Nuthatch & Friends

The nuthatch (Sitta carolinensis) has a lot of friends. It often teams up with chickadees and titmice. While larger flocks give greater protection from predators, more species diversity within the flock improves problem solving (1). Birds in diverse groups were able to get food from a new feeder faster.

1. Freeberg, T.M., S.K. Eppert, K.E. Sieving, and J.R. Lucas. 2017. Diversity in mixed species groups improves success in a novel feeder test in a wild songbird community. Scientific Reports. Volume 7, Article number: 43014.

Protective Nests

Birds nest in trees, on the ground, on water, among cliffs, and in caves. They build their nurseries from plant materials, mud, dung, saliva, spider silk, pebbles, and animal hair. Some nests have roofs or multiple rooms. Some are simple scraped depressions in the earth or natural cavities in trees.

Most songbirds construct cup-shaped nests which require about 1000 trips to bring in building materials (1). The birds use their feet to scrape, chests to push, and beaks to manipulate twigs and grasses as they rotate. Exhausting! Why go to such an extreme effort? Predators. Birds living on predator-free islands nest on the ground.

Some ground-nesting birds have other ways of avoiding predators… like teaming up with defenders. The red-breasted goose of Siberia nests next to peregrine falcons. The geese act as look-outs for foxes; the falcons attack. Some birds build their nests in ant or termite colonies to protect the eggs.

These sleeping bird babies, pictured, are cardinals. Their parents built this camouflaged nest in the crook of a pear tree. If dad hadn’t stopped by with some breakfast, I would have never realized they were there.

1. Collias, N.E. 1964. The Evolution of Nests and Nest Building in Birds. American Zoologist. 4: 175-190.

Hole-y Eggs

The hard shell of an egg may seem like a thin yet impenetrable fortress. At the microscopic level, though, it’s more like a colander. Thousands of pores allow oxygen into the egg (and carbon dioxide out) so the developing embryo won’t suffocate.

Those pores could potentially allow bacteria into the egg. In most birds, though, a thin layer of protein called the cuticle (or bloom) is added to the outside of the shell just before it’s laid. That layer blocks bacteria from moving inside the egg. Considering that eggs and waste products all pass through the same opening in birds, that cuticle can be extremely valuable. If you’re looking for the cuticle on eggs you bought at the grocery store, you won’t find it. Eggs here in the U.S. are washed before heading to market. The process is surprisingly complex since washing eggs improperly can cause bacteria to enter through those pores. It’s also the reason you’ll find eggs in the refrigerated section. In Europe, the cuticle stays on and eggs are sold at room temperature.

Our understanding of eggshell microstructure impacts Canada Goose populations. The process of “addling” by wildlife management professionals controls the population size of the birds. A thin layer of oil is rubbed on the outside of the eggshell, cutting off the oxygen supply for developing goose. The parents, who see a whole nest full of eggs, stop laying more. But only the un-oiled offspring will survive to hatch. [FYI: it is illegal to do this without a permit – see the Migratory Bird Treaty Act of 1918.]

Dinosaur eggs had pores too, and the structure and placement of those pores tell paleontologists a thing or two about how dinosaurs lived. For instance, some dinosaurs laid eggs in an exposed nest while some buried their eggs. Exposed eggs generally have fewer pores than the buried ones since gas exchange proves more difficult underground. Fewer pores are also found in eggs laid in dry environments to limit water loss. The Museum of Paleontology at Berkley has an excellent site with more information about dinosaur eggs.

Real Monsters – The Cockatrice

In medieval bestiaries, entries portrayed the cockatrice as a rooster with the tail of a snake. It’s said to hatch from the egg of a cockerel that’s been brooded by a snake or toad. Often interchanged with the basilisk, only a weasel (or Harry Potter) can kill it.

Wow. Crazy, right?  Maybe not so much.

Could poultry grow a snake-ish tail? Considering the evolutionary history of birds and embryonic development, yes. Birds are the last surviving descendants of dinosaurs, and early birds (evolutionarily speaking, not the worm-getting kind) had long tails. Over time, shorter-tailed members of the group prevailed as they flew unimpeded, and with better control, among brush and between branches. Vertebrae that once grew, fused as random genetic mutations delivered more successful flight. Genetically, just a few genes (possibly just one), activated early in development, control vertebral growth and tail elongation (1). So if you can stop that gene from turning on, you might just get a tail.

The second aspect of the cockatrice/basilisk story involved being born from a rooster’s egg. Now, that can’t be true – only hens lay eggs. Well, just like in humans, sex can be confusing. Primary sexual characteristics include sexual organs. In order to lay an egg, the bird would need an ovary. But most people identify hens and roosters by secondary sexual characteristics like coloration, size, and the presence of a comb and wattle. These traits develop because of hormones. If a female bird receives a dose of male hormone, she can produce rooster-like traits. This situation is actually not so rare. Because birds only use one gonad, a disease on the ovary would cause the other to develop. Since testes and ovaries develop from the same structure, the hen could get a dose of male hormone, producing rooster-like traits, and still lay an egg (2).

