Thursday, May 31, 2012

Paleontological Flow ~ A Family in Mourning

I am fascinated by families that hunt fossils together.  The stories I’ve collected of such families, whose members understood fossils as remnants of ancient animal and plant life, go back roughly two centuries.  There isn’t something magical about them.  All fossil hunting families are not alike.  This mutual enterprise has bound some families together; for others, fossils have contributed to familial discord and dissolution.  This posting is not about many families, but about one family, and, indeed, about a single photograph.

Circa 1913, that’s the best estimate of the Smithsonian archivists for the undated picture of three members of the Walcott family – father, son, and daughter – working away at pieces of the Burgess Shale, high in the Canadian Rockies, near the Continental Divide.  In the photograph below, they are, from left to right, Charles Doolittle Walcott (1850 – 1927), Sidney Stevens Walcott (1892 – 1977), and Helen Breese Walcott (1894 – 1965).  (Photograph is in the Smithsonian Institution Archives, SIA2008-1906.)

I love this photograph.  It is to be treasured for many, many reasons.  Let’s deal with the site first.  Though I recognize its importance, that’s not actually among the most compelling aspects of this image for me (I suspect I may be a minority of one).  The Walcotts first came upon this site in August, 1909, toward the end of a long season of fossil hunting in the Rockies.  Myths have grown up around its discovery, most of which were put to rest by paleontologist Stephen Jay Gould in Wonderful Life:  The Burgess Shale and the Nature of History (1989) and, with a bit more detail, in an essay titled Literary Bias on the Slippery Slope, published in Bully for Brontosaurus (1991).  As for the find itself, Gould waxed enthusiastic.
Without hesitation or ambiguity, and fully mindful of such paleontological wonders as large dinosaurs and African ape-men, I state that the invertebrates of the Burgess Shale, found high in the Canadian Rockies in Yoho National Park, on the eastern border of British Columbia, are the world’s most important animal fossils. . . . These Canadian fossils are precious because they preserve in exquisite detail, down to the last filament of a trilobite’s gill, or the components of a last meal in a worm’s gut, the soft anatomy of organisms. (Wonderful Life, p. 23 – 24.)
Paleontologist Ellis L. Yochelson went Gould one better, writing
To put it as briefly as possible, the Middle Cambrian Burgess Shale may be the single most important fossil find ever made.  (Smithsonian Institution Secretary, Charles Doolittle Walcott, 2001, p. 43.)
The essence of the importance of these fossils can be captured in the phrases “Middle Cambrian” and “soft anatomy.”  This Middle Cambrian array of fossils captures the richness of the marine fauna that marked the so-called Cambrian explosion when multi-cellular life first appears in the fossil record.  It’s a critical time.  And by preserving not just the hard parts, which comprise most fossils, but also the soft parts, these offer a rare look at the physical totality and the lives of these often bizarre creatures, some of which remain well outside of our taxonomic “boxes.”  (I choose to skip over the issue of interpretation of these fossils – what they were, how best to reconstruct them, where they fit taxonomically, . . . .  All of which brilliant paleontologists have wrestled with for years, interpreting and reinterpreting, and often arguing with, and sometimes maligning, those who came before.)

No, for me, it’s not the site pictured in that photograph that is primary, it’s the family engaged in uncovering fossils.  Fossil hunting was a family affair for the Walcotts, a tradition dating back to the honeymoon that Charles spent with Helena (1858 – 1911).  “After the reception, the couple left to begin their honeymoon, otherwise known as fieldwork.”  (Ellis Yochelson, Charles Doolittle Walcott, Paleontologist, 1998, p. 231.)

If this is indeed 1913, then Charles was in his sixth year as Secretary of the Smithsonian Institution and spending his summer and early fall as he loved to, doing fieldwork with his family.  Son Sidney was home (well, actually in the Rockies) from Cornell University, and daughter Helen had just returned after spending more than a year in Europe.

