R. Roy Johnson

External threats: the dilemma of resource management on the Colorado River in Grand Canyon National park, USA

The United States Congress established Grand Canyon National Park in 1919 to preserve for posterity the outstanding natural attributes of the canyon cut by the Colorado River. In some cases National Park Service attempts to maintain Grand Canyons natural environment have been thwarted by activities outside the park. One of the most obvious external threats is Glen Canyon Dam, only 26 km upstream from the park boundary. Constructed in 1963, this gigantic dam has greatly altered the physicochemical and biological characteristics of 446 km of the Colorado River in Grand Canyon National Park. The rivers aquatic ecosystem has been greatly modified through the loss of indigenous species and the addition of numerous exotics. We consider this anexotic ecosystem. The riparian ecosystem has been less modified, with addition of a few exotics and no loss of natives—this we consider anaturalized ecosystem.The great dilemma now faced by park managers is that, after 20 years of managing resources along a river controlled by Glen Canyon Dam, the Bureau of Reclamation has proposed major changes in operational procedures for the dam. Scientists and managers from the National Park Service, Bureau of Reclamation, and cooperating federal and state resource management agencies are using a systems analysis approach to examine the impacts of various Colorado River flow regimes on aquatic, riparian, and recreational parameters in the park. This approach will help in the development of management alternatives designed to permit the most efficient use of that rivers natural resources without their destruction.

CACTUS FERRUGINOUS PYGMY-OWL IN ARIZONA, 1872–1971

Abstract The ferruginous pygmy-owl (Glaucidium brasilianum) has a wide geographic range centered on the Neotropics. At the northern edge of its distribution, 1 subspecies, the cactus ferruginous pygmy-owl (G. b. cactorum) reaches Texas and Arizona. However, in both states it has experienced important range and population declines. In Arizona in particular, the owl was originally described as common along several rivers and streams. There were many specimens collected and the subspecies was often mentioned in ornithological publications. Today, the cactus ferruginous pygmy-owl is found in low numbers in Arizona, and since 1997, it has been federally listed as endangered in that state. Determining when and why this owl began to decline sharply in numbers and range in Arizona has proven difficult. In retrospect, inadequate information apparently led to a lapse of several decades between the actual change in the population status and its recognition by ornithologists. Here we examine the most complete list of cactus ferruginous pygmy-owl records to date, including unpublished specimen collection records. Collectively, these records strongly suggest that a severe downward population trend began as early as the 1920s, not the 1950s, as is commonly reported in the literature. Using our revised time frame and the history of the cactus ferruginous pygmy-owl in Texas, we also examine possible reasons for the occurrence of the decline. The best information available might indicate a combination of biogeographic and human-related factors.

Identification of seismic crew noise in marine surveys by neural networks

With the increase in marine exploration in areas like the Gulf of Mexico and the North Sea, it is now quite common for multiple surveys to run concurrently and overlap one another. When more than one crew is actively shooting in the same area, there is a common type of interference that occurs due to the presence of more than one energy source. This interference—known as seismic crew noise—is recorded along with the desired true reflection energy.

Neural Network Approach to Seismic Crew Noise Identification In Marine Surveys

Marine surveys in many of today’s exploration hotspots encounter interference from other seismic crews shooting in close proximity. The crew noise interference appears as a pattern that can be readily identified by the human eye in seismic shot displays (Figure 1). To date, no efficient automated method has been established to remove these interference patterns prior to CMP stacking so that the data can be used for accurate amplitude versus offset (AVO) analysis. Neural networks have been used successfully in many geophysical applications due to their superior pattern recognition capabilities. The purpose of this study is to train a neural network to identify crew noise interference patterns for subsequent removal. The desired result is a clean pre-stack shot display that is ready for further processing.