Brooding by a snake or toad wouldn’t help a chicken egg hatch. However, it’s not unusual to find a snake in a nest. Snakes of course eat eggs, and some birds even use snakes as partners to protect their nests from parasites or rodents.

As for death-by-weasel, the cockatrice/basilisk story is probably getting mixed with a cobra (3). The mongoose, which looks similar to a weasel, has an amazing cellular adaptation that makes them resistant to cobra venom. Many Greek and Egyptian stories (as well as the modern tale of Rikki-Tikki-Tavi) glorify the snake-killing abilities of the mongoose.

So next time you hear of a mystical beast that couldn’t possibly be real, give it a chance. And if you’d like to read more about the cockatrice and its devilish ties, visit awingandaway.

 

1. Rashid DJ, Chapman SC, Larsson HCE, Organ CL, Bebin A-G, Merzdorf CS, Bradley R, and Horner JR 2014. From dinosaurs to birds: a tail of evolution. EvoDevo 2(25)
2. Jacob J and Mather FB. 2000. Sex reversal in chickens. UFL-IFAS. FactSheet PS-53. http://ufdc.ufl.edu/IR00003037/00001
3. Alexander, RM 1963. The evolution of the basilisk. Greece & Rome. 10(2) 170-181.

Purring Predators

As agriculture took hold in Middle Eastern societies about 10,000 years ago, archeological evidence of cat domestication appears. When humans began storing grain, any rodent-killing animal was a benefit. But the presence of cats didn’t spread along with agriculture. Egyptians may have revered cats, but other civilizations used weasels or snakes to limit mice. In the painting “Lady with an Ermine” by Leonardo da Vinci, the weasel may symbolize purity or the young woman’s last name (similar to the Greek word for ermine). With all due respect, however, I think the animal may have just been the lady’s pet; weasels were more common pets than cats at that time.

Cats may have been popular in Egypt during the heyday of the Roman Empire, but Greeks and Romans kept weasels as their rodent-killing pets. Cats joined European families around the fourth century but were relatively uncommon until the 1600s (1).

Nowadays, of course, cats are popular pets and internet memes. Their omnipresence is also a major cause of concern to ecologists and bird lovers. In a 2013 research article, Loss et al. estimated our purring pets (and their feral cousins) kill about 2.5 billion birds and 12 billion rodents each year in the U.S. alone (2).

P.s. The adorable cat who posed for this painting is our own 18-year old feline princess, Flea. She’s killed exactly one bird in her life, a fledgling finch who accidentally flew into her mouth. Flea didn’t even bite down; the little bird panicked to death.

1. The Oxford Handbook of Animals in Classical Thought and Life. G.L. Campbell. 2014. Oxford University Press.
2. Loss, S.R. et al. 2013. The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications 4:1396.

Sometimes you DO choose your family (of geese)

What would happen if an adorable 3-day old gosling was placed between two wire enclosures, one containing a sibling, and one containing a same-age gosling from another clutch? Would the baby bird recognize its brother or sister and patter over to its relative?

The answer: yes… at least as often as dentists recommend sugarless gum*. In four out of five trials, the little puffball sidled up to its sibling rather than a stranger’s young’un.

There’s one catch. The youngest goslings (ages 3–9 days) prefer groups. Even if it’s a group of unfamiliar goslings, the little bird almost always waddled over to an unknown group rather than a single relative. By 15 days old though, the youngsters reliably reunite with their kin, no matter how small their family.

p.s. I created this image at an awesome carbon dust workshop, coordinated by GNSI-Carolinas, this weekend. Marlene Hill Donnelly from the Chicago Field Museum was our fearless instructor – she’s wonderful!

*Radesäter, T. 1976. Individual sibling recognition in juvenile Canada geese (Branta canadensis). Canadian Journal of Zoology, 54(7): 1069–1072

Signs of Spring: Robins and Lawn Mowers

Two robins (Turdus migratorius) hopped through the yard this week – spring is on its way. The sound of lawn mowers now drift through the air, confirming the avian prediction. Shockingly, these two very distinct signs of warming weather are actually related, according to a backyard research study conducted in 1979.

L.A. Eiserer conducted a series of scientific (well, somewhat) studies examining the impacts of lawn mowing on robin-hunting behaviors. Robins spend more time foraging when grass is short, especially just after it has been mowed.

