OBSERVATIONS ON THE BREEDING ADAPTATIONS OF THE ROADRUNNER

ROBERT D. OHMART

Department of Zoology University of California Davis, California 95616

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 positive identification of two of the undyed partners. permanent resident in the arid and semiarid Three marked birds, along with mates of two, were regions of southwestern North America. Some collected and sexed to determine roles in feeding and features of its physiology are known (Calder 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 were recorded simultaneously. Ten young of known Calder 1968). However, the presence of age were preserved in alcohol to document various a salt-secreting nasal gland (Ohmart 1972) 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 inte- The Roadrunner has a bimodal nesting pat- grate physiological and ecological findings in tern in the Tucson area-mid-April to mid- an attempt to better understand the Road- June, and late July to mid-September. Ex- runners’ success in its hot, dry environment. treme heat and aridity in late June and early July, followed by rains in late July, separate MATERIALS AND METHODS 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 adults would have successfully reared clutches information on nest site and height (23 nests) was in both seasons, since spring nests were not recorded during the spring and summer of 1968, with allowed to reach termination. Eight pairs intensive field investigations from April through Sep- tember of 1969. A total of 269 hours of nest obser- which had nested in the spring were not fol- vations (using a 30~ spotting scope) were made on lowed again during the summer, either be- four nests (herein referred to as A, B, C, D) from cause members of the pair had been collected blinds situated 15-20 m away. Initially the birds or because of the time required to locate nests. seemed shy, but after 4-5 hr a pair appeared dis- The summer period involved three pairs, turbed only when the observer was outside the blind. 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 Cholla cactus (Opuntia spp.) is the most painted with black total solar absorption paint. A common nest site in the Tucson area. Of 23 thermometer inserted through a rubber stopper was nests observed (7 prior to 1969), 12 were in positioned so that the mercury-filled bulb was in the 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. (Celtis pallida), and 2 in palo Verde (Cerci- Core temperature readings of a nestling were ob- dium floridurn), Mean nest height for 16 tained with a telemetry unit produced by Sensory Sys- nests was 130 cm (range 40-245 cm). All 16 tems Laboratory of Tucson, Arizona. The unit was 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 bands of shade crossed the nest during the of the nestling. The sensor was implanted in the extreme heat of the day. right side of the peritoneal cavity and sutured in Clutch size, for seven nests where each egg place. Sensor placement was checked each afternoon was marked the morning it was laid, ranged when both parents were away from the nest. The 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 clutches of four eggs were completed on 16 dye on small areas of the brooding bird. At night a and 22 May. A clutch of two, completed on brooding parent could be approached and daubed 12 June, was the last active nest to be found before the onset of the July rains. Shortly 1 Present address: Department of Zoology, Arizona State University, Tempe, Arizona 85281. after the summer rains in July, the female [I401 The Condor 75:140-149, 1973 BREEDING ADAPTATIONS OF THE ROADRUNNER 141

TABLE 1. Instantaneous percentage growth rates (K) in nestling Roadrunners near Tucson, Arizona.

Age (days) C%/Kday,

o- 1 30.0 l- 2 26.6 2- 3 39.2 3- 4 30.1 4- 5 9.5 5- 6 14.5 6-7 14.2 7- 8 20.4 8- 9 22.6 9-10 15.1 10-11 12.1 11-12 11.3 12-13 -15.7 FIGURE 1. The relationship between body weight 13-14 - 8.9 and age in days in nestling Roadrunners. The letters 14-15 14.9 x and e denote body weights of two young in nest D 15-16 8.8 (fig. 3) in June (see text for full discussion). 16-17 11.3

