SPRINt 1986 THESIS ABSTR^CT 47

THE PEREGRINEFALCON (Falco peregrinus) IN SOUTHERNBRAZIL; ASPECTS OF WINTER ECOLOGY IN AN URBAN ENVIRONMENT

The studywas undertaken in anurban environment of PortoAlegre, Brazil (30 02"S and 51 13"W), during2 austral summers(December 1978 to March 1979-January to March 1980). Sevenfalcons (4ctct; 3• •) were observed betweenDecember 1978 and March 1979. Five of the falconswere adults, 1 a juvenile and 1 of unknown age. The residentpair and 1 transient adult were phenotypically similar to the Attic Peregrine Falcon (Falcoperegrinus tundrius) in NorthAmerica. An adultpair of peregrineswere monitored for 540hours. Sequences of matingbehavior, such as aerial displaysand courtshipflights, were recorded during the study.The residentfemale showed strong territoriality towardsother females. The pair wasmost active during early morning and evening,and restedin mid-dayon shady ledges.Feeding activities increased from February to March,suggesting premigatory fattening. Foods of theresident femaleconsisted mainly of pigeons(91% of the preyremains), showing preference for fledglingstaken from nestson skyscraperledges. The residentmale fed mostlyon batsand passetines.Predation on batswas recorded mainly in Novemberand December. The residentfemale apparently took heavy prey (above 300 g) nearher pluckingledge and lightprey (below 100 g) when far away,implying an energy cost minimization in transportationduring the flight. The malewas more opportunistic in feedingbehavior than the female.-- Albuquerque,Jorge, LB. 1984.M.S. Thesis, Brigham Young University, Provo, Utah.

DISSERTATION ABSTRACTS

ELECTRORETINOGRAPHIC RESPONSES AND RETINAL ULTRASTRUCTURE OFTHE GREATHORNED OWL, Bubo virginianus'

Thisstudy was an investigationof the functionand ultrastructure of the retinaof the GreatHorned Owl (Bubovb•nianus). Gross physiologicalfunction of theretina was determined by electroretinography. Two procedures, dark-adaptation and flicker stimuli, were usedto determine the relative contributions of therod (scotopic)and cone (photopie) systems in theseretinae. A totalof 8 retinaefroth 4 GreatHorned Owls provided data for thisstudy. Owls were anesthetized and placed in a hand-builtoptical apparatus in whichlight of variouswavelengths and intensities could be delivered to the subject's eye. The dark-adaptation procedure revealed that the retina of this specieswas dominated by scotopic(rod-generated) components, asindicated by a slow,steady rise in/3-waves were also broad and roundedand had a fairlylong time course. This suggested that recovery of theretina following exposure to lightwas primarily due to an abundanceof rodsin theretina. Additionally, some cone activity was observed when high intensity single-flash stimuli were used. This wasindicated by prominenta-waves and/•-waves with steeper peaks and shorttime courses. Flicker ERGs revealed a scotopicfusion frequencyof approximately16 Hz. Photopiefusion frequencies were in therange of 35-45Hz whichwas quite lower than human and otherdiurnal primate retina. These data indicated that while cones were present in the GreatHorned Owl retinaand contributed to photopieresponses, the numberof coneswas low. Thisstudy was the first description of retinalultrastructure in theGreat Horned Owl. A totalof 10retinae from 5 GreatHorned Owls providedmaterial for electronmicroscopy. Subjects were euthanized and retinae were prepared according to standardprocedures. Ultrastructuralobservations of the retinaconfirmed previous observations by myself(Ault, Sd.,Raptor Research, 18(2):62-66, 1984) and others(Oehme, H., Der Zool.Jahrb. Abt. 2, 79:439-478,1961; Fire, K., VisionResearch, 13:219-230, 1973) that the retina of the Great HornedOwl possesses a high number of rods,but also contains some cones. Analysis of theultrastructure of theretina revealed typical neuro-anatomicalarrangements for a rod-dominatedvertebrate retina. However, several structures not previouslyreported for this specieswere also identified. These included: 1) thepresence of doublecones in thereceptor layer, 2) theapparent lack of electrical contactsbetween adjacent photoreceptors despite the presence of lateralfins on theinner segments, 3) themyelination of ganglioncell axonswithin the nerve fiber layer. Thisstudy concluded that the retina of theGreat Horned Owl is adapted to functionoptimally during the low illuminance levels at night.However, the presence of a functionalphotopie system and the ultrastructural arrangements of the retina may allow this owl to functionin thebrighter illuminances of theday. This owl is occasionally active during the day and its retina is apparently adapted for this possibilityand is not relegated to a strictnocturnal category. Such adaptation allows the Great Horned Owl to be an effective nocturnal predatorwhile at thesame time allowing it to expandits activity into the diurnal realin if needed. Ault, StevenJ. 1985. Ph.D. Dissertation.Idaho StateUniversity, Pocatello, Idaho. Presentaddress: Department of Anatomy, Universityof UtahSchool of Medicine,Salt Lake City, Utah 84132.Dissertation directed by Dr. EdwinW. House,Dept. of Biological Sciences,Idaho State University.