Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
We continue with the series of Emilio d’Alise’s lovely pictures of swallows feeding their young (see first installment here). Emilio’s captions are indented, and you can enlarge the photos by clicking on them. I repeat some of the intro from the last series.
From 2007 to 2013, I lived in Colorado and worked in Woodland Park (8,100 ft. elevation). We had an empty lot next to the office, and we put up a Bluebird house. For the first three years, we had Bluebirds nesting in it, but in 2011, a pair of Tree Swallows (Tachycineta bicolor) moved in, and returned each year for the next three years. This post from 2011 documents the final weeks before that year’s brood fledged — they all fledged, but a hawk got one of them —and it includes photos and videos.
But, the year that I got serious about photographing them was 2012, and these are some of the photos from those sessions.
As I mentioned, the birdhouse is sized for Bluebirds which are smaller birds, so the typical Tree Swallows brood of 5-7 makes for a pretty tight fit just before they fledge. Early on, the adults will enter the nest to feed the chicks.
. . . On most feedings, a fair portion of the adult’s head goes inside the beak of the chick (both close their eyelids during contact) to ensure the meal is not lost. Still, occasionally, a few bugs fall out before the chick has a good grasp of it, probably because various parts of the bug may be stuck to the adult’s plumage.
On average, I would say at the peak (when I was shooting), the parents were coming by about every one to two minutes.
As far as I could tell, for a few weeks — from early morning to dusk — both adults did nothing but catch bugs and feed the chicks.
Here’s a swallow feeding its offspring a “pretty large bug”: a grasshopper:
Now my own personal observation of mallard ducklings following their mothers in Botany Pond shows that when she’s swimming slowly, a pack of them will clump behind her, as in the photo below (mine):
But when she’s booking it away from other ducks, the babies form a line behind her, like this (not mine):
Some other waterfowl show the same behavior when swimming in open water. Here are a pair of geese and their goslings (one adult brings up the rear as a guard):
Family of Canada geese swim across a pond- mother and father between 3 fluffy goslings
Have you ever asked yourself why? Wouldn’t a clump be better? Well, five researchers from China and Scotland asked themselves what advantage could possibly accrue to swimming in a line?
And they found one: it involves riding the waves of the duck ahead of you, and it benefits every duckling in the line. The phenomena involved are called “wave riding” and “wave passing,” and are explained briefly (and not very satisfactorily) in the short popular piece directly below at Phys.Org, which appears to be a press release from Glasgow’s University of Strathclyde.
Click on the screenshot if you want a quick explanation, but if you want to go into more depth, involving math and fluid mechanics, read the original paper two screenshots down. It’s from The Journal of Fluid Mechanics.
Here’s the original paper (click on screenshot); the entire reference is at the bottom and you can get a pdf from a link on the title page:
The explanation is simple but based on complicated modeling rather than observatin. And although at the end the authors claim that they now understand why ducklings swim in a line, they really don’t. They have proposed a model that, in my estimation, is a good explanation, but one that needs empirical testing. You have to look at the ducks!
Here’s how it works, in a model in which they’ve made some assumptions and used fluid-mechanic equations of drag in the water.
See the diagram below, with the arrows showing the hydrostatic force.
(b) When a duckling is swimming in calm water, its movement is impeded by the water drag alone, and there is “hydrostatic pressure force” that is exerted upward on the duckling’s belly.
(c) When a duckling is swimming on a wave with its breast on the wave’s crest and its belly in a trough, the hydrostatic force (arrows) works against the duckling’s movement, making it exert more energy than if it were swimming in calm water.
(d) However, when a duckling is swimming with its breast in the wave’s trough and belly on the crest, it is propelled forward by the wave, exerting less energy to swim than it would in calm water. It’s like surfing.
(From paper): (b), (c) and (d) shows a sketch of a two-dimensional duckling on a free water surface: (b) stationary in calm water; (c,d) swimming in waves with the same wavelength but different phase. Green curves denote the water surface. Blue curves denote the pressure on ducklings’ immersed body surfaces and the arrows denote the direction of the force.