I like to think this photograph was taken the afternoon of September 11, 1913.  The weather had not cooperated that year while the family was at the Burgess site and one of the major undertakings of this fieldwork was extending the Burgess quarry, a task involving the removal of massive amounts of overburden as the layer of fossils was followed back into the hillside.  At the moment captured here, the weather seems good and rock moving is clearly not what’s going on.  Walcott in his diary described September 11th this way,
Up at quarry cold & unpleasant in the morning & cleared up in the afternoon.  We found some fine fossils.  (Smithsonian Secretary, p. 126.)
There is tragedy behind this scene.  Missing is Helena, mother of these children, and Charles’ boon companion in life, most specially in pursuit of fossils.  She had been there in 1909 when the Burgess Shale first came to light, but two years later had perished in the wreck of the Federal Express train at Bridgeport, Connecticut.  Also missing is the eldest child of the family, Charles Doolittle Walcott, Jr. (1889 – 1913), who had died just that April, succumbing after a protracted battle to what was diagnosed as typhoid.

For me, coming to this photograph now, I feel a strong urge to fix these people here, even in this tragic moment, even though mother and brother are no longer with them.  They do not know there is more to come.  Though he was in the Rockies with the family that year, Charles’ youngest son, Benjamin Stuart Walcott (1895 – 1917) was not before the camera.  Just four years later, Stuart’s plane would be shot down in an air battle over France.

Probably Charles, Sr., Sidney, and Helen assumed poses for this photograph, but I deliberately choose not to believe that.  Rather, I naively accept this image as something candid.  A moment on a ledge in the Rockies where all three are fixated, so focused on the task at hand that they are removed from the tragedies they are living through (and that which we see coming for them).  It’s a kind of moment I’ve described several times on this blog, that moment during the search for fossils (and it can occur with many, many other actions we undertake) when time stops, when everything else recedes, and you are in what psychologist Mihaly Csikszentmihalyi has called flow.  (Flow:  The Psychology of Optimal Experience, 1990.)  (I was put on to this literature about flow by a reference in Jack Hitt’s Bunch of Amateurs, a book discussed in the previous posting in this blog.)

Csikszentmihalyi has described flow this way.
Concentration is so intense that there is no attention left over to think about anything irrelevant, or to worry about problems.  Self-consciousness disappears, and the sense of time becomes distorted.  An activity that produces such experiences is so gratifying that people are willing to do it for its own sake, with little concern for what they will get out of it, even when it is difficult, or dangerous.  (p. 71.)
It’s that very separation from your life that gives this experience value, particularly when that life seems unrelenting in its tragedies.  The optimal experience can be restorative, psychologically and physically.  I hope it was for them.

I appreciate the power of photographs to speak across time, to preserve, reveal, and, in some way, restore life.  In that spirit, I close with another photograph.  This one is of the entire Walcott family, before the Burgess Shale, before death intervened.  Here are husband and wife, and their four children in “Olmstead,” near Provo, Utah, circa 1907.  From left to right, standing, are Sidney, Charles, Jr., Charles, Sr., Helena, and Stuart.  Helen is seated in front.  (The photograph is in the Smithsonian Institution Archives, SIA2009-0983.)

Wednesday, May 23, 2012

Just Amateurs

I have been exploring a small clutch of early Eocene marine fossils from the Fisher/Sullivan site in Virginia.  During the early Eocene, this site was shallow, near-shore marine, under the western edge of the Atlantic, and in a markedly warmer climate.  It’s an estimated 53.6 to 52.8 million years old.  To paleontologists – amateurs, professional, or otherwise – this has been a magical site, producing “by far the best sample of early Eocene vertebrates and land plants so far found in Virginia or Maryland . . . .  More than one hundred species of vertebrates now are known from this one horizon, but even so, many more species probably remain to be discovered.”  (Robert E. Weems and Gary J. Grimsley, Introduction, Geology, and Paleogeographic Setting, in Early Eocene Vertebrates and Plants from the Fisher/Sullivan Site (Nanjemoy Formation) Stafford County, Virginia, edited by Weems and Grimsley, and published by the Virginia Division of Mineral Resources, Publication 152, 1999, p. 1.)

