Flashy color and honest signals

19 01 2016

After the last Dead Bird Quiz featuring blue wing patches, it seems an apt time to address the structure and function of such color in birds. Blue is, of course, not the only color a bird may display; even outside the outrageous coloration seen in many tropical species like parrots, we here in North America are treated to many birds in these color classes:

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Male scarlet tanager in Illinois (photo: CheepShot via Wikimedia)

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Baltimore oriole depicted in the Wisconsin Bird Bulletin, 1906. (photo via Harvard’s Ernst Mayr Library)

In such cases, the colors in the feathers are built from dietary pigments, particularly carotenoids. Because the brightness of the color in the feather depends on the quality of the diet, such reds and oranges are termed “honest signals” of the quality of the individual–birds that are better foragers sport brighter colors. A female selecting a mate can use the brightness of a male’s plumage as an indicator of what sort of provider he will be, both in terms of genetic contribution, and, in species where males contribute parental care, how well he will provision the chicks.

Blue pigments, on the other hand, are not derived from diet, but are instead what are known as structural pigments. Proteins in the feather, when aligned properly, will reflect blue light back at the observer. These proteins typically “self assemble” and a more genetically fit bird would not be bluer than a lesser individual. Blue feathers either are, or they aren’t, as the conventional wisdom goes, and there is no spectrum of brighter or duller blue jays, or ducks, or what have you. There has been work to challenge this, focusing on what can affect the brightness of structural color. Feather mites, for instance, could damage or dishevel the feather, leading to a loss of brightness. A more fit individual might have fewer such parasites, and so the blue in these birds might appear brighter than a heavily infested bird. So a duller bird might be less fit, but is there any such thing as a “super blue?” A blue that is brighter than the average because that bird is fitter?

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Turquoise-browed motmot (photo by Katja Shulz, via Flickr)

I encountered a study done on turquoise-browed motmots in Mexico on this subject. In this species, both males and females sport a blue tail with a racket shaped projection at the end, though the tail feathers are longer in males. The researchers analyzed the brightness of the tail feathers across the sexes and within the sexes, between individuals. They were interested in determining whether the brightness of the blue could, in fact, be linked to fitness in either or both sexes. Not only did the study address the variation in brightness across individuals, they also measured how quickly the feathers grew. Growth rate is considered an indicator of fitness since a bird’s energy reserves, and thus diet, determine how much new feather a bird can lay down in a day.

The research team indeed found that the brightness of the blue in the tail feathers was greater in birds whose tails grew faster, but only in males. In females, no link between the two was identified. It seems that, in males, blue may indeed be an honest signal of fitness. In females, the tail is shorter overall, and there is no correlation between brightness and growth. This is consistent with the hypothesis that the tail in female motmots is not used to signal fitness, but may serve a different purpose, like distracting predators while the bird makes a swift escape, or may simply be a genetic holdover between the sexes.

This subject of honest signaling also came up while I was preparing notes for a new course I am teaching this semester. My students will be looking at the dominance hierarchy in house sparrows. In these birds, the size and darkness of the bib in males is an indicator of his position in the hierarchy. Both males and females will defer to larger-bibbed males, and the dominance extends not only to access to mates, but to nest sites and food. Researchers have understandably been interested in what underlies these bibs. The black color of the bib is caused by the pigment melanin, which is expensive to manufacture. Because of this, black coloration is considered an honest signal, much as reds and oranges are, since only a well fed, highly fit individual, would have the spare energy to lay down that pigment. Since the bibs are tied to dominance behavior in males, testosterone seemed a likely target for analysis in this case. Interestingly, I found one study that showed no link between high testosterone and large, dark bibs. That study also noted that the bib is produced in fall when the birds molt, but is not used in terms of mate selection until the following spring. Testosterone levels can fluctuate substantially over that time, so birds that had high circulating testosterone in fall when they grew the bib may well have lower levels than their rivals come spring. So if females use those badges to select mates, and if rivals are choosing not to challenge another male based on badge size, they are not using a reliable indicator of testosterone at the time of breeding either.

