The Cactus Wrens on the Santa Rita experimental range, Arizona

Anderson, Anders; Anderson, Anne

From the beginning of 1953 to the middle of 1956 we studied a population of Cactus Wren (_Campylorhynchus brunneicapillus_) on the Santa Rita Experimental Range, 35 miles south of Tucson, AZ. The vegetation of the 60-acre plot was a cholla assoc. broken by washes bordered chiefly with mesquite and palo verde trees. We found 16 first brood nests in 1953, five in 1954, five in 1955, and eight in 1956. The Curve-billed Thrasher population did not fluctuate to a similar extent. Predators were not common. Thrashers destroyed many of the roosting nests of the Cactus Wren, but this probably had little effect on the total population. The carrying capacity of the area may have been exceeded in 1953; the following years, perhaps, should be considered normal. It is suggested that disease may have caused the reduction in population. Egg laying occurred a month later than at Tucson. The range area was 900 ft. higher in elev. than the Tucson locality. Its max. temps were 3 degrees F. lower in the daytime; and because of inversion, the night temps were 3 degrees F. higher. With average temperatures identical in the two places, we assume that egg laying was delayed at the range possibly because of the slower onset of warm spring temperatures there.

The Cactus Wrens on the Santa Rita experimental range, Arizona

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