the information overload and the go go go culture we are awash in, even here in eastern Maine. And I know that after the last two weeks we’ve had, I should be offering you a show about kittens and puppies, just to provide something distracting, hopeful, sweet and kind.
I think you know what is coming. I can’t do that. Not yet anyway. I’m in the camp with the majority of those casting votes in the last election who are not happy with the results of the election. There are so many reasons, but one especially relevant to this show is the appointment of Myron Ebel to lead the Trump administration’s transition at the Environmental Protection Agency, an appointment that many presume will lead to Ebel’s nomination to lead that agency after the transition of power.
Ebel is a known and vocal climate skeptic who directs policy on energy and the environment at the Competitive Enterprise Institute, a think tank that both the New York Times and the National Review characterize as libertarian. While he says that he believes human caused climate change is real, he follows that up with the belief that it isn’t really a big deal, and certainly not something we need to worry about or more importantly, spend any money on right now. The main targets of his derision are the models and forecasts developed and constantly honed by climate scientists, in an attempt to predict the near climate future. And I quote:
*“… the scientific consensus is not based on known scientific facts. It is based on discredited climate model projections, such as the ones promoted by Gavin Schmidt at NASA’s Goddard Institute for Space Studies, and fantasy reconstructions of past climate history, such as the infamous hockey stick.”*
Climate models to have a degree of uncertainty, and scientists work tirelessly to revise the models, using “back casting” as a way to test them (can they run and accurately predict the climate trends we have already experienced? If so, than then you can have a relatively high degree of confidence in the model, within the strict limits of what it is designed to test). The International Panel on Climate Change reports take great pains to report confidence intervals with each of their predictions and prioritizations of climate related problems. So while Ebel seems to delight in denigrating what he calls unfounded climate alarmists, many of the forecasts he is critical of are coming with acknowledgements of the uncertainty.
Ebel’s think tank’s most recent policy position promotes anti regulation legislation, and that seems to be at the heart of this issue. Lowering the regulatory threshold is one of the main pillars of the Ebel’s career, and with climate change, the easiest way to do that is to deny the problem that the regulations are supposed to be addressing. If climate change isn’t really a problem, of course there is no need for the Clean Power Act, or the Paris Climate Treaty. It seems that the answer to when was America Great in the first place is the time before industry faced any kind of regulation. Annoying regulations like the Clean Air Act, and the Clean Water Act.
So for all the reasons to be concerned about the ramifications of the recent election, and there are many, incredibly serious ramifications, this one might be the most important. Climate change doesn’t just screw it up for us in America, it screws it up for everyone on this planet.
Administrator of the Environmental Protection Agency isn’t technically a cabinet level position, but it is high enough in the ranks to require Senate approval. We’ll get back to the trees and fungus and forests, plankton and algae and whales, the plants that run our lives, the winds that bring the weather and yes the kittens and puppies make us smile in the coming weeks. But in the mean time, call your senators. Tell them how you feel about someone who doesn’t take climate change seriously leading the agency tasked with protecting the environment we all share and depend on.
Senator Angus King: Augusta Office: 207 622 8292, Scarborough office: 207 883 1588 https://www.king.senate.gov/contact
Senator Susan Collins: Augusta Office: 207 622 8414, Bangor office: 207 945 0417 https://www.collins.senate.gov/contact
The New York Times profile of Ebel: http://www.nytimes.com/2016/11/12/science/myron-ebell-trump-epa.html?_r=0
The Competitive Enterprise Institute, where Ebel is Director of the energy and the environment policy division https://cei.org/
The Cooler Heads Coalition, a group of climate skeptics and deniers Ebel leads http://www.globalwarming.org/about/
*Source of the quote from the show: Myron Ebel’s blog post about a New York Times article attacking the climate scientist Willie Soon: http://www.globalwarming.org/2015/02/27/new-york-times-repeats-scurrilous-greenpeace-attack-on-willie-soon-without-checking-the-facts/#more-23224
The Clean Power Plan https://www.epa.gov/cleanpowerplan/clean-power-plan-existing-power-plants
Where he said that he thinks anthropogenic climate change is real, but that its not a big deal: http://web.archive.org/web/20161111000552/http://www.eenews.net/stories/1060041292
Really, here it is: http://www.nasa.gov/feature/goddard/2016/climate-trends-continue-to-break-records/
Saturday, November 5, 2016
Note: This program first aired November 5, 2016.