And this is the explanation for why the first duckling “drafts” behind the mom, for mom’s swimming creates a series of waves behind her. You must assume that the duckling is the right distance behind her and riding the waves in position (d) above (assumptions not tested in the paper). As the authors note, it requires that the duckling’s forward speed must be equal to the mom’s (the velocity of the wave). This is called “wave riding”. But of course the duckling’s speed must equal Mom’s speed if it’s not to fall behind or go ahead.
The mother duck benefits too: she can get a reduction in wave drag of up to 35% by being pushed by the bow wave from the first duckling behind her. It’s a win-win situation.
What about the other ducklings in line? Well, in the “wave passing” phenomenon, the other ducklings get a similar boost in movement so long as they’re the right distance behind the one ahead and so have their breast in the wave trough. All that’s required is that they keep the right distance from each other and move at the same speed as the mother. (They do of course move at that speed: that’s what keeps the line.) The first three ducklings get special benefits, but after that each succeeding duckling gets a smaller but still appreciable (and equal) boost, shown in the figure below (CDR represents the “reduction in drag” coefficient). Don’t ask me why it’s the first three who benefit most; it’s above my pay grade. ‘
Here’s a figure of a mom and six ducklings, showing the reduction in drag of each duckling on the y axis (height of blue dots). Duckling #1 gets the most benefits, then #2 and #3, and then the rest get equal benefits of wave-riding via wave-passing. The red lines show the wave profile.
(From the paper): (b) Wave drag reduction of each individual (blue dash line and columns). The red solid curve is the wave profile on the centre line behind the mother duck. Here 𝑑𝑛,𝑛+1 is the separation between two adjacent individuals, where the subscript 𝑛=0 represents the mother duck. The virtual ducklings are put in the positions of minimum wave drag. The error bar in panel (b) gives an indication of the errors induced by numerical discretization.
There would of course be an evolutionary advantage to babies swimming this way. And of course they don’t do the calculations, but those ducklings swimming the right distance behind the one before (a phenomenon that must itself evolve), have an energy advantage compared to off-wave ducklings, and that means better survival and reproduction. The authors add that “These principles could be potentially applied to design modern freight carrying vessels, e.g. a water-train to transport more cargoes without extra fuel cost.”
So that’s the story. And yes, it is a story, but a good one. How do we test it? It’s not that difficult: you simply measure where the ducks are swimming behind the mother, seeing if they are indeed riding her wave. It’s harder than it looks, but surely not beyond doing! (I should add that a single duckling swimming in front of the mother gets a bow-wave push, but that doesn’t work for multiple ducklings, and there’s a protection and navigation advantage of swimming behind and not in front of Mom.)
It should be tested, for it’s a simply explanation for an observation that many have made, but none have queried.
Here’s one caveat I thought of. We know that ducklings sometimes follow in a line behind Mom when they’re walking on land. Here’s a photo:
There are two questions: does this reflect an advantage different from that of wave-riding and wave-passing? Why aren’t they walking in a clump? And if there’s an advantage of terrestrial locomotion in this way, perhaps the explanation above is wrong or insufficient. On the other hand, my own guess would be that mallards are only infrequently on land with their babies compared to being in the water with them. I suggest, then, that single-file following evolved for water locomotion and is automatically followed as a instinctive byproduct when they’re moving on land. Who knows?
This is exemplified in the famous “Make Way for Ducklings” statue on the Boston Common, honoring the famous children’s book:
Please send in your good wildlife photos if you have them. I have a small backlog but it’s spotty. If you have a polydactylous cat, send two photos (cat and paw) and a few words about your moggy. I can accept them today and add them to the Caturday Felid post that will go up around 9:30 Chicago time.
