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Egg Coloration

2013 April 22
by Seth Inman

Gray Catbird nest with eggs. Photo by Flickr user JMK Birder.

In my last post I covered Killdeer eggs and nests, focusing on their pyriform shape and mottled coloration. Here I’d like to talk a bit about egg pigmentation in more detail, since variation in patterns and colors is so fascinating in itself!

We saw with Killdeer that the spotted coloration of the eggs helped them blend in better with their surroundings, but what about eggs that aren’t marked at all? Well, white eggs, as we might assume, don’t have much camouflage potential unless placed in a white background, which is essentially limited to very light sand or gravel. White eggs, therefore, need to be disguised in other ways. They can be covered by things like feathers or vegetation, which is what many waterbirds do–wet leaves or seaweed can even stain parts of the eggs brown! They can also be laid in burrows or cavities where they won’t be seen anyway, which is what many woodpeckers, parrots, and owls, among other species, do.

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Focal Species Close-up: Killdeer

2013 April 19
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by Seth Inman

Photo of Killdeer in Upper Newport Bay Nature Preserve by Morgan Terrinoni

Unlike the rest of shorebirds in the family of plovers, dotterels, and lapwings, Killdeer inhabit places other than the beach. Why? In part this is because they enjoy expanses of gravelly rocks and short grass, and there is only so much coastline. With all the parking lots, golf courses, well-maintained lawns, grazed pastures, and athletic fields in the US alone, it isn’t surprising that they took to the niches that were much more open to a ground-dwelling bird than the fairly packed shores. The fact that Killdeer have chosen homes that quite often happen to be in (sub)urban areas points to the relative comfort the species has for human proximity, and to a degree explains their successful expansion throughout North America as year-round residents.

In the grand scheme of things, we can outline three reasons Killdeer choose a certain habitat: best availability of prey, best protection from predators, and best chances for survival of offspring. My focus in this post is on the last factor as it relates to Killdeer nests and eggs.

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Silky Nests in Funky Places

2013 April 15
by Seth Inman

Photo by Charles Spencer, AZ

If you’ve ever watched a hummingbird for some time, you’ve probably thought that they’re one of the cutest and most exciting birds that you can find in your yard. Most would agree that it is some combination of their size, speed, vibrancy (of both color and motion), and relative rarity that can make them so appealing to us, but have you ever seen hummingbird nestlings? Or a nest, for that matter?

In the past couple years of the Funky Nests in Funky Places competition we’ve received photos of over a dozen hummingbird nests, all but one of which have been built on a man-made object! Seeing the hummingbird hatchlings poke their little beaks out of the tiny cup that the mother has created for them is a wonderful experience, and the feat of each minuscule nests’ construction becomes more impressive when you consider what the assembly materials are.

As you take a close look at the contributors’ photos shared here, you should be able to see (despite occasional blurriness) that the majority of the nest cup seems to be comprised of a silky substance. Surprisingly enough, much of this is spider web! Also known as spider silk, these strands of what humans normally think of as a fragile material (though some species of spiders produce silk with a higher tensile strength than steel) are perfect for hummingbirds’ purposes because they are sticky, light, stretchy, and strong. read more…