If you haven’t heard of CUBs–Celebrate Urban Birds–yet, click here. 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.
The first thing you might notice from the photo above is how well-camouflaged the spotted eggs in the gravel are. As you can see from these Semipalmated Plover, Ringed Plover, and Black Oystercatcher eggs, several other shorebirds share this trait: eggs are a light sandy color and splotched all over with brown spots of varying darkness.
The next think you’ll notice about Killdeer eggs, this time from the gallery above, is that their shape is quite different from, say, an Eastern Bluebirds‘ or Barn Swallows‘ eggs. The technical term for this type of egg is pyriform (i.e. pear-shaped), and, as we saw with the coloration patterns earlier (the Ringed Plover eggs in particular), many shorebirds share this shape trait. For plovers’ purposes, since most have four eggs in the nest at a time, orienting the four eggs with their small ends pointing inwards helps them fit closer together for incubation, and the tight pack of mottled ovals looks more like a group of pebbles.
An argument advanced for other species with pyriform eggs, such as murres, is that their long uneven shape makes them roll in circles rather than in a straight line. So for cliff-nesting species like murres, the benefit of pyriformity is that a disturbed egg will hopefully roll in a tight circle instead of off the cliff. Since Killdeer nests are typically a simple scrape in the substrate (gravel, pebbles, dirt, sand, sparse grass, or a mix of them all) to which other materials (such as rocks, sticks, and shells) are added only after the eggs have been laid, perhaps Killdeer eggs’ pyriformity helps when the parents choose to nest on gravelly roofs!
Now that we’ve reached the starting date for the Funky Nests in Funky Places competition, look around your neighborhood’s grassy and gravelly areas. Although you might not see Killdeer right away due to their own fairly good camouflage, if there are any around you should be able to hear their sharp kill-deer call, and if you get too close to their nest you might witness their broken-wing display. Put these two traits together and you’ll always remember the species’ scientific name: Charadrius vociferus — vociferous birds who put on charades!