BIOLOGY AND STATUS OF THE BLACK CATBIRD (MELANOPTILA GLABRIROSTRIS) IN BELIZE

Abstract We studied the poorly understood Black Catbird (Melanoptila glabrirostris), a near threatened mimid, at Lighthouse Reef in northeastern Belize. A resident of coastal lowlands and offshore islands, this endemic species of the Yucatan Peninsula has been reported as extirpated from several localities and has declined in numbers at other sites. We found it relatively common on the larger of two islands that comprise Northern Two Cayes from 18 to 25 June 2005. It had not been reported there since first discovered at Lighthouse Reef in 1862 and was considered extirpated until we rediscovered it. The Black Catbird at Northern Two Cayes displayed fierce intraspecific territoriality and both males and females defended against aggressors. However, it exhibited no interspecific territoriality toward its nearest avian associate, the Mangrove Warbler (Dendroica petechia bryanti). It used wing-flashing in territorial defense, mating rituals, and while foraging on the ground. We estimated ∼10 pairs of Black Catbirds in a 3-ha study area in the buttonwood-coconut (Conocarpus-Cocos) ecosystem but made no attempt to estimate the size of an apparently larger population in the more extensive area of coastal scrub on the remainder of the island. The defended territory of the pair studied most extensively was 100 × 25 m, centering on a buttonwood (Conocarpus erectus) grove and included numerous coconut (Cocos nucifera) trees.

Occasional Mimicry and Night-time Singing by the Western Curve-billed Thrasher (Toxostoma curvirostre palmeri)

Abstract The first instance of vocal mimicry is reported for the western subspecies of Curve-billed Thrasher (Toxostoma curvirostre palmeri). A Curve-billed Thrasher engaged in countersinging with a migrating Black-headed Grosbeak (Pheucticus melanocephalus) near Tucson, Arizona. Night-time singing by Curve-billed Thrasher is also documented for the first time. At least three responding Curve-billed Thrashers engaged in spontaneous song near Tucson, Arizona. Additional night-time singing was elicited by playback recordings

The Mississippi Kite in Arizona: A Second Record

ing the known breeding attempt. I have no records of the same nest being used in successive years, but in 1974 a pair of Merlins nested 1.8 km from an unsuccessful 1973 nest site. In 1972 I observed an adult male calling and circling at the same location where in 1973 the adult female was found dead by the nest. In eight breeding attempts (table 1), at least 20 young hatched and 15 fledged. Three nests failed altogether. These productivity figures are relatively low when compared with pre-pesticide estimates for Great Plains Merlins (Fox 1971) and recent data from Newfoundland (Temple 1972b), but they resemble recent data from the Canadian prairies (Fox 1971, pers. comm.). Three eggs that failed to hatch from a clutch which fledged one young were submitted to the Denver Wildlife Research Center for determination of organochlorine residues. The mean residue levels (wet weight basis) were DDE 9.40 ppm, dieldrin 0.80 ppm, and heptachlorepoxide 0.56 ppm. Polychlorinated biphenyls and toxaphene were not detected at a 0.05 ppm level of sensitivity. These residues represent moderate contamination and are sufficient to induce significant shell thinning and reduced hatching success (Fox pers. comm.). Fox (1971) and Temple (1972b) reported that Merlins currently lay thinner-shelled eggs, hatch fewer young, and produce fewer fledglings than in the pre-pesticide era. I offer sincere thanks to my friends and colleagues who volunteered data; to G. A. Fox, P. L. Wright, and C. M. White for editorial assistance; to E. Boeker and R. E. White of the Denver Wildlife Research Center for handling the pesticide analyses; and to the National Geographic Society, the Montana Cooperative Wildlife Research Unit, and the Montana Department of Fish and Game for funds. I owe special thanks to my wife Cathy and to my colleague Gus Wolfe for encouragement and field assistance.

The First Reported Hybridization of Abert's and Canyon Towhees (Pipilo spp.)

Abstract Two mixed pairs of towhees were found in irrigated desert yards near Tucson, Arizona. The first known towhee F1 hybrids, from a female Pipilo aberti (Aberts Towhee) and male P. fuscus (Canyon Towhee) were studied from winter of 1998–1999 through summer 2000. This mixed pair raised at least eight young in three broods during the two breeding seasons. Young were so similar to P. fuscus that, if seen outside this context, they would probably not be identified as hybrids. A second mixed pair, also near Tucson, suggests that hybridization between P. aberti and P. fuscus may be more common than originally thought. Lack of previously reported hybridization between P. aberti and P. fuscus may be either due to internal or external isolating mechanisms, limited survival and longevity, or human failure to recognize hybrids.