Today we continue on with photos of tree swallows taken by Emilio d’Alise (see first sequence here). Emilio’s notes are indented, and you can click on the photos to enlarge them. We have three separate feeding sequences, with two more to come in a later post. Without further ado:
From 2007 to 2013, I lived in Colorado and worked in Woodland Park (8,100 ft. elevation). We had an empty lot next to the office, and we put up a Bluebird house. For the first three years, we had Bluebirds nesting in it, but in 2011, a pair of Tree Swallows (Tachycineta bicolor) moved in, and returned each year for the next three years. This post from 2011 documents the final weeks before that year’s brood fledged — they all fledged, but a hawk got one of them —and it includes photos and videos.
But, the year that I got serious about photographing them was 2012, and these are some of the photos from those sessions.
These folders are three different feeding sequences, all shot during my one hour lunch. The camera is mounted on a tripod and pre-focused, and I’m standing about six feet away. It only took about five minutes for the adults to overcome their hesitancy due to my presence. During that time, they made a number of aborted passes, but eventually the insistent chirping of the chicks had them ignore me and the camera.
I could tell when the adults were coming because the chicks switched from chirping to offering their wide-open beaks, at which time I would shoot short bursts. The feeding itself usually lasts no more than one or two seconds unless the adult ‘lands’, usually to offer a larger meal that was more difficult to shove into the awaiting open beak.
On most feedings, a fair portion of the adult’s head goes inside the beak of the chick (both close their eyelids during contact) to ensure the meal is not lost. Still, occasionally, a few bugs fall out before the chick has a good grasp of it, probably because various parts of the bug may be stuck to the adult’s plumage.
On average, I would say at the peak (when I was shooting), the parents were coming by about every one to two minutes.
As far as I could tell, for a few weeks — from early morning to dusk — both adults did nothing but catch bugs and feed the chicks.
Photo Folder: Feeding Sequence 2 – landing and nice launch
Photo Folder: Feeding Sequence 3 – quick
The 2012 Tree Swallow post with these photos and longer narrative (and videos) is at this LINK. The comments on that post also has a discussion about photographing birds and building bird houses. A couple of the links with plans are probably dead, but THIS link about bird houses sizing still works.
The people have spoken and the Fat Bear has sung: we have a winner of the 2021 Fat Bear Contest. And it happens to be my favorite of the final pair: Otis (bear #480). See below, and look at that weight gain on Otis in less than two months!
If you read their biographies, you’ll see that Otis was at a physical disadvantage here. He’s a Senior Bear, about twenty-five years old. Walker, in contrast, is a spry youngster of fourteen. Further, as you can see in the photo below, Otis has dental issues. As the bio states:
As bears age, they experience a variety of challenges and Otis is no exception. In particular, he is missing two canine teeth and many of his other teeth are greatly worn. Otis must also compete with younger and larger bears who want access to his fishing spots. Otis is more likely to be displaced by these bears than he is to displace them.
That’s one seriously messed up set of choppers! So, as the disadvantage Underbear, Otis got my vote, and won handily, by nearly 6,400 votes. Sadly, I don’t think the bears get a prize from the Park Service for winning: their reward is fitness coming from fatness: they have a higher chancing of surviving the winter hibernation.
So congratulations to Otis, and let’s hope he’s back next year. As the National Wildlife Federation notes, most grizzlies are dead by the time they’re twenty-five.
Today begins a series of excellent photos of tree swallows tending their broods, which will be posted from time to time; they were taken by Emilio d’Alise, whose notes and IDs are indented. Click on the photos to enlarge them.
Nest Competition and Feeding
From 2007 to 2013, I lived in Colorado and worked in Woodland Park (8,100 ft. elevation). We had an empty lot next to the office, and we put up a Bluebird house. For the first three years, we had Bluebirds nesting in it, but in 2011, a pair of Tree Swallows (Tachycineta bicolor) moved in, and returned each year for the next three years. This post from 2011 documents the final weeks before that year’s brood fledged — they all fledged, but a hawk got one of them —and it includes photos and videos.