Though a wealth of fossils from sharks and other marine animals has been found, a significant source of the paleontological importance of the site are the fossil remains of mammals, as well as fruits and seeds, found here, presumably washed out to sea from nearby land.  These give a rare glimpse into life on land in the Atlantic coast portion of North America during this period.

The site is commonly referred to as Muddy Creek, though it’s actually located on an unnamed tributary of said creek.  The name Fisher/Sullivan refers to the land owners.  I have never laid eyes on the place or enjoyed the rigors of digging and screening there, but from what I’ve heard from those who have, it well deserves that adjective – “muddy.”

I have been working on a few ounces of material that were already washed and screened, and every bit of these few ounces is small fossilized material, including shark teeth, pieces of sting ray dental plates, fish vertebrae, possibly some fish teeth, and what I believe are a few coprolites (fossilized poop).  Most of the teeth are very small and some of those are wonderfully intact, still bearing delicate cusplets (secondary crowns) along side their main crowns.  When one realizes that during the course of its active excavation, beginning in 1990 and leading to the publication of the volume cited above, over 100,000 fossils were found at this site, another adjective is clearly deserved – fossiliferous.

The examples below give a sense of some of what I have in just a few ounces.  The teeth shown in the first photo are:  at left, Serratolamna lerichei (Casier 1946) (12.2 mm height); in the middle and elevated, Abdounia beaugei (Arambourg 1935) (2.3 mm height); and, at right, Abdounia recticona (Winkler 1873) (5.5 mm height).  The second photo provides a sense of really how minute these teeth can be, showing the A. beaugei specimen next to a dime.  (I relied on Bretton Kent's chapter titled Sharks from the Fisher/Sullivan Site, in Early Eocene Vertebrates and Plants from the Fisher/Sullivan Site for these identifications.  Of course, any errors are mine alone.)  [Later edit:  Someone who knows the Muddy Creek fauna well suggested I look more closely at the crown of what I called A. recticona and compare it to images of A. recticona on (Nanjemoy fauna).  He's right, I got it wrong.  We'll see what he suggests it actually is.]

Frankly, it’s not the fossils that I find most interesting about Muddy Creek (though they are amazing), it’s the how amateurs and professionals interacted in bringing these fossils to light.  I’m basing my description of this process on two accounts, one by Weems and Grimsley in Early Eocene Vertebrates and Plants from the Fisher/Sullivan Site, and another by Dick Grier, Jr. in a history of the Maryland Geological Society that appears on the MGS website.

According to Weems and Grimsley, the site was first explored in 1990 by Richard Brezina who recognized its importance, given the wealth of material he was uncovering along the stream.  Subsequently, Brezina turned to his fellow members of the newly formed MGS, a club of amateur and professional collectors of fossil and minerals.  [See comment below from Brezina clarifying that he was not a member of the MGS.]  As MGS members worked the site, screening stream sediment, the actual source of the vertebrate fossils emerged, a geological rock group that heretofore had yielded few such fossils.  To those collecting here, “it seemed reasonable to suspect that this locality was scientifically important.”  (Weems and Grimsley, p. 1.)

After gaining permission from the landowners for an organized exploration of the site, “over a period of several years, members of the MGS excavated tons of sediment from the fossiliferous layer and washed them through screens to extract the fossil content.”  (Weems and Grimsley, p.1.)

Faced with the daunting task of describing the massive collection of fossil material brought out from the site and so making it available to science, MGS members enlisted the aid of several professional scientists to describe different parts of the collection.  Their analysis and description of the fossil finds make up the content of Early Eocene Vertebrates and Plants from the Fisher/Sullivan Site.

