Adapted from Jim Conrad's online book A Birding Trip through Mexico, This excerpt from "Laguna Catemaco" in southern coastal Veracruz state
For every 20 coots out there maybe there's one Pied-billed Grebe. Though these two species share the lake's surface they're clearly foraging for different foods, and thus their niches are not overlapping. In fact, coots mainly eat aquatic vegetation, while grebes are almost entirely carnivorous, mainly eating crustaceans such as crayfish, as well as small fish, mollusks, and aquatic insects.
When coots dive they soon bob back to the surface near where they disappeared but grebes remain submerged for 45 seconds and longer, usually resurfacing surprisingly far from where they dove.
Though the coot's food obviously has much less nutritional value than the grebe's high-energy carnivorous diet, my impression is that the coots spend less time feeding than do the grebes As I scan Lake Catemaco's surface, every Pied-billed Grebe seems hard at work alternating long dives with brief periods of catching breath, while a large percentage of the coots are bathing, standing on Water Hyacinth rafts sunning themselves, or just idly floating, looking around.
A Pied-billed Grebe pops to the surface and as it catches its breath a Green Heron comes flying very low over the water with its legs stretched forward, giving the appearance of being about to land atop the grebe. Neither I nor the grebe can imagine what's on the heron's mind. The grebe submerges just long enough for the heron to pass, then surfaces again, looks over its back, and I swear there's an expression in its face, saying, "You fool!"
And how exquisitely grebes are adapted for their life in water. As with coots, their toes are "lobed" with a series of flaps, so as they push their feet backward against the water the flaps open up like oars, propelling the bird forward. Then when the feet are drawn forward the flaps collapse and the water offers little resistance. Grebe's toenails are even flattened, like little paddles, something very rare among birds.
Moreover, a grebe's legs arise far back along its body. This makes it hard for grebes to move on land but, in accordance with the laws of physics, it enables the birds to harness a powerful forward thrust when diving. Like many birds highly adapted to diving, grebes have difficulty lifting themselves from the water's surface. With rapidly beating wings they taxi across the surface with their running legs frantically providing extra propulsion below them, before becoming airborne.