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A modest throat patch. Dark bills, unlike badges, DO show a clear link to testosterone levels. (photo: Adamo, via Wikimedia)

A more recent study following up on this work looked at testosterone again, but measured it at night rather than during the day. The results indicated that testosterone was, in fact, linked to badge size. Over the course of 24 hours, testosterone levels peak at night while the birds are asleep, and fall off rapidly as soon as the birds wake up. When measured at night, peak testosterone levels did correlate with individuals with the largest bib size. Perhaps, suggest the researchers, badge size reflects peak production of testosterone, rather than average level. This still leaves the question of seasonal changes–does this nighttime testosterone production hold true for the time of year when the badges are being grown, or only during the season when they are being used for breeding signaling? The plot thickens. Or, since we’re talking about dark splotches on birds, shall we say, the blot thickens? Sorry.





DBQ answers

12 01 2016

I got quite a few responses to this one, and I am not surprised that our usual ringers were right in here with both the clear i.d.s and the one that is, at least somewhat, in question. All three birds are ducks which all respondents recognized. The first two are in one category–ducks with a bluish speculum on the wing. Bird C is in a category of ducks with blue on the wing, but with that blue located on the upper wing coverts rather than the secondaries as in Birds A and B. Let’s take the Bird A/B pairing first.

I like when I have an all duck quiz since I can use Samuel Carney’s Waterfowl Wing Key. When we follow through that key for a bird with blue or purple on the secondaries, we get to a junction point where we are asked what borders the blue or purple patch. If it is hemmed in with white both above and below (that is to say, with white on both the greater coverts and on the trailing edges of those blue/purple secondaries), then we have a mallard, like such:

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Mallards in flight. (Photo by Ingrid Taylar)

In this photo, one can see not only the clearly bordered speculum, but another helpful feature for when you have the underside of the wing to look at as well–a mallard’s underwing is a clean, clear white. This is in contrast to our other candidate among the blue-speculumed ducks, the American black duck, which has a characteristic brown streaking on the underside of the wrist.

An American black duck (ABDU to friends) is generally described as having no white border, front or back, around the blue, though in many images and in some descriptions, one may see a faint pale trailing edge to the secondaries. It’s pretty faint though. Great, so that was easy, no? White borders: mallard. No white borders: ABDU. Not so fast (0f course). Because these two species heard we were having an easy time of their identification, they decided to hybridize freely. Given the slight chance of pale tips to the secondaries in an ABDU, we can look at the forward border of the speculum for a firmer sense of what is happening here. In an ABDU, there should be no white at all on the greater coverts at that leading edge of the blue speculum. So, where are we now with respect to Birds A and B? A shows substantial white both fore and aft. Bird A looks like a mallard decisively to me (my decisiveness here is augmented by back up from most of our respondents on this quiz). Bird B has what we might technically term a “meh” amount of white on that forward border of the speculum. It’s faint, but it’s definitely there. While some of our quiz players think ABDU on this one, others raised the possibility that this is one of those ABDU x MALL hybrids, and I am inclined to agree. Would that we had more of the bird to go on, but the features here do seem intermediate between the two species.

Now, to Bird C. This one is in the group of ducks with a large amount of blue on the upper wing coverts rather than the secondaries. It’s hard to know if the secondaries ever had much color–they may have, but as my next blog post will address, blues and greens in bird feathers are a trick of the eye, and in a disheveled specimen, those colors may be lost almost entirely. In addition, in some species, the secondaries are green and iridescent in males, but green and non-iridescent (dull) in females. I don’t see much that catches my eye in the secondaries of Bird C at all, but if there is any green there, I would say it looks decidedly non-iridescent to my eye. What we have to go on is the blue, and then some white on the greater coverts, though they do not appear entirely white–more dark spotted with white rims. In the group of birds with blue on the coverts and a white band on the greater secondary coverts, our best candidates are blue-winged teal and northern shoveler (both raised by our respondents). How to differentiate them? The number one feature all the field guides point to are the distinct white shafts of the primaries in northern shovelers. Take a moment to appreciate them in this image:

 

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USFWS photo

As you can see in these images, the white band on the greater coverts in northern shovelers is uninterrupted, unlike the broken band with dark spots we have in Bird C. In addition, I do not see these obvious white primary shafts in Bird C. Taken together, these two features lead me to call this a blue-winged teal, and again, I draw unnatural courage in this i.d. from the fact that it came to me pre-identified by Craig Watson who works for USFWS down south, and also, so many of our crack dead bird experts told me they thought it was a blue-winged teal as well. I hardly ever see these, so I confess, I would not have come up with that right off the bat.