that laid this clutch presumably constructed from nest D. Their weights at age 6 and 8 another nest 10 m away and laid a clutch of days agree closely with the general weight six. After the July rains, four complete curve, but body weights at 12.5 and 14.5 clutches contained four, six, six, and seven days show a decline from the expected. The eggs (Z = 5.7), respectively. younger was approximately 32% less, while Timing of egg deposition was determined the oldest deviated 12%. These two were directly in seven nests and indirectly by egg nestlings during June when a female, approxi- hatch sequence in four others. In seven of mately 1500 m to the northeast, laid a com- the nests, one egg was deposited each day, plete clutch of only two eggs. Both clutch and in three other nests, one egg was de- size and nestling weights were reduced as the posited every other day. The eggs of a two- hot, dry season approached. egg clutch were laid three days apart in mid- The weight values for Roadrunners in June. The incubation period for these clutches figure 1 were fitted to the appropriate weight was 17-18 days. increase equation discussed by Ricklefs ( 1967, 1968). The von Bertalanffy equation yielded NESTLING WEIGHT INCREASE AND the best fit. The asymptote was estimated at PLUMAGE DEVELOPMENT 300 g, K (weight increase) was determined The weight increase curve in figure 1 is based to be 0.0134, and t10-90 (time span in that on weights of 31 young of known age, a num- segment of the asymptote between lo-90%) ber of which were weighed two or more times. was 40.5 days. The mean weight at hatching was 14.2 g. By The naked nestling has been described as fledging time the mean weight had increased a “featherless, greasy, black” creature (Bent, approximately elevenfold; however, this was 1940). The only areas that are not black are only 50% of adult weight. The age at fledging the pink interramal region and the blue-gray was variable; two young fledged at 17 days, feet. six at 18, and two at I9 days. The hair-like white down is sparse and oc- Rates of weight increase for nestling Road- curs only in the pterylae. Between days I-2, runners were calculated from Brodys’ equa- the central rectrices and their upper coverts tion (1945:508) and are presented in table 1. are visible as developing pins. By days 2-3, Rapid weight increase occurred until day 4 early pins can be seen in the dorsopelvic and after which there was a general leveling off. femoral tracts, and the remiges and their After the first few days, weight increase upper greater coverts appear. At 34 days, ranged from lo-22% except between days 12- the central pair of rectrices are 6-7 mm; pairs 14 when the paucity of nestling weights 2-5 are progressively shorter with 5 about yielded values below the mean. 1 mm. Between days 5-6, the central rectrices Nestling weight and clutch size showed are 12-13 mm, and the tips of pairs 1 and 2 some seasonal changes. The two young desig- are beginning to rupture. Pin tips are visible nated x and e in figure 1 were nest mates from the lores posterior along the capital area krtling \gelda.) &5,5 lestling rgelda.)

