Review of the Status of the Yellow-Billed Cuckoo in California: Sacramento Valley Populations

Abstract

Decline in populations of the western race of the Yellow-billed Cuckoo (Coccyzus ameri.. canus occidentalis) in California was noted by Grinnell and Miller in 1944, who stated: "because of removal widely of essential habitat conditions, this bird is now wanting in extensive areas where once found." The paucity of recent records (table 1) has led ornithologists to speculate that the Yellow-billed Cuckoo may presently be absent from much of its former range. Guy McCaskie (pers. comm.) suggests that the area above Laguna Dam on the Colorado River may be "the last stronghold for the Yellow-billed Cuckoo in California." The relative scarcity of reports in recent years may not reflect the Yellow-billed Cuckoo's status since this species arrives late in the spring (late May and June), nests in areas seldom visited by field ornithologists, and is furtive and thus easily overlooked. During July and August 1972, I located Yellow-billed Cuckoos at 15 localities along the Sacramento River in the Sacramento Valley , California (fig. 1). This paper presents data on the status and habitat of this population and reviews information concerning the past and present status and distribution of the Yellow-billed Cuckoo in the California region. METHODS A series of aerial photographs taken in March 1972 of the Sacramento River from the delta to Red Bluff (242 river miles) were used to locate riparian forest habitat. Census areas were selected to sample the range of available habitat. Areas were surveyed on foot for one or more mornings, using a tape recording of the kowlp call of the cuckoo. Habitat analysis was undertaken at 16 localities, 10 where cuckoos were found and 6 where a thorough investigation was made and no cuckoos were found (fig. 1). The following structural variables were considered (Emlen 1956; James and Shugart 1970): 1. Extent, length, and width of area 2. Per cent of (a) noncultivated, woody vegetation ; (b) open water (lakes, marshes, and sloughs exclusive of the main river channel); and (c) gravel banks, fields, and cleared areas 3. Spatial distribution of vegetation, considered in terms of the following four categories: E = even matrix (more or less randomly dispersed) I = uneven (variable coverage in indistinct clumps) C-in distinct clumps R = in distinct rows 4. Estimated height and per cent cover of canopy and understory 5. Estimated species composition of woody vegetation by per cent cover Spatial relationships of the five Yellow-billed Cuckoos observed on Todd Island, Tehama County, were mapped. The area occupied by each cuckoo was estimated and compared with observations from other localities. RESULTS Along the Sacramento River, 28 Yellow-billed Cuckoos were observed in 15 of the 30 areas where a thorough search was made. The cuckoos would respond typically to playback of taped calls by alighting near the observer in the crown of a willow (Salix) or cottonwood (Populus fremontii). There they would call at irregular and well-spaced intervals, spread their tails, and shuffle their wings, accentuating the white tail spots and the bright rufous patches on the primaries. I revisited four areas where cuckoos were found. Tape recordings were just as effective in eliciting a response as they had been on the earlier visits. Cuckoos were present only where the extent of riparian vegetation exceeds 300 m in length and 100 m in width. Cuckoos were not observed in the narrow (20-100 m wide) strip of apparently suitable habitat that borders the Sacramento River in many places (table 3; habitat analyses C, E, and F). Yellow-billed Cuckoos were observed only within 100 m of water. The species was most frequent in areas where extensive riparian vegetation is interspersed with lakes, sloughs, and/or marshy areas (table 2; habitat analyses 1, 2, 3, 5, 6, 8, and 10). Proximity of water to nesting site may reflect humid conditions in the cuckoo's population center in the eastern United States (Hamilton and Hamilton 1965). Cuckoos were usually found in willows and cottonwoods. These varied from stands 20-30 m high with a dense, woody, and herbaceous understory (table 2; habitat analyses 1, 2, 3, 6, 8, and 10) to low, shrubby, but dense stands of irregular distribution (table 2; habitat analyses 4, 5, and 7). On one occasion, a cuckoo was observed in an adjacent walnut [204] The Condor 76:204-209, 1974