Next time, I will share with you what I’ve been reading about feather pigment, honest signals, and the flamboyant tails of motmots in the Yucatan.





Dead Bird Quiz: got the blues edition

8 01 2016

It’s a monochrome world outside here in the north, and, though I am secretly wishing for snow so I can get some cross country skiing in, I do appreciate a spot of vibrant color. Thus, I have made these selections for the DBQ. Though they are not the most challenging ever, this will give me a window to talk about pigment in feathers when the answers are revealed, so look for that next week.

Here are our candidates (a phrase I hear a bit too often for my liking here in New Hampshire these days; I can’t travel 5 miles without tripping over a would-be President).

Bird A: found by Dan Tracey in Massachusetts in May.

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Bird B: found by Ray Bosse, also in Massachusetts, also in May.

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Bird C: guest Seanetter Drew Lanham, professor at Clemson, photographed this bird on New Year’s Day on Seabrook Island, SC.

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Volunteer profile: Alice Wynn!

30 12 2015

It’s been a while since I brought you all a volunteer profile, readers, so now, at the tail end of 2015, I bring you this note about a committed Seanetter of Cape Cod extraction, Alice Wynn. As with many Seanetters, my only contact with Alice was via email and through reading over her survey data. She was diligent, committed–all the usual things we are accustomed to in our volunteers. I suppose I assumed she was a Cape Cod retiree, as so many of our very best volunteers are. So I admit to feeling surprised when Alice asked if I would write her a letter of recommendation…for college. Alice had always demonstrated such maturity and poise, I just never guessed she was still a teenager.

In any case, I very happily wrote the letter, and Alice, not surprisingly, did get into college (not to suggest that the one was a result of the other). This summer, she got to spend some time up in the beautiful wilds of Downeast Maine, and she sent along a few pictures of her encounters with wild creatures, some quite close indeed, as in this one, showing Alice holding the eyeball of a basking shark!

20150903_090748-2.jpgAlice was also very kind in obliging my request that she write a little note for me to share with you all here on the blog. Alice wrote,

“Prior to volunteering with Seanet, I would frequently examine dead birds that I came across on the beach, so getting the chance to actually submit data on what I came across was a great opportunity for me. Volunteering with this organization has also allowed me to be part of a large-scale scientific research effort that provides crucial information in regard to the health and well-being of coastal seabirds, which is something I am very honored to have the chance to do.

I have always had an interest in biology, with a specific focus on ornithology. Currently I am employed at the Cape Cod Museum of Natural History in Brewster, MA. Volunteering with Seanet has helped me improve my beached bird and general seabird identification skills a great deal. This in turn has helped me not only answer visitors’ questions in this area, but also has helped me to better identify dead birds when I lead field walks.”

In her travels along the coast, Alice also saw some pretty cool birds. My favorites, a species I’ve never seen (alive), are these phalaropes:DSCN4648-2

I have a soft spot for birds like these–the phalaropes and storm petrels, that look far too small and delicate for their seafaring lifestyles. There’s a lesson in that for us all, I suppose.

My thanks to Alice for being one of the people who keeps this program going, despite so little aid or input from me. Now, I leave you with a non-seabird, but Alice and I share an affinity for these airbrushed birds. This time of year, the fruit tree outside my office sometimes seems more heavily laden with waxwings than with the fruit they’re gobbling down. I think Alice has caught this one’s prideful gaze rather well.

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The international shearwater

18 12 2015

Last week, the Science Club at Northern Essex Community College in Massachusetts had a special guest at their meeting. A world traveler joined us, having a last known address in Tenerife, in the Canary Islands. The visitor was a bird, and was, unfortunately dead.