So is it the mowing or the height of the grass that impacts robin behavior? Eiserer mowed his lawn to two different heights, 2.5 and 4.5 inches. (I wonder if his neighbors complained.) The robins spent 10x as much time in the shorter patch. Apparently, the birds eat different foods when exposed to different heights of grasses. In short grass, robins go for worms; in longer grass, they pluck small insects off the blades. The short-grassed hunting grounds may just be more efficient for finding a heartier meal.

But that doesn’t discount the act of mowing. Observations over the same time of day show the birds prefer hunting in a freshly mowed yard rather than the day after. No difference in grass height, but perhaps the act of mowing disturbs invertebrates, allowing for a more successful hunt.

Overall, I miss the days when a researcher could sit on a suburban porch and time how long a couple of robins spend looking for food. As I struggle to teach my students how to think like scientists, reading a study like this makes me long for the good old days.

 

Eiserer, L.A. 1980. Effects of Grass Length and Mowing on Foraging Behavior of the American Robin. The Auk. 97(3) 576-580.

Snowbird Shape-shifters

Those small slate-and-white sparrows hopping across the frozen ground are true snowbirds. They spend summer in Canada and move south to the U.S. during the winter. Some, like their human counterparts, even migrate to Florida.

In the late 1800s, R.W. Shufeldt wrote of two birds called “snowbirds.” One medium-sized bird, the Snow Bunting, became known as the “snowflake.” The smaller bird, the Dark-eyed Junco, was unequivocally called the “snowbird.” Shufeldt expressed his displeasure at the bird’s new moniker “junco” – he tried to determine, unsuccessfully, the etymology of the word (it means “reeds or rushes”) since the Dark-eyed Junco does not live among reeds or rushes.

Shufeldt’s article also referenced Alexander Wilson’s description of Junco folklore. New Englanders told Wilson that Dark-eyed Juncos change their plumage to become the Chipping Sparrows of summer. Before you laugh (or after you’re through), many birds significantly alter their plumage during the breeding season… although the Dark-eyed Junco does not. These two birds are both sparrows, trill similar songs, and feed on the ground.

While Dark-eyed Juncos do not morph into Chipping Sparrows, they have their own form of transmutation. Those round balls of bird aren’t fat, they’re fluffy. Feathers trap air, an excellent insulator. The birds puff up their feathers, a downy winter coat, keeping them toasty warm.

p.s. Red and the Peanut wrote a great post about the name “snowbird.” I recommend it!

Going Nuts for Blue Jays

Watch out, squirrel. You’ve got competition this autumn.

Acorn gathering and burying is often considered a squirrel hobby. Turns out, Blue Jays (Cyanocitta cristata) are pretty good at it too. Okay, really good.

Blue Jays have a pouch in their throat they can use to hold acorns (up to 5!). When they reach a caching site, the birds will spit up the acorns and bury them one at a time under leaves or in the dirt.

One study showed that Blue Jays were responsible for relocating more than half the acorns in a forested plot. (1) That’s over 130,000 acorns! And yes, the birds usually remember where they’re hidden. They’ll often place the morsels near “beacons” like rocks or fences.

Another study suggested that the birds were the most likely culprit in the spread of oaks after the last Ice Age (2). Most trees with heavy seeds returned slowly to the barren lands left when the glaciers retreated. But the oaks came back quickly. Squirrels couldn’t do that, but Blue Jays could.

1. Darley-Hill S and Johnson WC. 1981. Acorn dispersal by the blue jay. Oecologia. 50(2) 231-232.
2. Carter JW and Adkisson CS. 1986. Airlifting the oaks. Natural History. 95(10) 40-48.

By the way, Lego(R) came out with a bird series this year – and it includes the blue jay. They should add a small Lego acorn to go along with it.

Invasion of the House Finch

Once upon a time, House Finches (Haemorhous mexicanus) only lived west of the Rocky Mountains. Then, in 1940, a group of captive birds flew to freedom from their New York cages. Their numbers slowly grew until… BOOM… population explosion. Today, House Finches reside throughout the U.S. and Mexico.

There’s a downside to dense populations though – disease. In the 1990s, a bacterium (Mycoplasma gallisepticum) started swirling among groups of House Finches. The infection causes conjunctivitis (like “pinkeye”) in the birds. If you’re a bird with swollen eyelids and crusty build up, you’re not going to be very good at flying or avoiding the neighbor’s cat.

Today, roughly half as many House Finches live in the East compared to 20 years ago.

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If you’d like to learn more about House Finch diseases (with gross pictures), visit http://www.birds.cornell.edu/hofi/abtdisease.html.

And if you’d like to see the growth and decline of House Finch populations in your state, check out www.pwrc.usgs.gov/BBS/RawData/ (1)- fun with data!.

1. Pardieck, K.L., D.J. Ziolkowski Jr., M.-A.R. Hudson. 2014. North American Breeding Bird Survey Dataset 1966 – 2013, version 2013.0. U.S. Geological Survey, Patuxent Wildlife Research Center.