Patterns of Cavity-Entrance Orientation by Gilded Flickers (Colaptes chrysoides) in Cardón Cactus Author(s): Patrick W. Zwartjes and Shawn E. Nordell Source: The Auk, Vol. 115, No. 1 (Jan., 1998), pp. 119-126 Published by: American Ornithological Society Stable URL: https://www.jstor.org/stable/4089117 Accessed: 04-12-2018 00:34 UTC REFERENCES Linked references are available on JSTOR for this article: https://www.jstor.org/stable/4089117?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms American Ornithological Society is collaborating with JSTOR to digitize, preserve and extend access to The Auk This content downloaded from 130.166.29.140 on Tue, 04 Dec 2018 00:34:12 UTC All use subject to https://about.jstor.org/terms The Auk 115(1):119-126, 1998 PATTERNS OF CAVITY-ENTRANCE ORIENTATION BY GILDED FLICKERS (COLAPTES CHRYSOIDES) IN CARDON CACTUS PATRICK W ZWARTJES1 AND SHAWN E. NORDELL2 Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA ABSTRACT.-We studied patterns of cavity placement and orientation by the Gilded Flicker (Colaptes chrysoides) in the card6n cactus (Pachycereus pringlei) of Mexico, a columnar cactus characterized by a complex branching pattern. Overall, Gilded Flicker cavity entrances were oriented significantly toward the north-northwest, and they tended to face away from the rest of the cactus structure. There were more cavities proportional to the number of arms in the northwest quadrant, and these cavities had the strongest tendency to be oriented to the northwest and to face away from other arms. Cavities in the northeast quadrant were ori- ented slightly east of north, maintaining a strong pattern of orientation away from other cactus arms. Southwest quadrant cavity orientations were similar to those in the northwest quadrant but deviated from the trend of facing directly away from the bulk of the cactus structure. The fewest cavities proportional to number of arms were in the southeast quad- rant, and these showed no significant orientations, instead having the greatest variation in directional orientation as well as orientation with respect to other cactus arms. Received 24 March 1997, accepted 20 June 1997. THE EXCAVATIONS OF PRIMARY CAVITY-NEST- and Smith 1990). The saguaro is one of several ING BIRDS provide a record from which the eco- long-lived species of columnar cacti within the logical factors that influence cavity placement subfamily Cactoideae (Gibson and Nobel may be inferred. Several studies have used this 1986). It has a relatively simple morphological historical record to examine the patterns of cav- structure, remaining a single unbranched col- ity location and / or hole orientation in a variety umn until approximately 40 to 50 years of age, of bird species (e.g. Conner 1975, Conner and after which it may develop one to five lateral Adkisson 1977, Stauffer and Best 1982). Previ- branches that grow upward (Gibson and Nobel ous analyses have examined vertical distribu- 1986). Farther south in Baja California and So- tion, nest height (e.g. Nilsson 1984, Li and Mar- nora, Mexico, the cardon (Pachycereus pringlei) tin 1991, Albano 1992), and nest orientation for becomes the dominant columnar cactus (Wig- thermoregulation, either in terms of facing to- gins 1980). The structure of the cardon on the ward the sun in cold environments, or away eastern coast of the Gulf of California is more from the sun and/or toward prevailing winds complex than that of the saguaro. Cardons in hotter environments (Ricklefs and Hains- commonly have many branches that grow from worth 1969, Austin 1974, Inouye 1976, Inouye a central trunk at the base, often with no single et al. 1981, Finch 1983, Facemire et al. 1990, central stem, and they exhibit pronounced sec- Rendell and Robertson 1994). ondary branching on the longer primary Several studies have examined cavity dimen- branches (Borg 1956, Earle 1980, Wiggins 1980). sions, nest placement, and entrance orientation The region of the Sonoran Desert dominated by by Gilded Flickers (Colaptes chrysoides) and Gila the cardon also makes up a major portion of the Woodpeckers (Melanerpes uropygialis) in the sa- breeding range of both woodpecker species guaro cactus (Carnegiea gigantea) in southern that previously have been studied in saguaros Arizona (Inouye et al. 1981, Korol and Hutto in Arizona. 