Food anchors us to the land(*), it places us in a landscape and timescape. Food also anchors us in our community. We share a common language with those who eat the same things we do, and food gives us a currency with which to exchange culture with people with different traditions.
I never feel more human than I do when I am eating wild foods. Whether it is incorporating a daily morning berry foraging walk that provides my summer breakfast, harvesting and tincturing a medicinal herb to support a loved one’s health, stumbling on an edible fungus in the fall or collecting favorite algae at the sea shore, nourishing myself from uncultivated yet bountiful sources feeds something as old as time in me.
I don’t as of yet hunt animals, so the wild food gathering I undertake is primarily focused on plants. With this in mind I signed up for a class with Arthur Haines, a well respected botanist here in New England and passionate and generous advocate for the wild food and rewilding movement. Our topic was acorns, how to collect, preserve, process and enjoy this at times prolific nut.
I was delighted to hear Arthur sing the praises of the Northern Red Oak acorn (Quercus rubra), a member of the Black Oak subfamily that includes Scarlet Oak, Pin Oak and many others. I live in a Red Oak forest, the acorns literally drop onto my door step in the fall. Northern Red Oak acorns are distinguished by their nutritional profile, they are nearly 50% lipid (or fat). Crack open a fresh Red Oak acorn and you will feel the oiliness on your fingers. That fat is mainly oleic acid, the same monounsaturated fatty acid that is found in olive oil. The rest of the bulk of the nut is complex carbohydrate, and a small percentage of protein.
The process of using acorns for food begins with gathering and sorting. It turns out not all acorns are created equal. Some are damaged right from the start, fail to develop to full size and are shed by the tree early. Others look like regular acorns, but when hefted in the hand reveal a lighter than average weight. They weigh less because they are hollow, or are in the process of becoming hollow. They are hollow because they are being eaten from the inside out by the larva of the acorn weevil, a small beetle that lays its eggs in the developing acorn. As the acorn approaches maturity, the egg hatches and the tiny larva, now housed inside its own food source, begins to eat. As it eats, it also respires, and just like we exhale carbon dioxide and water, so does the larva. That gas has mass and dissipates through the acorn shell, so as the larva eats the acorn, the acorn gets lighter and lighter. Once the larva has eaten all of the goodness inside, it exits the acorn through a little hole it creates---thus any acorn you find with a tiny circular hole in the side is no good—it is just full of acorn frass. Any acorn you find without the tell tale exit hole, that feels feather light, much lighter than all the others in your hand-if you cracked that one open it is likely you would find a number of acorn weevil larvae still munching away inside.
We can’t just shell an acorn and pop it into our mouths, and this is something aboriginal populations world wide figured out thousands of years ago. Acorns contain tannins, a group of chemicals that yield both a bitter taste and an astringent feel in the mouth. Primarily thought of as a defensive compound for the plant, some tannins have anti nutrient properties, while others (like the ones in tea) have strong nutritionally beneficial anti oxidant properties. The tannins in acorns are of the former variety, and make them in their unprocessed state, an unpleasant eating experience.
The processing may be one reason these native nuts have fallen out of favor, after drying, cracking and shelling, you still have to chop or grind them and then leach out the tannins. The process, though not intensive throughout, takes weeks. The result at the end though is a relatively bland flour, with a high healthy lipid content, and a very low glycemic index, suitable to mixing in with other flours in baked goods, or eating as a hot cereal with maple syrup. If you like getting connected with your food source, aren’t afraid a little work and are up for a culinary adventure, this would be a good year to try eating acorns. For many of us in eastern Maine, they are falling on our doorsteps.
On acorn weevils from Iowa State Extension service: http://www.extension.iastate.edu/news/2007/sep/072107.htm
Encouragement from the Earth Island Journal for eating acorns at Thanksgiving: http://www.earthisland.org/journal/index.php/elist/eListRead/this_thanksgiving_consider_cooking_with_acorn_flour/
Delta Institute of Natural History (and website of Arthur Haines, the botanist and wild food advocate mentioned in the program): http://www.arthurhaines.com/ *The first line of this show (about food anchoring us to the land, comes from Arthur’s description of the acorn workshop)
There are lots of references online for how to process acorns, some using hot water to leach the tannins, others using cold. Some crack the nuts immediately, others dry the acorns first (they are A LOT easier to shell if dry, and can be stored dry in the shell for years). The work shop I attended emphasized making the process efficient, but regardless—go ahead and experiment! There’s lots of info out there to get you started!
Saturday, October 22, 2016
Note: This program first aired on October 22, 2016.