The process that led to published report on the site suggests that it featured a remarkable confluence of well-minded amateurs and professionals.  As Weems and Grimsley describe it:
Thanks to a unique and remarkable display of cooperation among land owners, amateur collectors, professional paleontologists, and the Virginia Division of Mineral Resources, this volume for the first time offers a rich and detailed picture of the life and environment that existed in Virginia during the early Eocene epoch.  (p. 1-2)
Grier’s account of what transpired at Muddy Creek will wait in the wings while I comment for a moment on Jack Hitt’s new book Bunch of Amateurs:  A Search for the American Character (2012).  (I read the Kindle version which has no page numbers and so must dispense with page references below.)  Hitt writes for Harper’s, GQ, and The New York Times Magazine, among other publications, and also contributes to NPR’s This American Life.  Scott Simon’s interview with him on NPR’s Weekend Edition for Saturday, May 19, 2012,  put me onto the book.

The hypothesis of this somewhat eccentric work is that at the heart of the American character is a spirit of the amateur, the one who is outside the accepted canon or orthodoxy and, so, sees things differently and is willing to try the new and unusual, sometimes with profound results.  Hitt writes of the
amateur’s childish spirit, of liberty, of leisure – the emblem of the lightness of being, where creativity thrives.  It can be American, not out of nationalist pride, but because this sense emerged at our founding and is the inheritance of anyone born or driven to come here.
The act of the amateur, according to Hitt, accords with the “pursuit of happiness,” leading him or her
to abandon one’s past and one’s self, as well as one’s culture, tradition, and history.  To walk away from everything that one is – whether it’s fleeing a repressive nation for this new place or simply out the back door for the garage – that is the real freedom.  It’s a story that everyone who lives here or comes here recognizes in their gut is true, that the amateur’s dream is the American Dream.
Hitt defines the amateur as “simply someone operating outside professional assumptions” but claims there is an American versus European distinction to be made in what is meant by the term.  In the latter, the amateur may at times have credibility but is usually and clearly sitting “below the salt” from the credentialed professional.  In contrast, Hitt asserts, amateurs in America occupy a broad spectrum that ranges from the kook to the nigh on professional.  Ours, he posits, is a more understanding and accepting view of the amateur, seeing the amateur in two basic forms – someone aspiring to break into the professional tower or someone turning her back on the tower and going her own way.  Frankly, though, in pursuit of his argument, Hitt often equates the amateur with the tinkerer/inventor who is indeed working in the garage to fashion the next break through.  It's a narrow view of amateur.

Hitt weaves his theme through a collection of essays exploring the doings of a very disparate collection of so-called amateurs who are engaged in challenging the status quo be it in such arenas as astronomy, bioengineering, archaeology, robotics, ornithology, or history.  These stories of amateurs are enlightening, amusing, and puzzling.  Who cannot take pleasure from the energy and glee that these folks bring to their tasks?  Be it Meredith Pattern assembling McGivered equipment in her kitchen in order to accomplish the bioengineering feat of injecting a gene responsible for phosphorescence into bacteria that will, in turn, make yogurt that glows in the dark; or the voice of the amateur David Sibley whose expertise allows him to say the ornithological establishment has no clothes when it comes to the ivory-billed woodpecker’s reappearance.

But, frankly, these stories remain puzzling to me.  I'm not sure what to make of this mixture of dreams and quirks that never quite gels into the proof of his hypothesis.

I read this book looking for his insight on the role and contributions of the amateur to science, and there is a bit.  He acknowledges that astronomy and paleontology are among disciplines “just teeming with amateur passion right now and long have been.”  But when he considers what amateurs are doing in the sciences it’s to focus on those who are in pursuit of big idea, the thesis that will come out of left field and knock the establishment for a loop.  His view is one of us (the amateurs) versus them (the professional), and the them are the stereotypic insiders with their hands on the levers of the establishment, working for money and status, jealous of position, fearful of outsiders.

What a depressing picture that is of the professional, and I think it's patently unfair.  The notion of the “pursuit of happiness” being a defining aspect of the American amateur implies that it’s the amateur with the unbridled enthusiasm, the face that lights up when he or she discusses what’s up.  That doesn’t square with the professional historians (my field of training) or professional paleontologists (my wanna-be field) I’ve met.  They are frequently open in their delight with new ideas, happy to explore and explain, often welcoming of the amateur, indeed, particularly for the paleontologist, acknowledging dependence upon the amateur.  Hard to square with Hitt’s perspective.