But, the year that I got serious about photographing them was 2012, and these are some of the photos from those sessions.
As I mentioned, the birdhouse is sized for Bluebirds, which are smaller birds, so the typical Tree Swallows brood of 5-7 makes for a pretty tight fit just before they fledge. Early on, the adults will enter the nest to feed the chicks.
Nest Entry to Feed
Nest Competition
Once large enough, the chicks fight for position at the entrance. This sequence of photos — again, from 2012 — shows one bird displacing another at the entrance and scoring a tasty bug (at least I assume it’s tasty to them).
I’m breaking precedent by putting up two successive posts by one person becaue Tara Tanaka’s new video, filmed four years ago but posted only yesterday, was so charming and amazing, and it shows LOTS OF DUCKS! Thousands of them, all on the wing together, and of three species! The mallards, of course, are my favorite (Tara said she put in extra shots of mallards for me). With such a density of flying ducks, I wonder how they manage to avoid collisions in the air. Also, it looks as if they fly segregated by sex, but that may simply be because the drakes are more conspicuous.
Here are Tara’s notes. Be sure to enlarge the video by clicking on the four outward-facing arrows, and put the sound up, as there’s lovely music. Don’t miss this one!
2021-09 Bosque Blast-offs: Pintails, Mallards, Widgen and Shovelers
This was one of the most spectacular wildlife scenes that I’ve ever witnessed. I shot the footage for this video in 2017 at Bosque del Apache NWR, and have been thinking about creating it for four (!) years. It was time.
The experience of watching that many ducks lift off was indescribable, but the music that I chose does the best job of conveying the emotion I felt that can be shared through video.
It’s that time of year when the Alaska peninsular brown bears (Ursus arctos), a population of the grizzly bear, are fattening themselves up on spawning salmon to lay on the fat for winter hibernation. As Wikipedia explains:
Brown bears on the Alaska Peninsula usually feed on spawning salmon, and use many different ways to catch them. These include waiting at the bottom of the falls for the fish to jump, or standing at the top of the falls waiting to catch the fish in midair (sometimes in their mouths). Bears also have much experience at chasing fish around and pinning the slippery animals with their claws. After the salmon runs, berries and grass make the mainstay of the bears’ diets, after which they put on sufficient fat reserves and go into hibernation
You can see them hunting on this live bear cam at the classic site of Brooks Falls in Katmai National Park in Alaska. Someday I will go there to see this amazing spectacle for myself!
But for our purposes it is (click on screenshot). . . . . . wait for it. . . . .
It starts tomorrow and extends through October 5. The goal is to choose the bear who has gotten the fattest on salmon, and you do this by voting for one bear out of each pair per day. You vote for the fatter one, and that’s put up against another porker on the next day. At the end of the week, the Fattest Bear is crowned. (And remember, the more fat, the more likely you are to get through hibernation in good condition, so FATNESS IS FITNESS!)
Go to the link [it will be the “vote” button on the page above], start voting tomorrow, and follow these instructions:
Download your blank bracket. Fat Bear Week is from September 29th to October 5th, your vote decides who is the fattest of the fat. Matchups will be open for voting between 12 – 9 p.m. Eastern (9 a.m. – 6 p.m. Pacific). Click the bear you would like to vote for. That bear will then be outlined in blue. Then enter your email in the space and hit enter. You know that you have successfully voted if you see the total votes for each bear.
Click to enlarge and see the contenders. You can get more information at the “Meet the Bears” site here. There’s also a junior bear contest for the young ‘uns, but you can suss that out for yourself. Remember: it’s Survival of the Fattest! Here are the brackets so far:
I’m partial to “Chunk”, as he looks as if he’s prone to getting in scraps. He’s HUGE!