2.11,10,9

h&7,6

i ic i c l ccci c ci ia*cI*c

(5,584

: 5,3,2 ?2 ci ie ccc i c i c.” l c l

4932.1

%2J.O

iic c i c 32AO 3,1,0.-l

Z,l,O;l 5 6 7 8 9 10 I, 12 13 14 15 15 17 I* 19 0 HOUR

0 FIGURE 3. Nest B showing similar correlations as figure 2.

ondary marginal coverts, dorsopelvic, and femoral regions give the nestling a sparse feather covering dorsally. Early brushes are beginning to show in the ventral cervical, FIGURE 2. Upper graph represents nest C and shows the correlation between age of youngest sternal, and abdominal regions. The pins of nestling and adult Roadrunners ’ freedom from nesting the interramal and submalar regions are just duties so that predator-prey activities can be synchro- rupturing, but pins of the malar, loral, ocular, nized. Food items fed to nestlings, black-bulb tem- and auricular regions are not yet ruptured. peratures, and parent activities at the nest are in- The alulars and coverts are showing as early cluded. Lower graph shows activity pattern of two species of Cnemidophorus lizards in southern Arizona brushes. By day 15, the central rectrices are ( Echtemacht 1967 ). about 77 mm and all pins have ruptured except those of the loral, ocular, and auricu- lar regions. At fledging (18 days), the pins to the posterior portion of the cervical region. of the above regions are just beginning to The pins of the dorsopelvic and femoral tract rupture, and the central rectrices are about are 2-3 mm long and the humeral and sternal 114 mm. regions are beginning to show pin tips. The secondary marginal and upper middle pri- CARE AND BODY TEMPERATURE mary coverts 6-10 also show as pin tips. Pins OF THE YOUNG of the abdominal region, under rectrix coverts, Throughout the daylight hours both parents and alula are about 0.5 mm. At 7-8 days, the tended the young (figs. 2, 3, 4). At dusk, all central pair of rectrices are 25 mm and all observations revealed the male going to sleep rectrices and their respective upper coverts on the nest, and frequent nightly checks veri- are ruptured, except for pair 5. The pins from fied that he remained on the nest. Each of the lores to the posterior cervical region range three brooding birds marked at night was a from 0.5-2.0 mm. Early brushes are scattered male. The female usually relieved the male through the dorsopelvic and femoral tracts. shortly after daybreak. As temperatures rose The longer proximal remiges and their coverts are beginning to rupture. Pin tips are begin- ning to show ventrally and anterioventrally TABLE 2. Tabulation of total number of feedings to the eye, in the auricular and malar regions. and lizards fed by each Roadrunner pair member for Pins are still present in the interramal, sub- three nests. malar, cervical, sternal, and abdominal re- Text Total items Lizards Hr nest gions, whereas the alula and under rectrix Nest figure a” 9 d 0 observed pins have ruptured. Between 9-10 days, the A 2 55 32 34 16 50.5 central rectrices are about 41 mm. The C 4 23 24 15 9 87.3 brushes of the capital, cervical, femoral, sec- D 3 27 44 10 17 100.0 BREEDING ADAPTATIONS OF THE ROADRUNNER 143

positioned with the tail into the breeze, thereby funneling air down and over the young. It could not be determined if the adult deliberately used its tail for shading. i IC‘ Z8. Generally, the tail was held horizontally or 25. 40 -4 o-

28 .A obliquely, but occasionally it was directed

ii ccc l c c l over the back, casting shade on the adults’ 21 body. A pattern of parental absence emerged as the youngest nestling reached 4-5 days of age (figs. 2, 3, 4). By this time, body size had tripled, yielding a more favorable surface- mass ratio for prevention of heat loss (table I), and the capabilities of heat dissipation were present (Lowe and Hinds 1969). By the time the still featherless nestling was 6 days old, the inattentive periods were extensive i l c ci c and corresponded with the activity period of the whiptailed lizards (Cnemidophorus spp.) (figs. 2 and 4)) the food item most frequently iici i* offered to nestling Roadrunners. Figure 3 shows some deviation from this pattern of

**i nest absence on 20 and 21 June, when, for unknown reasons, the female spent much time on the nest. Both adults provided food items for de- veloping nestlings, although the feeding effort 60. was quite variable between pair members 5a (table 2). Newly hatched young were typi- 12 I40. ___g,p;r(T_ cally fed insects (figs. 2, 3, 4), but whiptailed 2”:: d 5 6,: 7 6,,...... ,... 6 M II I2 13 14 15 16 17 I6 16 lizards comprised the greatest number of HOUR identified food items (113) fed to nestlings FIGURE 4. Nest D showing similar correlations as in 269 hr of nest observations (table 3). In figures 2 and 3. This nest contained the two nestlings conjunction with each food item offered, there designated by the letters x and e in figure 1. appeared to be a regurgitation of additional material from the parent to the nestling. This during mid- to late morning, the adults took possible regurgitation was observed in all turns shading the young, with wings slightly feeding until the time the nestlings were spread and drooped and the breast lowered to about 14 days old. Composition and quantity where it sometimes rested on the rim of the of the regurgitated material were not deter- nest. When shading, the adults were usually mined, but on two occasions the material was

TABLE 3. Food items consumed by nestling Roadrunners near Tucson, Arizona.

Vertebrate Material Arthropods

Nest Fig. A 2 50 (58)” 0 0 0 1 (1) 13 (15) 8 (9) 0 15 (17) 87 4 50.5 16 (35) 0 1 (2) 4 (9) 0 25 (54) 46 2 31.0 20 (43) 1 (2) !t (2) : (6) 2 (4) 15 (32) : (9) 1 (2) 0 47 3 87.3 D 4 27 (38) 0 0 0 3 (4) 1 (1) 16 (23) 13 (18) 11 (16) 71 2 100.0 Total 113 (46) 1 (0) 1 (0) 3 (1) 7 (3) 33 (13) 28 (11) 14 (6) 51 (20) 251 11 268.8 50% 30%

b Parenthetical values are percentages of total items fed at that particular nest except for those in the total line and these are percentages of the total. 144 ROBERT D. OHMART

60-

(b)

50.

