Eared Grebes are flightless for up to nine or ten months each year—the longest known flightless period for any bird species capable of flight worldwide.
While staging at Great Basin saline lakes for three to four months during the fall, the birds molt their wing feathers and rework their bodies so that digestive organs and leg muscles become larger and flight muscles smaller. They drastically increase their body fat by feeding on abundant brine shrimp and brine flies. Then, as late fall or early winter approaches, the Grebes reinvest in flight muscles, reduce non-flight muscles and organs, trim some body fat, and move on to their southern wintering grounds.
From a conservation perspective, this flightless period at fall staging areas is a critical point of vulnerability, in addition to their reliance on a few key lakes. About 99 percent of North American Eared Grebes stage at either Mono Lake in California or Great Salt Lake in Utah. Oregon’s Lake Abert is also used but to a lesser degree. Prior to becoming flightless, the Grebes have the ability to choose among locations, but after becoming flightless, the grebes have no flexibility to respond to deteriorating habitat conditions. Limiting habitat conditions during this flightless period can have carryover impacts in future years. For example, Belovsky et al. (2011) found that year-to-year growth in Grebe numbers was positively related to brine shrimp density per Grebe from the preceding year at Great Salt Lake.
While dependence on and use of relatively few staging locations is a vulnerability, it also represents an important opportunity. Surveys conducted while Grebes are concentrated provide a population index that can be used to assess the species’ status and determine trends across years. Conservation and management professionals are capitalizing on this opportunity.
The Utah Division of Wildlife Resources conducts an annual survey at Great Salt Lake, and the Canadian Wildlife Service, the California Department of Fish and Game, and the Mono Lake Committee collaborate to survey Grebes at Mono Lake. For a time, Bureau of Land Management wildlife biologists surveyed Lake Abert – but now, East Cascades Audubon Society volunteers carry on surveys at the lake.
To assess the status of Eared Grebes, conservationists and wildlife managers can compare survey results to population objectives set by the Intermountain West Joint Venture’s Waterbird Conservation Plan. While surveys at Great Salt Lake and Lake Abert are expected to continue, organizers associated with Mono Lake are currently seeking funding to permit future surveys. Audubon is working with researchers to link these survey data across the Great Basin and to conduct bird trend analyses at priority saline lakes. Audubon’s efforts are driven by the recognition that the saline lakes operate as a network, not as individual lakes.
These monitoring efforts provide insight into how Grebe population numbers are changing, but resource managers need to understand what habitat conditions are driving these changes.
As mentioned previously, work at Great Salt Lake has linked Eared Grebe populations to brine shrimp densities. The brine shrimp harvest at Great Salt Lake is actively managed to sustain the brine shrimp fishery and to avoid negative impacts to birds, such as Grebes, dependent on brine shrimp as food. The conditions limiting Grebe populations likely vary from place-to-place, season-to-season, and year-to-year. Aside from food, other conditions potentially limiting Grebe populations include breeding habitat abundance, disease, and mass mortality events (such as bad weather) leading thousands of birds to crash land while migrating.
In short, successful Eared Grebe conservation and management depends on knowing which sites birds use and when, how their numbers change across sites and years, and which habitat factors are behind changing numbers. This approach applies not only to the fall staging season, but to other periods of the year as well.
At the Salton Sea in California, Eared Grebe numbers have shown a steep downturn during winter and spring in recent years. Historically, Eared Grebes were the most common waterbird present at the sea during winter and early spring, and large numbers passed through on their way to breeding grounds. The present decline is potentially linked to an increased salt concentration leading to disappearance of pile worms, an important food resource. Recent surveys suggest a return of a small percentage of birds, and they may be feeding on water boatmen, an aquatic insect. Critical questions remain unresolved including what sites might act as an alternative to the Salton Sea should poor conditions persist or worsen or how to manage conditions at the Sea to continue to attract some birds. Locations of alternative sites may emerge by applying techniques, such as automated telemetry networks, for tracking bird movements.
Eared Grebes are abundant as demonstrated by fall counts ranging from 2.6 to 5.6 million individuals from 2013 – 2017 at Great Salt Lake. However, this common species will not be kept common by accident.
Eared Grebes are vulnerable given their dependence on relatively few saline lakes that are threatened by water diversions, warming temperatures, and changing precipitation patterns. We need to remain vigilant by continuing to monitor at Great Salt Lake, Mono Lake, Lake Abert, and Salton Sea and by tracking birds to identify where birds might go instead of the Salton Sea. Through research, we need to understand better limiting habitat conditions and interactions of limiting conditions across sites, seasons, and years. This research should identify beneficial interventions, such as protecting and restoring flows to saline lakes. In combination, monitoring and research will allow us to understand where, when, and how to intervene so that this charismatic species remains a dominant part of the avian landscape.