Eared Grebe - Podiceps nigricollis

Right now (October 7, 2014) Eared Grebes are present in pretty good numbers, so I couldn't resist taking some shots of this one as it navigated around the Canada Geese and dabbling ducks at Las Gallinas ponds. When I got home I realized that the shots were interesting shots, as the 2 photos, taken 6 seconds apart, show how the features of a bird change with posture and activity.

First shot is a typical Eared Grebe posture, with a steeply sloped forehead, a peak of the crown above the eye, and the high-riding stern. 

Soon thereafter it began to swim faster, anticipating a dive, and the feathers became more streamlined. The forehead slope is now more shallow, like a Horned Grebe's, the peak of the crown a bit behind the eye, and the butt end is sleeker and low-riding.

I think this is young bird, molting into its "first basic" plumage. Note the amber/orange iris, as opposed to the redder iris characteristic of the adult Eared Grebe. The typical "first fall" birds are browner, but I imagine there is a fair amount of variation.

Eared Grebe - Podiceps nigricollis

Lots of Eared Grebes right now at the Las Gallinas ponds right now, most of them busy feeding on insects at the water's surface, almost like phalaropes. This shot shows an eye that is more orange than red, perhaps indicating a sub-adult. 

Next shot is a crop to show eye and bill better. Juvenile Eared Grebes have a tan or brown-orange iris, and adults a brighter red. The BNA account (#433) has one photo of similar bird, with a similar eye.The grebe here is not in full basic plumage, as the neck still looks pretty dark, but the dingy neck appearance helps separate it from the similar Eared Grebe, which has a whiter neck in winter. Right now most of the birds are in transition, so it can be confusing. But note the steep forehead with the peak above the eye, definitely "eared". The bill looks more Eared than Horned, but it's not as flat on top as on the average Eared Grebe.

This shot of a juvenile Eared Grebe, taken a few years ago at Bodega Bay, shows the lighter iris and a wash of brown on the grays of the head and back.

Eared Grebes are said to be the most numerous of all grebe species in the world, with a North America population of something like 4 million. They love saline lakes, and stage in huge numbers at the Great Salt Lake and Mono Lake (September to Dec). When gorging on brine shrimp and brine flies at staging areas they are flightless (see below).

I found the account in Birds of North America Online, #433, by Cullen et. al. to be of particular interest in regard to the longs periods of flightlessness in this species, and the dramatic fluctuations in the birds weight and organ sizes, to whit:

"While at fall molting/staging lakes, adults more than double their arrival mass and allow the pectoral muscles to atrophy below a size that allows flight. Then, during a hyperphagic period, they greatly increase the size of the organs involved in digestion and food storage. These changes in size and proportions—the most extreme yet known for any bird—are then reversed during a brief predeparture period, when the birds catabolize much of their just-deposited fat, increase heart size, and reduce digestive organ mass to perhaps 25% of peak in preparation for a nonstop flight to wintering areas. The function of the predeparture events is to reduce wing-loading while maximizing flight range and performance. Migration occurs shortly after food supplies run out, typically in December–January. As a result, the Eared Grebe is the latest of the North American migrants to move to its winter stations. Because a similar atrophy/hypertrophy cycle is repeated 3–6 times each year, the Eared Grebe has the longest flightless period of any volant bird in the world, perhaps totaling 9–10 months over the course of a year. At fall staging areas alone, flightless periods average 3–4 months for adults and may reach 8 months or more in nonbreeders."     (volant = "flying", or capable of flying or gliding)

For an excellent article on sorting out confusing fall Podiceps grebes see:  

Kaufman, K. 1992. The practiced eye: Identifying monochrome Eared Grebes. Am. Birds 46:1187-1190.