-__ 20 ---______-_----~ (I,I,I,I,I,I~,~‘ ___--_ - ----3I~I~I!I~I!lil--

60. 8 12 16 l -• Nestling Core Temp. 0-O Black-bulb Temp. (a) N”\o-o o/O\o_o_o/O~O-O-O m Nest Unattended a Male On Nest a Female On Nest

FIGURE 5. a-d shows black-bulb temperatures, body temperatures of the youngest nestling, and nest inat- tendance periods by the adults. The nestling (from nest C, fig. 2) is 2 days old in a and 5 days old in d. Note in graph d the nest absence span of the adults and the ability of the 5-day-old nestling to limit its heat load. observed to be a clear, slightly viscous liquid. carried away from the nest on 11 June and The parent would present an insect or lizard presumably eaten. The final egg hatched on positioned anteriorly in the mandibles; the 16 June, and at 06:Ol on li’ June, I recorded young would grasp the food item and mandi- “Unmarked ( 0 ) bird came in and fed some- bles of the adult, first to consume any regur- thing small, regurgitating for 55 seconds, and gitated fluid and finally the food item. Dur- then consumed a fecal sac. It picked over the ing the transfer, the hyoid of the parent could young and the smallest nestling which was occasionally be seen moving, but for the most lethargic (he didnt’ beg when pecked) was part the flow appeared to be gravitational. thereupon eaten.” At 08:02 on 18 August, the The unions between the parents and young male from nest C consumed the youngest of when the presumed regurgitation was taking four nestlings. Whether the young had failed place ranged from 25-195 sec. After feeding, to beg is not known. or when a parent returned to the nest without The youngest of three nestlings in nest C food, the adult would consume small food had a telemetry unit implant to obtain body particles, ants, or fecal sacs in the nest. temperatures (Ti,). Its two siblings were 1 Frequently, an adult would prod and move and 3 days older. The Tb of the monitored the young about with its mandibles. Occa- nestling from age l-5 days ranged from 32- sionally, one of the adults would grasp a 42.3”C (fig. 5a-d). On the first 3 days (fig. nestling by the synsacral region and roughly 5a-c), the adults ’ initial morning departures move the squealing, struggling nestling. In and subsequent returns were similarly timed, two instances, the youngest nestling, which although the period of adult attendance at the was possibly lethargic, was picked up by the nest varied in length. On the fourth day (fig. head and consumed. In nest D, the first 5d), there was a broadening of the absence hatched young from a clutch of four eggs was span. The reduction in brooding and shading BREEDING ADAPTATIONS OF THE ROADRUNNER 145

601 jO\ONO\ 3 (d) / o/O- o-o-o\0 X0/O E ;‘ 50. ON” 0 ’ \ z O-0

3 0 ’ \ z 40. / ,.-.-*-.C*-*-.-.-*~.-. .._0 0-0 C /.\ 0‘ -O-/W* ?,Q .,/O \ 0 l \ lo O-0 a. */,-.-.‘ -o-o-o 2 30. I /O k! ?

z 60. 8 12 18 u) 0-0-o-o Q, (CI 0- -o-o,o_o~O\o6’ / b \ ,O ob, & 50. 0 No

2 6 OO’ \

2 i Q) 40 2 ,*-o-.-.,~_~_~~.-*-~-*-~ -.-.a 3 -*.o [&_....-‘ ’