Chunk (Bear 32) is a large adult male with narrowly-set eyes, a prominent brow ridge, and a distinctive scar across his muzzle. Even at his leanest, Chunk carries substantial fat reserves, especially on his hind quarters. In early summer he tends to shed much of the fur around his shoulders and neck. This gives him a two-toned appearance and exposes numerous scars and wounds. By late summer, his newly grown fur is dark brown.
Biography
Chunk was first identified in 2007 as an independent, chunky-looking two and half year-old bear. Since then, he’s grown to become one of the largest adults at Brooks River. He was estimated to weigh more than 1,200 pounds (544 kg) in September 2020.
Chunk ranks among the most dominant bears at Brooks River. This allows him greater access to mating opportunities and fishing spots. Like most large bears, Chunk is not hesitant to challenge and displace others from the resources he wants. However, his behavior can also be enigmatic. He may wait patiently to scavenge leftover salmon and even play with other bears. These are two uncommon behaviors for a dominant bear to display. Due to his size and strength, Chunk is poised to take advantage of opportunities not available to most other bears. Yet, it is only by observing his full range of behaviors that we can get a true sense of his individuality.
Look how fat he’s getting:
There’s a Hall of Champions of the Pudgiest Bears for each year since 2014. Meet last year’s champion, a male named “747”. Look at the belly on that porker!
So start voting tomorrow (you must enter your email address). Good luck to all ursines, and may the fattest bear win. (They don’t weigh them; victory is determined by our looking at before and after pictures.)
Meerkats (Suricata suricatta) are a type of social mongoose that lives at the very southern part of Africa. We all know them and love them because they’re cute and they stand on their rear legs when surveying their surroundings for danger. The BBC’s Planet Earth has filmed them so extensively that they’ve become inured to the presence of humans, and even stand on photographers’ bodies and heads.
Here’s an adorable and short BBC video showing this behavior. Look for a quip about the size of the director’s buttocks!
We’re running uncomfortably low on wildlife photos, so if you have some good ones, please send them in!
Today’s photos are a series from Susan Harrison, a professor of ecology from UC Davis who has contributed once before. She portrays the many ways birds cope with extreme heat. Susan’s notes are indented, and you can enlarge the photos by clicking on them.
BIRDS IN HOT WEATHER
Spring and summer 2021 provided all too many opportunities to observe the ways birds cope with hot weather. Most of the pictures below were taken on days that reached the mid-30’s Celsius (mid-90’s Fahrenheit). The birds seemed to be doing fine, but who knows what future years will bring.
PANTING. These birds at Falcon State Park, Texas, in April look like they were calling or singing but they were actually panting.
GULAR FLUTTERING: An enhanced form of panting, found in some birds with throat pouches, seen here at Edinburg Wetlands Park, Texas, in April. [JAC: Mallards do this.]
RESTING IN THE SHADE: These two large raptors were hanging out not far from each other along Putah Creek in May. Maybe it was too hot for songbirds to bother mobbing them?
SHADING THE NEST: Herons are known to use their wings to shade chicks in the nest. Four weeks after this photo was taken in Ashland, Oregon in May, temperatures reached 24 degrees Celsius above the long-term mean June high. I wasn’t around to see if these parents spread wings over their four young. Next time I’ll brave the heat and look.
FORAGING EARLY IN THE DAY: This species is an alpine specialist that forages around snowfields in summer. On a peak above Crater Lake, Oregon, on a day that hit 20 degrees Celsius above the long-term mean July high, I saw them active only before 8:00 am. The last small patches of snow largely disappeared that day. Will this species be the bird equivalent of pikas, with nowhere to go in a warmer climate?
I couldn’t resist watching this to the end, but it’s only 4 minutes long. My main question was “will they eat ALL the cheesecake”? I’ll leave it to you to find out. If you’re an expert on pismires, tell us what species this is.
The destruction stops at 3:19 (102 hours) and then they reverse the film. I thought they’d take every crumb! They certainly weren’t Jewish ants. . . .
And that cheesecake looks pretty wonky. It looks more like cake than cheesecake.
