Today we have another science-and-photo feature by Bruce Lyon, a professor of ecology and evolutionary biology at the University of California at Santa Cruz. This time the subject is not coots but grebes. (Baby grebes are about the cutest waterfowl going.) Bruce’s notes are indented, and the photos are great!
The wetlands where we study American coots in central British Columbia, Canada are also packed with lots of other species of waterbirds. The bird densities are very high, which makes the wetlands feel incredibly birdy and active. The floating blinds we use in our coot study are also great for getting up close and personal with these other water birds—a bird photographer’s dream. Today I will highlight the grebes that nest on our study wetlands.
Below: Eared Grebes (Podiceps nigricollis) are gorgeous birds with their yellow ear tufts and bright red eyes. This species also breeds in Eurasia, where it is known as the Black-necked Grebe. They nest in colonies ranging from a dozen to up to hundreds of pairs, and nests are often very close to each other—1 or 2 meters. The photo below shows a nest in low density colony where the birds were spread out. The nests are floating platforms of wet vegetation. Whenever the birds leave the nest they hide their eggs by covering them with the nest material. The pink flowers in the photo are aquatic smartweed (or knotweed) flowers in the buckwheat family (Polygonacea).
Below: When the eggs hatch, the entire grebe family leaves the nesting colony and the chicks are ferried around on their parents’ back like royalty. The family does not return to the nesting area but instead roams widely on the wetland. Baby grebes have striking plumage patterns and are apparently called ‘stripe-heads’. In addition to the stripy plumage, the chicks have bare patches of skin that can rapidly change from a pale flesh to a bright red color. The function of the plumage markings is not entirely clear, but in some species the bare patches seem to function both for begging for food and in signaling distress. When the chicks are hungry the patches are dull, and when they are not hungry they are bright red. Perhaps the skin patches provide an honest signal of chick hunger that lets the parents assess which chicks need the food the most.
Below: Typically one parent searches for food and brings it back to the floating restaurant.
Below: Another portrait of a parent carrying its chicks. Why grebes (and other birds like loons and some swans) carry their chicks is not entirely clear. I am currently working on a short note about the topic for a scientific journal. Some of the potential benefits of carrying chicks include: (1) brooding the chicks to keep them warm (the small–bodied chicks would loose a lot of heat if they were to swim on their own); (2) safety from predators (our wetlands lack predatory fish but carrying chicks might make them safer from aerial bird predators) and, finally, (3) carrying the chicks might allow the family to travel greater distances than would otherwise be possible (although ducks do not carry their kids and broods, some species seem to be able to travel pretty big distances—not Jerry’s ducks though!)
Below: A gorgeous Horned Grebe (Podiceps auritus). I only ever found one nesting pair of these birds at my study site—on a small isolated pond. Horned Grebes are very different from Eared Grebes in that they are fiercely territorial—only one pair per small wetland.
Below: The small wetland where I found the Horned Grebes.
Below: Another view of the Horned Grebe.
Below: The pair was busy building a nest while I watched them. They were fetching old reed stems as building material and often swam under water with the material. Grebes are excellent swimmers: they are foot-propelled divers and, like coots, have lobed rather than webbed feet. The feet are located very far back on the body, which is great for swimming but it sucks for walking: these birds can barely walk on land and even getting up on their nests seems like an ordeal.
Below: Red-necked Grebes (Podiceps grisegena) also nest on some of our wetlands. They too are territorial so we never get more than one pair per wetland. This species is also considerably larger than the other two species described above.
Below: Up periscope—a little stripe-head backrider sticks its head up to get a view. Dad, are we there yet?
Below: Both parents are carrying chicks so I guess they were taking a break from feeding. Note that both parents have the same colorful plumage—this pattern, and grebes specifically, played an important role in a big debate in evolutionary biology in the 1930s. Grebes (and many other birds) are interesting because they have dull winter plumage but both sexes then molt into a colorful garb for the breeding season. Julian Huxley, an evolutionary biologist famous for his role in the Modern Evolutionary Synthesis, studied courtship in Great Crested Grebes in Europe and came to the conclusion that sexual selection by mate choice could not explain the courtship and plumage patterns of grebes, or any organism for that matter. Darwin had proposed a mechanism of sexual selection that could explain ornamentation of both males and females—mutual mate choice by both sexes—but he then quickly ruled out the idea because he thought males were too randy to be picky about mates. It turns out that Darwin got this one wrong and sexual selection through mutual mate choice has now been clearly documented in lots of birds. This mechanism may explain the brightly colored males and females in grebes. Darwin was wrong on a minor point (mutual sexual selection) while Huxley was profoundly wrong on a key point (sexual selection by mate choice). Nonetheless, because he was such an influential figure, Huxley’s views pretty much stifled interest in sexual selection for some time.
Below: One parent offers food (a dragonfly larvae I think) while the other shakes a caddisfly larva to remove the protective house the larva has constructed around itself (the water flecks are from the shaken caddisfly). Caddisfly larvae are preferred prey items for both coots and grebes and it is easy to see when one has been captured because the birds have to vigorously shake the houses to extract the larva within.
Below: A caddisfly larva in its house (photo from the web).