Observations on the Breeding Adaptations of the Roadrunner

The Roadrunner (Geococcyx californianus) is with a dye-saturated cotton ball affixed to the end a diurnal ground-dwelling cuckoo, which is a of a stick.Scratch marks on the mandibles allowed permanent resident in the arid and semiarid positive identification of two of the undyed partners.regions of southwestern North America.Some Three marked birds, along with mates of two, were features of its physiology are known (Calder collected and sexed to determine roles in feeding and brooding.and Bentley 1967; Calder and Schmidt-Nielsen Weights of nestlings were obtained in the field on 1967; Calder and Schmidt-Nielsen 1968; a triple beam balance; notes on plumage development Calder 1968).However, the presence of were recorded simultaneously.Ten young of known a salt-secreting nasal gland (Ohmart 1972) age were preserved in alcohol to document various stages of development.and studies on the efficiency in body water turnover in birds under simulated desert con-RESULTS ditions (Ohmart et al. 1970) indicated that BREEDING SEASON AND NESTING detailed field information was needed to integrate physiological and ecological findings in The Roadrunner has a bimodal nesting patan attempt to better understand the Road-tern in the Tucson area-mid-April to midrunner' s success in its hot, dry environment.June, and late July to mid-September.Extreme heat and aridity in late June and early MATERIALS AND METHODS July, followed by rains in late July, separate the breeding periods.All field observations were conducted in an area 7 I could not determine whether individual miles S and 7 miles E of Tucson, Arizona.General information on nest site and height (23 nests) was adults would have successfully reared clutches recorded during the spring and summer of 1968, with in both seasons, since spring nests were not intensive field investigations from April through Sep-allowed to reach termination.Eight pairs tember of 1969.A total of 269 hours of nest obser-which had nested in the spring were not folvations (using a 30~ spotting scope) were made on lowed again during the summer, either befour nests (herein referred to as A, B, C, D) from blinds situated 15-20 m away.Initially the birds cause members of the pair had been collected seemed shy, but after 4-5 hr a pair appeared dis-or because of the time required to locate nests.turbed only when the observer was outside the blind.The summer period involved three pairs, Black-bulb readings were noted hourly, or when-which renested after the spring season, and ever one of the parents came into or left the nest.two pairs of unknown spring status.The black-bulb consisted of a metal commode float painted with black total solar absorption paint.A Cholla cactus (Opuntia spp.) is the most thermometer inserted through a rubber stopper was common nest site in the Tucson area.Of 23 positioned so that the mercury-filled bulb was in the nests observed (7 prior to 1969), 12 were in center of the float.The system was suspended nest staghorn cholla (0. wer.sicoZor), 6 in jumping high beside the blind and fully exposed to solar cholla (0. fulgida), 3 in desert hackberry radiation.Core temperature readings of a nestling were ob-(Celtis pallida), and 2 in palo Verde (Cercitained with a telemetry unit produced by Sensory Sys-dium floridurn), Mean nest height for 16 tems Laboratory of Tucson, Arizona.The unit was nests was 130 cm (range 40-245 cm).All 16 positioned below the nest, with the recording lead nests were constructed in such a way that passing through the center of the nest to the dorsum of the nestling.The sensor was implanted in the bands of shade crossed the nest during the right side of the peritoneal cavity and sutured in extreme heat of the day.place.Sensor placement was checked each afternoon Clutch size, for seven nests where each egg when both parents were away from the nest.The was marked the morning it was laid, ranged unit was calibrated to the nearest O.l"C.from two to seven with a mean of 4.6.Two A member of each pair was marked with orange dye on small areas of the brooding bird.At night a clutches of four eggs were completed on 16 brooding parent could be approached and daubed and 22 May.A clutch of two, completed on 12 June, was the last active nest to be found