Diving Differences between Western and Clark's Grebes

In the sixth edition of the A.O.U. check-list (1985), Clark's Grebe (Aechmophorus clarkii ) was designated a separate species from the Western Grebe (A. occidentalis ). There is considerable local variation in the relative abundance of the two species, and they are sympatric throughout much of their range. In areas where both are common, they frequently form mixed feeding flocks, but their Advertising vocalizations are distinct, and interbreeding is rare. Nuechterlein (1981) found that Clark's Grebes were more likely than Western Grebes to engage in "springing dives", in which the diving bird initially pulls its head back, then springs upward with the legs and leaps out of the water before submerging. Nuechterlein (1981) speculated that birds engaging in springing dives may attempt to dive more vertically and this form of dive was related to the depth an individual bird reached. This would result in ecological segregation between the two species. The major purpose of this study was to document a possible relationship between the level and springing dives and the depth of water at which they occur in these two grebe species.