Though I found the book interesting, it offers a slim array of evidence upon which to expound about the “American character.”  What it did do, at least, was to force me to think more fully about the role of the paleontology amateur.  Yes, there are outsiders banging on the castle gate in the mix.  Hitt writes of Jack Horner, a renowned dinosaur expert, who is not professionally trained, and so is an amateur in Hitt’s eyes, despite the decades of expertise he has built up, the science he does, and the publications he has written.  What attracts him to Hitt is that he is an iconoclast, planting idea-bombs in the foundations of the establishment, such as his view of the Tyrannosaurus rex as a scavenger, not the lawyer-eating predator of Jurassic Park.  I have my own favorite iconoclast in Joan Wiffen, about whom I’ve written previously.  She was the New Zealand housewife turned paleontologist who overthrew scientific orthodoxy when she proved conclusively that dinosaurs had inhabited New Zealand during the Cretaceous.  As she put it in an interview, “I was too ignorant to know that dinosaurs officially never existed in New Zealand.”  (Jack McClintock, Romancing the Bone, Discover Magazine, June, 2000.)

But that’s not the vast majority of amateur paleontologists who, when their paleontological interest expands beyond the thrill of the hunt (which never actually goes away), are likely to take steps to emulate the professional paleontologist, and, in their heart of hearts, seek to contribute to the scientific enterprise if they can.  We’re not a bunch of barbarian at the gates.  In fact, often there are no gates and whatever arms there are, are often open arms.  Indeed, I guess I believe there’s much more of what Hitt characterizes as the European vision of the amateur (“an earnest and uncredentialed aspirant”) alive in the United States than he would admit.

Now’s the time to bring the Grier account in from the wings.  Already the Muddy Creek story is one that seems to center around real paleontological work by dedicated members of a fossil club, mostly amateurs, and willing collaboration with professionals.  (Yes, one could argue that the amateurs held the upper hand since they had excavated the site, but that does nothing to gainsay the productive coming together of amateur and professional in this instance.)  Grier’s account does introduce some of the messy dynamics that one expects to arise in this kind of endeavor, but interestingly, it’s not amateur versus professional.

As I interpret Grier, a threat to the successful excavation of the site arose when the actual source of the fossils was discovered to be above the water level in the stream.  Screening stream sediment for fossils, a process largely benign for the stream, was quickly superseded by digging into the stream banks, something potentially far more damaging to locality.  Grier describes how this shift in focus went down,
The site was located on private property, but the landowners were friendly to collectors, for the most part, and nothing was usually said about the parking and the digging. Within 3 years the stream bed had been effectively "worked out", as others, one at a time were invited to dig at this site. Later, [two MGS members] discovered that the source of the teeth was local, and they were in the stream banks above water-level. This started a landslide of digging activity by everyone.
Landslide of digging activity.  I relish the phrase, as I do the throwaway line about the friendliness of the landowners to this activity on their property for the most part.  Clearly there was conflict brewing involving landowners and collectors, and it came to a head.  Here’s Grier on what happened.
Although I was never exposed to this, there had apparently been some minor scuffles between the landowners and certain individuals, and for a while the site was "off limits" to all collectors.
But in a move that speaks volumes about the relationship between amateur and professional in this effort (so there, Jack Hitt), the amateurs turned to professionals to defuse the situation.
The MGS members asked Dr. Weems to intercede for them with the landowners and to negotiate for some [sort] of compromise. . . . [F]inally it was decided that 15 members were to have "collecting privileges", and their names were placed on a list.  Everyone else, unless they were a guest of these 15 people, would be considered guilty of trespassing.
Marvelous.  Not sure what Hitt might make of this.

[Note on later edit:  I've corrected repeated misspellings of Hitt's name that appeared when the post was first uploaded.]

Saturday, May 12, 2012

Questioning Robin's Eggs

My sojourns out-of-doors often generate questions that lead to protracted stays indoors pursuing the answers.  How counterproductive.  This post is the result of such a stay inside.