0 0‘ 0‘

zc 30. /

time freed the adults to hunt lizards, where- DISCUSSION upon thermoregulation was left solely to the The Roadrunner is a relatively large (300 g), black, naked young. essentially flightless, diurnal carnivore endemic Gular flutter was observed in the tempera- to a region of very low primary productivity ture-monitored nestling at 16:30 on 17 August in North America. Other avian carnivores in (age 3 days). It may have begun earlier, but the desert are either smaller, nocturnal, or the young were aImost compIetely hidden by possess excellent powers of flight. Because the rim of the nest; notes on the young were of the unique niche occupied by the Road- obtained only when the nest was visited runner, it is not surprising that, during the briefly in the afternoons during the parents ’ evolution of the species, selection has resulted absence. in a number of highly specialized adaptations. The ability of the nestling to dissipate a Of the problems confronting the Roadrunner continuing heat load was observed on 19 in the unpredictable desert environment, that August at OS:40 (age 5 days). The nestlings’ which appears to be the most vital is pro- Th had been rising rapidly and, in the absence viding an adequate amount of food for its of the parents, it began dissipating heat and developing nestlings. maintaining a stable Tr,. At 09:17, the male Evolution of a bimodal nesting season di- visited the nest briefly and the nestlings’ Tr, rectly correlated with higher lizard and insect increased. The male left and the young again densities has resolved part of the problem. reduced its T,. In the Sonoran Desert this adaptation appears Temperature readings were taken every 2 to be common among avian species which hours throughout the night. Shortly after feed animal material to their young. It oc- dark, the nestlings’ T,, dropped to between curs in the Brown Towhee (Pipilo fuscus) 38.2 and 385°C and remained there until (Ohmart, pers. observ.), the Rufous-winged about 05:30. The brooding male and the two Sparrow ( Aimophila carpdis) (Ohmart 1969)) nonmonitored young were taken from the nest and the Curve-billed Thrasher ( Toxostoma at 03:OO on 20 August and cloaca1 TI;s were curvirostre) (E. L. Smith, pers. comm.). In found to be 38.5%. contrast, the totally granivorous Mourning 146 ROBERT D. OHMART

