90 



Birds — Our Lniiii^ Rc\onrci's 





<r;J.^ 



Fig. 2. Somhwestcrn vvilknv !!>- 

 catcher breeding tcmtciry in 

 tamarisk habitat along the 

 Colorado River in the Grand 

 Canyon. 



National Park, the USFWS, and the U.S. 

 Bureau of Reclamation have been regularly 

 monitoring the status of the southwestern wil- 

 low tlycateher in the Grand Canyon since 1982. 

 The National Biological Service's Colorado 

 Plateau Research Station at Northern Arizona 

 University has conducted this monitoring since 

 1992. The Grand Canyon is one of the few areas 

 with such a long record of willow flycatcher 

 population data; the only others are the Santa 

 Margarita and Kern rivers in southern 

 California. 



Methods 



Our monitoring program invohed intensive 

 surveys of about 450 km (280 mi) of the 

 Colorado River in Arizona between Glen 

 Canyon Dam (Lake Powell) and upper Lake 

 Mead. This portion of the river flows from ele- 

 vation 945 m (3,100 ft) at the dam to 365 m 

 ( 1.200 ft) at Lake Mead. We walked through or 

 tloated along all potential southwestern willow 

 flycatcher habitat patches along the river corri- 

 dor and looked and listened for willow tly- 



■V^- 



'"W-y. 



Fig. 3. Surveyor broadcasting 

 taped vocalizations and looking for 

 response from willow flycatchers. 





^^ 



catchers. Although willow flycatchers look very 

 similar to several other llycatchers, they can be 

 readily identified by their distinctive "tltz-bew" 

 song. To increase the chance of detecting resi- 

 dent llycatchers. we played a tape recording of 

 willow flycatcher songs and calls (Fig. 3) as we 

 moved through our survey areas. This technique 

 usually elicits a response from any resident 

 southwestern willow flycatchers that may be 

 present (Tibbitts et al. 1994). We conducted sur- 

 veys from May through July at about 160 habi- 

 tat patches each year (1992 and 1993). and 

 made repeated trips to each site (Sogge et al. 

 1993). 



Status and Trends 



Surveys conducted between 1982 and 1991 

 looked only at the upper 1 14 km (71 mi) of the 

 river and counted primarily singing males. 

 Within this same stretch, we detected only two 

 singing male willow flycatchers in 1992, and 

 three in 1993. These willow flycatchers were 

 found only in the dense riparian habitat domi- 

 nated by tamarisk, but including some willows 

 along the river corridor above 860 m (2,800 ft) 

 elevation. The breeding population of south- 

 western willow llycatchers in the Grand 

 Canyon was very low: we found only one nest 

 in 1992, and only three in 1993. Worse yet, each 

 of the three 1993 willow flycatcher nests was 

 brood-parasitized by brown-headed cowbirds 

 (Molothnis (Iter), and none produced young 

 willow flycatchers. With such a small breeding 

 population, and the potential for severe loss of 

 breeding effoil due to cowbirds. there is con- 

 cern over the continued survival of the species 

 within Grand Canyon. 



Based on comparison with past willow fly- 

 catcher surveys in the Grand Canyon (river mi 

 0-71: Brown' 1988, 1991), willow flycatchers 

 have declined since the mid-1980"s (Fig. 4). 

 Because we could conduct more surveys and 

 our methods were more likely to detect fly- 

 catchers than the pre- 1992 surveys (conducted 

 without using tape playback), the population 

 decline of the southwestern willow flycatcher in 

 Grand Canyon may be even more dramatic than 

 our data indicate. 



We did find willow flycatchers in areas of 

 the river corridor where surveys had not been 

 previously conducted: three in 1992 and five in 

 1993. Two other willow flycatchers were also 

 found during separate bird studies on the river 

 corridor. These birds were found in tamarisk 

 (above 530 m; 1,900 ft) or willow (below 530 

 m; 1,900 ft) habitats. None of these willow fly- 

 catchers established territories or bred, howev- 

 er, and most were probably migrants simply 

 passing through the area (Sogge et al. 1993). 