‘Tis the season for encountering robin’s eggs, well, broken shells mostly.  Such encounters trigger two questions for me.

  • Why are robin's eggs blue or blue-green?  Let me rephrase that one.  What purpose does their bright, beautiful color serve?
  • Where’s the nest from which these eggs came?  Scanning trees and bushes in the very immediate area has never been fruitful for me.
Clearly, I'm not alone in this.  For instance, in a recent Urban Jungle article in the Washington Post titled The Bluer A Robin Egg The Better (May 1, 2012), Patterson Clark skates lightly over these same two issues.

(The picture of an American robin was taken by Bruce Finnan and is used with his permission.  The pictures of an egg are mine.)

Why This Color?

It is to Charles Darwin and the theory of evolution that we must attribute the asking of “why” questions in natural history and their serious, scientific exploration.  This question regarding the color of birds’ eggs is no exception.  As biologists Philina A. English and Robert Montgomerie have written:
The adaptive significance of avian egg colors has fascinated naturalists ever since natural selection was first used to explain the characteristics of wild species.  (Robin’s Egg Blue:  Does Egg Color Influence Male Parental Care?, Behavioral Ecology and Sociobiology, Volume 65, 2011.)
Naturalist Alfred Russel Wallace, whose brief paper of 1858 on the role of natural selection in evolution memorably forced Charles Darwin’s hand, posited in a much later book that the myriad colors of birds’ eggs were all, or nearly all, selected for their camouflaging properties.  Even those dramatic, vivid colors, Wallace argued, could be, in a biological sense, cryptic.
The colours of birds’ eggs have long been a difficulty on the theory of adaptive coloration, because, in so many cases it has not been easy to see what can be the use of the particular colours, which are often so bright and conspicuous that they seem intended to attract attention rather than to be concealed.  A more careful consideration of the subject in all its bearings shows, however, that there too, in a great number of cases, we have examples of protective coloration.  (Darwinism:  An Exposition of the Theory of Natural Selection With Some of Its Applications, 1889.)
He quickly dispensed with any notion that “the beautiful blue or greenish eggs of the hedge-sparrow, the song-thrush, the blackbird, and the lesser redpole” might actually draw unwanted attention the eggs.  When viewed from a distance in nests in their natural surroundings, he asserted, they “harmonise very well with the colours around them.”

Then he employed a clever debating ploy to buttress his position, though this stratagem may be one possibly grounded in the actual workings of evolution.  In essence, Wallace argued that, if the colors that some birds’ eggs exhibit today might be somewhat counterproductive and ineffective as camouflage, that’s only because we are catching the process of natural selection in midstream – it’s always a work in progress.  He noted that “changes that occur in the conditions of existence of birds must sometimes render the concealment less perfect than it may once have been.”  But, he continued, birds are capable of responding to threats arising from this quarter, through a change in egg color, the nest, or parental care.

Wallace’s position on egg colors has its contemporary adherents.  For instance, ornithologist Yoshika Oniki, in Why Robin Eggs Are Blue and Birds Build Nests:  Statistical Tests for Amazonian Birds, (Ornithological Monographs, No. 36, 1985) argued that “[t]he main function of egg color in the birds I studied seems to be protection against predation.”  This even applied to the blue-green of robin’s eggs – “normally a protective coloration in situations of contrasting light on green foliage.”  Though biologist Frank Götmark concluded that the color blue in song thrush eggs is most likely now a neutral trait, that is, neither serving to protect the eggs from predation or making them vulnerable to it, he aligned himself with part of Wallace’s account:
It is possible that blue eggs evolved in the song thrush (or in the ancestor of today’s Turdus species) in a habitat type different from the one studied here, where blue eggs did provide camouflage.  (Blue Eggs Do Not Reduce Nest Predation in the Song Thrush, Turdus philomelos, Behavioral Ecology and Sociobiology, Volume 30, 1992.)
Nevertheless, much of the current thought on the role of coloring in birds’ eggs and, specifically, with regard to blue or blue-green eggs, has moved markedly away from a sole focus on the camouflaging role and embraces a richer, more complex array of possible explanations.  Among the other general hypotheses for eggshell coloring and patterns are the following:

  • They reflect the maternal addition of substances that strengthen the eggshells.
  • They protect the developing embryo from the effects of sunlight (e.g., acting as temperature controls or shields against UV rays).
  • They better enable parents to distinguish their eggs from those added to the nest by parasite birds.