Dove (Zenaidura macroura) has a continuous sects to lizards than the other three broods breeding season from January-October, and studied, substantiate this. Insects were ade- some of the earlier hatched young may even quate to provide the energy required for breed later that same season (Irby and maintenance and growth until the young were Blankenship 1966). Lacks’ (1954, 1968) hy- 6 and 8 days old; but shortly after that, body pothesis that avian breeding seasons have weight did not increase normally, apparently evolved in direct relationship to the period because of the inability of the adults to meet when food is most abundant for the young the food demands of the young. The impor- has received support from a number of avian tance of selection of large food items for studies, and appears directly applicable to the feeding nestlings has been demonstrated in Roadrunner. Starlings (Sturnus vulgaris) (Kluijver 1933; Evidence in this study strongly suggests Dunnet 1955), the Great Tit (Parus major) that clutch size in the Roadrunner is regu- (Tinbergen 1949)) the Kingfisher ( Alcedo lated by food supply. The increase in mean atthis) (Swanberg 1952) and the Long- clutch size from the spring to the summer billed Marsh Wren (Telmatodytes palustris) breeding periods supports this assumption ( Verner 1965). The preponderance of lizards since the Sonoran Desert typically is much in the diet of the young Roadrunner has also more productive following the summer rains been referred to in other studies. Finley and than in the spring after a normal winter. Finley ( 1915:164) state, “Again came a liz- Under deteriorated habitat conditions (before ard-and again-and again-there was no use the onset of the summer rains), a complete counting. The larder was full of lizards and clutch of only two was laid, and two young nothing else.” Interestingly enough, the in- in a nearby nest were well below the normal tensive study of food habits by Bryant (1916) body weight. The female which had laid the in which stomach contents of 84 Roadrunners clutch of two presumably built another nest were examined, 16 during their breeding sea- predation pressure has allowed environments, that has a severe legacy for the evolution of asynchronous hatching, a desert inhabitation-a strikingly black skin at long nestling period, and a slow development hatching that is carried through the first criti- rate in the young. The weight increase fit to cal weeks of life of the juvenile that sits on the von Bertalanffy equation is significant in a relatively exposed platform nest.” that of the 105 species examined by Ricklefs Lack (1947) has suggested that asynchro- (1968) the growth of only 3 was best de- nous hatching might allow an immediate scribed by the von Bertalanffy equation. This method for adjusting food supply since the equation described rapid weight increase the younger siblings would be quickly removed first few days and then slowing of weight through starvation. However, in a few increase with the inflection point occurring clutches reported in the Roadrunner (Coues when approximately 30% of the asymptote 1903; Finley and Finley 1915; Sutton 1922) was attained. The three species best de- where there were large age differences be- scribed by the von Bertalanffy equation were tween siblings (about 18 days), the problem either sea birds or large terrestrial birds (34 of providing food for the young would be kg) which are relatively free from predation. aggravated by asynchronous hatching. While At the inflection point, the young Road- a narrow period of asynchrony would be runners are 9-10 days old, obtaining their advantageous, an extended age difference first feather covering and probably beginning among nestlings would aggravate the problem to maintain a stable body temperature. At of providing food for the young. Food de- 7 days, the naked young require little diurnal mands would be set by the older nestlings, protection, but are still brooded at night. whereas adult attention to the nest would be Asynchronous hatching is diametrically op- controlled by the youngest nestlings. Unfor- posed to a short nestling period and could tunately, we have no knowledge of the fate only have evolved if predation pressures were of these seemingly unusual nests. In all the low. Asynchronous hatching allows a broader nests that I have observed, 7 days was the distribution of nestling food demands, and greatest disparity between the first and last this apparently has been important in the egg; Bendire (1878) examined 20 nests and evolution of the reproductive scheme in Road- his data are essentially in agreement with my runners. The paucity of diurnal prey species findings. has forced the Roadrunner to specialize in Asynchronous hatching not only distributes single, large food items (lizards) which are the food demands of the young over a broad carried one at a time to the nest. The ne- period; it also provides a mechanism, which cessity of both pair members being free to in the event of a diminishing food supply, hunt whiptailed lizards during the single ac- brings about removal of the youngest sibling tivity period of the lizards is obvious. When competitors. In the desert, the food supply is possible, a long nestling period appears to be frequently erratic and productivity can be re- more advantageous in birds; Lack (1948, duced rapidly and drastically by hot, dry 1954) and Nice (1957) have presented evi- winds. Should the food supply wane during dence which indicates that the length of the the incubation period, the brood size of Road- nestling period is positively correlated with runners can be regulated by the adults ’ eat- nestling success. ing the young. Interestingly enough, brood While this paper deals with the evolution reduction has been reported for another of breeding adaptations in Roadrunners, it Sonoran Desert species, the Curve-billed should also be pointed out that