Earlier this fall, a listener contacted me suggesting a topic for the show. He had just replaced his glass hummingbird feeder with a polycarbonate plastic one, in a successful attempt to thwart the yellow jackets that were frequenting the feeder. He wondered though, about the possible contaminants, especially BPA, that the birds might be exposed to. Anticipating the arrival of the ruby throated humming birds in the spring and watching them feed in our yards all summer long rank high among summer pleasures for many Mainers. But with growing awareness that problematic plastic additives show up anywhere, and everywhere, it has been only a matter of time until some one put two and two together and asked this question.
Plastics are polymers, chains of individual units (monomers) strung together chemically. Most plastics are a mix of different kinds of hydrocarbons, with various additives to give them specific physical attributes. These additives have various levels of fidelity to the plastic they are part of, and some readily leach out of the plastic into the environment. Awareness has grown in the past 10 years of this potential problem with the consumer goods and food packaging we contact on a daily basis.
Some chemical additives may be inert, other are quite biologically active and that is the crux of the problem. Bisphenol A, or BPA, the additive my listener asked about, is used in polycarbonate plastic, the kind that lexan water bottles, protective eye wear and DVDs are made of. It has proven itself to be, as many plastic additives are, a potent estrogen mimic, meaning, it binds to the same receptive sites in cells that naturally occurring endogenous estrogen does.
Estrogen is the female sex hormone in all vertebrates, from fish to mammals. It plays the same role throughout the vertebrate group, in carefully timed pulses it guides the development of the reproductive system. The biological or anatomical sex of an individual is the result of the relative balance of estrogen and male sex hormones like testosterone, and the timing of the exposure of cells to these hormones. Through the study of developmental biology, we’ve learned that the critical period for this exposure is very early in embryonic development.
Having an environmental estrogen out there can mess up this system, throwing off the balance of hormones, and the timing of exposure. And that is where most of the permanent impact of chemicals like BPA lies, by mimicking estrogen and flooding estrogen receptors in the cells of vertebrate embryos BPA can interfere with the normal development of the reproductive system of exposed organisms, be they fat head minnows, Japanese quail, or human beings.
Most of the research on the impacts BPA on wildlife has been on freshwater aquatic vertebrates, as it is easy for BPA to get into surface water through municipal water treatment facilities and industrial run off. The research on birds is much more limited, but that which is out there points to embryonic exposure leading to persistent malformations of oviducts and the shell gland (leading to thin and weak shells) in female birds, and changes to brain development in male birds leading to reduced copulatory behavior. These are problems, that, while initiated when the birds were embryos, don’t show up until they reach sexual maturity.
All of this bird research has been on model organisms like Japanese quail or domestic chickens, using exposure vectors like injecting BPA directly into eggs, or dipping eggs in an aqueous solution containing BPA. No one has looked at BPA’s effect on wild birds like humming birds, exposed through the parent’s ingestion of BPA laden sugar water from your new plastic hummingbird feeder. All we can say is that there is a demonstrated estrogenic effect in some birds in experimental conditions, but that the impacts on wild populations with more natural exposure are unknown. If there were negative effects to hummingbirds, I would expect them to be reproductive.
And before you all start writing me telling me that you can get BPA free polycarbonate and other plastics, yes, you can. It turns out that many of the chemicals used to replace BPA are simply other bisphenol chemicals, or are less well studied, and when they are investigated, turn out to have similar biological actions. So just because it says BPA free, doesn’t mean it is necessarily great.
If you are worried about the reproductive health of the hummingbirds who visit your yard, you may want to continue your search for the perfect glass feeder, or better yet, cultivate the original hummingbird feeder, a yard full of flowers.
Excellent review article in Dose Response, focusing on aquatic vertebrates https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4674185/
Full text of a Swedish PHd dissertation from the University of Uppsala on environmental endocrine disruption in birds: https://uu.diva-portal.org/smash/get/diva2:165990/FULLTEXT01.pdf
Environmental Defense Fund on BPA free: https://www.edf.org/health/three-reasons-bpa-free-wont-protect-you?utm_source=ggad&utm_medium=cpc&utm_campaign=gr-bpafree&gclid=COXaxd316c8CFQkkhgodBkkBtg
Other sources on BPA alternatives: http://www.the-scientist.com/?articles.view/articleNo/45789/title/Effects-of-BPA-Substitutes/
And from UCLA http://newsroom.ucla.edu/releases/chemical-used-to-replace-bpa-in-plastic-accelerates-embryonic-development-disrupts-reproductive-system