Some doubt that it’s a matter of choosing among the various proffered explanations.  As biologist Phillip Cassey has noted, “[A] single hypothesis is unlikely to explain the wide variety of eggshell colours and patterns observed across avian lineages.”  (Cassey, et al., Eggshell Colour Does Not Predict Measures of Maternal Investment in Eggs of Turdus Thrushes, Naturwissenschaften, Volume 95, 2008.)

For blue-green eggs, such as those at hand from the American robin (Turdus migratorius), the debate so far has been particularly protracted, vigorous, and, to my mind, inconclusive.  (By the way, turdus doesn’t mean what my scatological view of the world would have it.  Rather, it is from the Latin turd (pause) which means “a thrush.”)

In their analysis, English and Montgomerie (cited above) noted that “blue-green pigmentation has long defied explanation.”  A situation they have sought to remedy.  They identified biliverdin, a bile pigment (it appears in bruises on our skin), as the main agent responsible for the blue-green egg color.  Biliverdin is an antioxidant and important for maternal health.  Its infusion into eggs comes at a cost to the female and, so is likely to provide some countervailing benefit.  English and Montgomerie suggested three possible reasons for this expenditure of biliverdin by those species with blue or blue-green eggs:

  • The pigment might function to shield the embryos from deleterious effects of sunlight, but they stress this doesn’t preclude the pigment providing other services for which it was selected (for a description of the findings from a recent analysis of this possibility, see Brandon Keim’s piece titled Debate Over Purpose of Bird-Egg Coloration Continues, in Wired Science, September 22, 2011).
  • Laying eggs that are particularly noticeable may “blackmail” the male partner into a more active role with regard to egg incubation or feeding the female while she incubates the eggs, but English and Montgomerie note that this would apply only to those species where males actually perform these functions.  (I really like the Machiavellian nature of this hypothesis.)
  • A female’s significant infusion of biliverdin, resulting in more vivid eggs, may signal to her male partner that she is exceptionally health and that her developing offspring will be robust.  This signal, it is argued, will generate greater attention by the male to the survival of the hatchlings.

It is the last of these hypotheses – the sexually selected egg color (SSEC) hypothesis – that English and Montgomerie explore in their article, Robin’s Egg Blue:  Does Egg Color Influence Male Parental Care? (see link above).  They are not the originators of this hypothesis, but are among the most prominent voices in its support.

I found their particular study fascinating, both for the methods they used to test the hypothesis and how they dealt with the challenging results they obtained.  In the study, they monitored American robins’ nests, some of which they manipulated by replacing some of the eggs soon after they were laid with pale or particularly vivid artificial eggs.  As soon as the real eggs hatched, the artificial eggs in the experimental nests were replaced with unrelated robin hatchlings.  They then monitored the parental behavior, with a focus on male provisioning of the nestlings.

After analyzing the results, they concluded:
In this study, we provide a clear, experimental demonstration that male American robins adjust their nestling provisioning rates in response to the vividness of the blue-green color of their mate’s eggs.
No doubt being expressed there.  A strikingly robust conclusion.

Unfortunately, immediately after making that statement, the authors spend the remainder of the paper backtracking because the data they generated only weakly support that assertion.  The strongest evidence in support of that bold  conclusion was that “[m]ale robins who saw more vividly colored artificial eggs in their nest fed 3-day–old nestlings almost twice as often as those who saw pale eggs, controlling for other variables.”