specialized Thrasher ( Toxostoma curvirostre) (Ricklefs adaptations have evolved for existence during 1965). However, the thrashers take a less the lean winter months when other large avian active role than Roadrunners; reduction of carnivores, hawks and owls, have migrated their broods occurs by the starvation of nest- to more productive regions. Physiological in- lings. The Lesser Roadrunner (Geococcyx formation on the capability of the Road- v&ox), a more tropical species, apparently runner to enter hypothermy spontaneously does not lay clutches of such variable size and then to use low intensity solar energy, and appears not to have evolved asynchronous instead of biochemical stores, to increase and hatching ( Miller 1932). maintain its T,,, suggests strong selective 148 ROBERT D. OHMART forces operating for energy conservation nestlings in a clutch begin to reach their maxi- (Ohmart and Lasiewski 1971). The reduc- mum as the youngest nestling is about 7-8 tion in arthropod and lizard densities and the days old. At age 4-S days, the black-skinned increase in the diet of vegetable material young has grown large enough so that the (Bryant 1916) would make energy conserva- parents can leave it unattended in the early tion necessary during the cold season (Sutton morning hours ( 06:30-08:OO) without it un- 1967; Geluso 1970). Roadrunners, in an ap- dergoing a severe body temperature drop. parently permanent pair bond, live on their The black young then begins to absorb solar territory year around and may defend it radiation and increases its body temperature during the winter months to insure an ade- ( 08 :O&O9 :30). Gular flutter and alignment quate food supply for the adults themselves. in the bands of shade are used to limit the The Lesser Roadrunner does not possess heat load. The water lost in gular fluttering dorsal cutaneous melanization (Udvardy, pers. and cutaneous evaporation is then counter- comm. ) ; this trait would be necessary for it balanced by the excretion of salts by the salt- to achieve the degree of solar absorption ob- secreting nasal gland and by the adults ’ possi- served in the Roadrunner (Ohmart and ble regurgitation of a clear liquid to the nest- Lasiewski 1971). ling at each feeding. These physiological and The Roadrunner possesses a number of behavioral interrelationships allow complete adaptations which are unique to the genus. synchrony of predator-prey activities. The It differs from the congeneric Lesser Road- young are shaded by the adults in the early runner in possessing dorsal cutaneous melani- afternoon hours. Should the food supply zation in the adult, asynchronous hatching, diminish during the nestling period, the youn- a highly variable clutch size, and a greater gest nestlings are consumed by the adults. body weight. Possession of a salt-secreting nasal gland and the ability to go into hy- ACKNOWLEDGMENTS pothermia may also be unique to this species. Asynchronous hatching appears to be I thank W. J. Hamilton III, 0. W. Johnson, J. B. present only in the north temperate members Leigh, R. J. Raitt, Jr., G. M. Sutton, D. W. Tinkle, and S. M. Woodward for their comments and help of the family, and may have evolved in re- during the preparation of the manuscript. I am par- sponse to lower food availability and/or an ticularlv indebted to Susan M. Woodward for her erratic food supply. Cutaneous melanization invaluable help and patience in collecting nest obser- in nestlings appears to be common to all spe- vation data. Her comments and criticism during the study were most helpful. The help and cooperation cies in the family. of Mr. and Mrs. S. W. (Buck and Sally) Fletcher is deeply appreciated. The work was conducted while SUMMARY I was sunnorted bv PHS training grant ES 00101-03. This paper is dedicated to the-memory of Padre General observations of 23 Roadrunner nests (Loye H. ) Miller in gratitude for his encouragement and 269 hr of observations of 4 specific nests during the study, and for his friendship. reveal that both the young and adults possess many specialized adaptations for breeding in LITERATURE CITED the southern Arizona desert. Placement of the BENDIRE, C. 1878. Breeding habits of Geococcyx platform nests is primarily in round-stemmed californianus. Bull. Natl. Ornithol. Club 3:39.’ cholla cactus, allowing direct sunlight while BENT, A. C. 1940. Life histories of North American simultaneously providing scattered bands of cuckoos, goat suckers, hummingbirds, and their shade. Nesting periods coincide with greatest allies. U.S. Natl. Mus. Bull. 176:36-51. food abundance and clutch size appears to be BRODY, S. 1945. Bioenergetics and growth. Re- related to food supply during the egg-laying printed 1964. Hafner, New York. BRYANT, H. C. 1916. Habits and food of the Road- period. Incubation begins with the laying of runner in California. Univ. Calif. Publ. Zool. the first egg, yielding young of different ages 17:21-50. in the nest. Whiptailed lizards are the pri- CALDER, W. A. 1968. The diurnal activity of the mary food items offered to the nestlings and Roadrunner, Geococcyx californianus. Condor these lizards have a single activity pattern 70:84-85. which begins about 07:OO and terminates CALDER, W. A., AND P. J. BENTLEY. 1967. Urine concentrations of two carnivorous birds, the about 13:O0. It is of utmost importance that White Pelican and Roadrunner. Comp Biochem. both adult Roadrunners be free from brooding Physiol. 22: 607-609. or shading the young to hunt lizards during CALDER, W. A., AND K. SCHMIDT-NIELSEN. 1967. the lizards ’ short period of activity as the Telnperature regulation and evaporation in the Pigeon and the Roadrunner. Amer. J. Physiol. growing nestlings require increasingly larger 213:883-889. quantities of food. The food demands of CALDER, W. A., AND K. SCHMIDT-NIELSEN. 1968. BREEDING ADAPTATIONS OF THE ROADRUNNER 149

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