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Here we are doing the dissection. 

This specimen was a female Cory’s shearwater (Calonectris diomedea) and we received it via Friend of SEANET Susannah Corona, who conveyed it to me in a sketchy roadside exchange. The bag containing the carcass did sport a jaunty holiday bow, however.

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The bit of bling carried all the way across the ocean.

Susannah found the bird on a beach north of Boston and managed to track down the banding lab in Europe with the info on it. Turns out, the bird was one of many confused by, or attracted to, the city lights in Tenerife where it struck a building. The bird was rehabilitated and banded prior to its release. Arantza Leal Nebot, a researcher with SEO BirdLife, provided us with this map of band reports. If my Spanish is even somewhat passable, then the blue dots represent where birds were banded, and the small red diamonds show band recoveries. As you can see, Susannah’s find was only the second North American report for a Cory’s ever in this project!

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The findings on necropsy were limited since the bird was rather decomposed. There were a few rib fractures sustained after death, which is consistent with being buffeted around by waves. That, in combination with the decomp suggests that this bird floated around a while after dying and only later washed up. I was able to determine that the bird was emaciated at the time of its death with no fat stores remaining in the body and substantial muscle wasting. The gizzard was empty but for a few squid beaks, and we found no plastic pieces in the GI tract. We often find plastic in shearwater stomachs, though I tend to find fewer or no pieces in birds that appear to have starved to death. It may be that birds who can’t find any food to ingest also aren’t ingesting plastic. This would suggest that the birds tend to pick up the plastic incidentally while feeding rather than mistaking the plastic for food, but that is mere conjecture on my part.

The Science Club students found our dissection day quite rewarding, and we plan to do it again next semester with whatever cool specimens we manage to wrangle up. For my part, I always enjoy a necropsy, but the rewards of introducing students to the interiors of seabirds have given me a new jolt of enthusiasm for the activity. Stay tuned for more such cases next semester when Science Club is back in action.





DBQ answers II

14 12 2015

No more shirking or dodging; I must at last face those wings known as Bird B. To jog your memories, here’s what we’re working with:

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Dennis, who found the wing, wondered if this might not be something other than a standard issue species. Everyone who has looked at the wing (and ventured to reply) concurred that this is a loon of some kind. The clean white underwing by itself could indicate a few different species groups, including shearwaters and grebes. But looking at the upper wing, we see buff colored chevrons at the terminal ends of the secondary coverts. The wing chord looks to be around 28cm. These features together tell us this is a loon, and a pretty small one (common loons have a wing chord in the 33-40cm range). Red-throated loon is the default i.d. for a small loon on the east coast, but it’s not the only possibility. Dennis granted that it could certainly be a RTLO, but thought something just seemed a bit off about in terms of its overall coloration and the nature of those pale chevrons. Since Dennis has seen many, many a dead bird, I think it worth a look when he notes something atypical about a carcass. Dennis thought perhaps Pacific loon should be on our consideration list. If we consider Pacific, we should also consider Arctic since the two are almost always uttered in the same breath and can be difficult to distinguish themselves. Both Arctic and Pacific loons would have a wing chord in the range of Bird B’s; both average larger than RTLO, but a wing chord of 28cm would fit with any of the three species. Strangely, given what one might assume from the names, the Arctic loon would be much more of a rarity than the Pacific in these parts.

This situation calls for the use of two of my favorite resources: Peter Pyle’s identification guide, and the Slater Museum’s online wing collection. You can check out a whole suite of loon wings from various species and times of year here. Fortunately for me, they have a few Pacific loon specimens there to look over, in breeding and non-breeding coloration. As with many loons, breeding plumage includes bold, clear, pure white spots on otherwise black upper wings. Our Bird B does not have any white spots or dots at all, but that lack is typical of a bird no longer in nuptial raiment. Beyond being a non-breeding bird though, what we have here in Bird B appears to be a young bird. In the case of RTLO and Pacific loon, both have pale edges to the secondary coverts during the first year, and that first year plumage is retained into well into the first winter, so the timing is right for Bird B, which was found at the end of November.  To parse out the differences between juvenile RTLO and Pacific loon wings, we can look at Peter Pyle.