But there’s the rub – the critical response by the males was correlated with nests containing the vividly colored artificial eggs.  In fact, the control group of nests, those that were not manipulated, held eggs exhibiting some variation in color intensity (though not of the extremes used for the artificial eggs) and male investment responses to those natural color variations were only very weakly correlated to color.  Further, even for the nests with the artificially vivid blue eggs, the effect on male investment disappeared by the sixth day after the babies broke out of the eggs.

The authors worked to defend the SSEC hypothesis from their own findings, expressing how “puzzling” they found the results in the control group of nests.  Not surprisingly, their descriptions of the possible explanations for these results did not preclude sexual selection on the basis of egg color from playing a role.  Ultimately, though, as they closed the paper, they wrote,
While a weak correlation between male provisioning rates and egg color support the SSEC hypothesis, other adaptive (and non-adaptive) explanations for the blue-green color of American robin egg [sic] cannot be ruled out.  For example, blue-green pigmentation due to biliverdin might sometimes be cryptic, may provide some protection from solar radiation, or could help strengthen the eggshell.  (Cited references omitted.)
These findings might not be surprising to Frank Götmark (cited above) who concluded that the blue color was probably a neutral trait.  Further, the results for the control nests are consistent with those of Cassey (also cited above) who found that the blue-green color in the eggs of the species they studied had only a weak correlation with their various measures of maternal investment in the eggs.  As a result, they argued, color variation would be “unlikely” to function as a signal to males of the quality of the female and the eggs.  As I understand that analysis, in their eyes, so much for the SSEC hypothesis.

Well, we’re left with several working hypotheses without any single one, in my reading of the literature, rising to the top.  Given how uneasy I am with bold, take-no-prisoners statements, I really like Frank Götmark’s conclusion:
Thus, there are no simple explanations.  If we assume there is a cost of producing blue pigment, it is likely that blue eggs are in some way adaptive.
More research is in order.

Where From?

Ah, this one’s apparently a lot easier to answer.  Ornithologist Joseph C. Howell provided a response in his Ph.D. dissertation, which was published in an abbreviated version in as Notes on the Nesting Habits of the American Robin (Turdus migratorius L.) (American Midland Naturalist, Volume 28, Number 3, November 1942).  Presumably this was not the first time it was described.
The shells from which young Robins have hatched are removed from the nest almost as soon as the young are free.  The fate of the shells is not always the same.
Often, he observed, the females ate the shells.  Though I don’t know about the broader prevalence of the eating of the empty shell, the policing of the nest to remove the eggshells soon after hatching is not unique to robins.  Of course, in our Darwinian world, this raises the question, why?  In his Urban Jungle article (cited above), Patterson Clark asserted that this action was prompted by the white insides of the broken egg which might attract predators.  He linked to an essay on empty shells that appeared originally in The Birder’s Handbook by Paul Ehrlich, et al. (1988).

And questions beget questions.  For the robin parents, is the white interior of a broken eggshell more problematic than the blue exterior?  Does it make a difference where the eggshells are dropped?  Might there be some premium on dropping those conspicuous eggshells in the territory of some other nesting robin pair or some other competing species?  Is it only the female who removes the eggs as various accounts would have it?  How common is it for the female to eat the eggshells?  Might she be doing it to recover some of the resources she invested in the eggs?

I think it’s time to go outside and watch some robins.

Later Edit

Amazing what a hobgoblin occupied my mind as soon as I uploaded this post.  I've been grappling with what quite possibly should have been the first question considered here - Is "robin's eggs" grammatically correct when I'm using that phrase to describe the eggs of robins in general, not the eggs of a specific robin?  Or should I have written "robin eggs" or, perhaps, "robins' eggs"?  (Should that last question mark have gone inside the end quotes?  Sigh.)  Upon reflection, I believe I should have opted for the phrase "robin eggs" if only to be consistent with my usage of "shark teeth" elsewhere in this blog.  As a middle school teacher once told me when I noted she'd missed an error on one of my test papers (yes, I was that kind of student), "We progress, we don't digress."  So, if error this is, I will leave it and move on to something else.
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