Recovery Plan for the Northern Spotted Owl - DRAFT

BehaviorTehachapi Mountains of southern California. The northern and Mexicansubspecies were named by Merriam (1898) and Nelson (1903), respectively, onthe basis of plumage color and other morphological characters. Early naturalistsoften named subspecies on the basis of slight differences in plumage orsize variation. Thus, it was not surprising that Oberholser (1915) recommendedthat the California spotted owl and the northern spotted owl bemerged as one subspecies because of the large variation and overlap in plumagecharacters between the two subspecies. This recommendation apparentlywas not accepted by the American Ornithologists' Union (1957) Committee onNomenclature. More recently the American Ornithologists' Union Committeewas requested to reevaluate the subspecific status of the northern and Californiasubspecies. However, it declined to change the current designation becauseof a lack of adequate study of the subspecies characters (see discussionin Thomas et al. 1990:59). Nevertheless, the original boundaries delineatingthe subspecies' ranges were clearly arbitrary (Gould In Prep.).Barrowclough and Gutierrez (1990) attempted to elucidate the relationshipsamong the three subspecies using allozyme electrophoresis (a techniqueemployed to assess genetic variation). They compared patterns of proteinvariation at 19 presumptive loci among eight populations of the three subspecies.Surprisingly, they found no detectable variation among the Pacific Coastpopulations for any of the loci. One major allelic difference was found betweenthe coastal and Mexican subspecies. Thus, their results did not resolve thesubspecific relationships of cauina and occidentalis. However, lucida wasclearly a distinguishable taxon, and it probably has been separated from thecoastal forms for many hundreds of years (Barrowclough and Gutierrez1990:742).Low levels of genetic variation in wild populations are considered to be a threatto their evolutionary potential (Frankel and Soule 1981). This is because apopulation with low genetic variation would not have the variety of genes uponwhich natural selection could act to promote adaptation to changing environmentalconditions over evolutionary time. However, the lack of electrophoreticvariation in the coastal forms of spotted owl does not demonstrate unequivocallythat these subspecies are genetically depauperate. Barrowclough andGutierrez (1990) discuss possible alternative explanations for the lack ofelectrophoretic variation found in spotted owls.It is evident from the few studies conducted on the taxonomic and geneticrelationships of spotted owls that more needs to be learned to estimate bothcurrent levels of genetic variation in populations and hybridization with thebarred owl. A few California/Mexican hybrids are known from the wild (seeintra- and interspecific relationships). Hybridization is common among closelyrelated wild birds that are classified as separate species. The key issues to beresolved in evaluating hybridization as a threat to spotted owls is the extent ofhybridization (i.e., the levels of gene introgression), and the viability of hybrids.Barrowelough and Gutierrez (pers. comm.) currently are using advancedmolecular genetic techniques to help answer some of these questions.Adaptations of a Nocturnal Predator: Spotted owls are primarily a nocturnalpredator (Bent 1938). Like other nocturnal owls, spotted owls possessthree primary adaptations for night life: exceptional eyesight, exceptionalhearing, and modified feathers to facilitate silent flight (Payne 1971, Konishi1973, Clark et al. 1978, Martin 1986). Spotted owls are perch-and-pouncepredators (Forsman 1976). That is, owls select a perch and wait, trying tolocate potential prey either by sight or sound; once prey is detected, they try tocapture it with their talons. If prey is located in an inaccessible location or at14