1984, McAuliffe and Hendricks 1988, Kerpez Studies of woodpecker nest-entrance holes in saguaro cacti have revealed that woodpeckers l Present address: Department of Biological Sci- tend to orient their cavities toward the north and ences, Humboldt State University, Arcata, California northwest (e.g. Inouye et al. 1981, Korol and 95521, USA. E-mail: [email protected] 2 Present address: Department of Biology, Califor- Hutto 1984; but see Kerpez and Smith 1990). In nia State University Northridge, Northridge, Califor- addition, Korol and Hutto (1984) reported that nia 91330, USA. cavity orientation was influenced in part by cac- 119 This content downloaded from 130.166.29.140 on Tue, 04 Dec 2018 00:34:12 UTC All use subject to https://about.jstor.org/terms 120 ZWARTJES AND NORDELL [Auk, Vol. 115 tus architecture. Specifically, when adjacent Mexico. We randomly selected 35 card6n cacti in se- branches were present on a saguaro stem, cavi- quence and recorded their morphological character- ties were oriented in the direction of least ob- istics. Linear measurements were made with a series struction. If a specific direction and avoidance of of interconnecting poles that were marked with red tape at 1.0-m intervals and white tape at 0.1-m in- obstructions are important factors influencing tervals. Height and length of each cactus arm (Fig. cavity placement and orientation, then the great- 1A) were determined by having one person hold the er architectural complexity of the cardon cactus pole vertically against the arm while a second person relative to the saguaro may force tradeoffs noted the measurements from a distance. The length among preferred orientation characteristics. The of an arm was determined to be the vertical distance various locations of the cardon arms, radially between the point where the arm originated from the distributed around a center point, will not be main trunk of the cactus (or a second arm) and the equally suitable for a woodpecker attempting to apex of the arm. A compass was used to determine achieve an optimal cavity orientation. For ex- the orientation of each arm (? 10) with respect to the ample, in the northwest region of a cardon cac- central axis (Fig. 1B). All angles were measured with respect to magnetic north and corrected to true north tus with respect to its center, orientation of the using a magnetic declination of 110 east (Defense cavity toward the northwest automatically plac- Mapping Agency 1991). The distance of each arm es the bulk of the cactus architecture opposite from the central axis was determined by measuring the entrance to the cavity. In parts of the card6n the horizontal distance from the midline of the trunk that do not correspond to a preferred compass to the farthest lateral extension of the arm (Fig. 1A). direction, woodpeckers must make tradeoffs be- Cavities constructed by Gilded Flickers can be dis- tween maintaining a preferred direction and tinguished from those made by other piciforms in orienting the cavity entrance to avoid obstruc- this region by their larger entrance dimensions (Gil- tion by the surrounding structure of the cactus man 1915, Harrison 1979, Korol and Hutto 1984, Mc- (sensu Korol and Hutto 1984). Auliffe and Hendricks 1988). Cavity size, shape, and depth were assessed from the ground with binocu- We quantified the architecture of cardon cac- lars. We recorded only those cavities that both in- ti in Sonora, Mexico, and examined the pattern vestigators agreed were fully excavated and could of distribution and orientation of nest cavities serve as functional cavities, based on apparent depth of Gilded Flickers within the structure of these and evenness in the circularity of the entrance hole. cacti. We tested the hypothesis that compass Each recorded cavity was designated "flicker" or orientation of cavity entrances and orientation "woodpecker" based on the size of the hole as with respect to cactus structure differ among judged by both investigators. Cavity placement and cavities located in the four quadrants defined orientation were recorded by measuring the height by north-south and east-west axes through the of each cavity entrance and the compass orientation center of the cactus. We predicted that these of each hole (Figs.1A, B). Each cactus arm and cavity was assigned to one of quadrants are apt to differ in ecological influ- four quadrants (i.e. NW, NE, SE, and SW) delineated ences because: (1) significant mean entrance by the north-south and east-west axes through the orientations to the northwest reported for cactus center. A cavity was placed in a specific quad- woodpecker cavities in saguaros suggest eco- rant by the orientation angle of the arm containing logical constraints on compass orientation; and the cavity (Fig. 1B); arms and cavities located in the (2) the location of the study site at 30?N latitude absolute center were not included in quadrant anal- precludes sunlight from shining directly on the yses. north side of the plant, thus creating a differ- Geometric equations incorporated as algorithms of ence in thermal conditions between northern a Fortran computer program were used to calculate quadrants and southern quadrants.