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Secondary coverts in Pacific loons. In juveniles, a pale, terminal band gives the impression of light, nearly white crescents over the upper wing.

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Contrast the preceding with these secondary coverts from RTLO. The far left image is a juvenile and the pale coloration here is much narrower and comes to more of a point, giving an impression of chevrons rather than crescents.

Considering this, I am of the opinion that Bird B is decidedly chevroned and now crescented. And so, though I had fervently hoped we might have a first ever Pacific loon in our database, I fear it is not, and is, instead, our old friend the Red-throated loon. As ever though, if I am missing something critical, I know all you super-pros will write it with the correction.





DBQ answers

9 12 2015

Let us address Bird A, who met a bad end (and a Cessna) at 3,200 feet. The head was torn off by the force of the impact, and, left with only the feet and legs, and a bright white belly, we must make this i.d. without the benefit of a look at its back or upper wing surface. Some folks who examined the photos thought perhaps it was an oystercatcher, but looking at the feet especially, we can rule that out.

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Plane Bird feet

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Oystercatcher feet

Comparing the feet side by side, we that Bird A (Plane Bird) has a grayish cast to the legs and feet, with black coloration on the outside aspect. Bird A’s legs are also extremely flattened side to side, with a very narrow front profile. (Compare the width of the side view of the right leg with the left leg which is rotated so we see it head on). This gives the leg a blade like appearance. The oystercatcher’s legs are more rounded, and the extreme lateral flattening of Bird A’s legs is a fair giveaway of what species group we have here, and rules out other black and white birds with more rounded legs (like the alcids). There’s really nothing but a loon that shows this lateral compression of the leg and even toes to such an extent. It’s hard to appreciate the webbing in loons in many cases since their toes tend to fold together in a dead specimen. Take a look at this reference picture of a known loon and compare the features of the feet with Bird A, noting the color, the length of the three forward toes, and the extremely reduced hind toe in both specimens:

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common loon carcass (Photo by Gil Grant)

So the feet say loon, but what kind of loon? Our most likely suspects are common and red-throated (COLO vs. RTLO). Unfortunately, the best ways to distinguish the two are via features of the head and neck (absent here), the measurements (no size reference here), and the pattern of the feathers over the back and upper wing (not visible here). Can we make this i.d. to species with what we can see? Much as I wish otherwise, I do not think so. I was hopeful that something like the black stripe across the vent in Bird A might help, but take a look at these reference photos of various vents from various loons:

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RTLO with very faint dark line across vent. (Photo by Sarah Porter)

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RTLO with basically no vent line. (Photo by Jerry Golub).

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COLO with a fairly prominent vent line. (Photo by Dennis Minsky)

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There are cases (like differentiating Arctic from Pacific loons, apparently) where presence versus absence of a vent line can be your make or break feature. But for us, deciding between RTLO and COLO, it’s not much help. Either species can have a faint or a prominent vent line, so the fact that Bird A has a visible one doesn’t really tell us much.

Live birds flying overhead are sometimes the closest (ironically) we can get to the situation of trying to identify a dead bird from features of its undercarriage, and I refer you to such a case posted at the American Birding Association’s website here. In their analysis of that bird’s i.d., they point to a sense of how big the feet are relative to the body. Common loons have absurdly large feet compared with RTLO, whose feet tend to look more normally proportioned. You can appreciate this a bit when you compare the images above of the feet on RTLO vs. COLO. Which is true of Bird A? Huge feet, or not so huge feet? That’s a bit hard to tell from the angle we have. They seem somewhat outsized to me, but I’m not feeling super confident on that. Bob, who collected the bird from his plane’s wing, submitted feather samples to the Smithsonian for i.d. to species, so hopefully, we will receive word from on high for this one. Bob did email this week to say he has yet to hear from the Smithsonian. Perhaps we should run a letter writing campaign and on site protest bearing signs that read, “Who is Plane Bird!?”

I still have Bird B to address, but right now, I must run to pick up the kids. Next installment will be before your eyeballs later this week, I assure you.

 

 

 

 








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