Populations of avian transients were studied at a stopover area in southern Texas during four consecutive migration seasons, fall, 1973-spring, 1975. We captured individuals by mist net for banding and fat level determination. Concurrently we made observations on behavior of free-flying birds.We worked intensively with a single species, the Northern Waterthrush (Seiurus noveboracensis) while gathering weight fat and behavioral data on other species as well. Many of the patterns of weight change and behavior seen in the Northern Waterthrush were observed in other common passerines which occurred as transients on our study site.Results showed that birds in Zugstimmung and Zugdisposition differ, not only physiologically but behaviorally as well. Individuals of normally non-gregarious species that are in Zugstimmung are gregarious and stay in an area for only a short period. Their habitat needs are broad since these birds are not dependent on the food resources of the area in which they stop while in this physiological state. In contrast, normally non-gregarious migrants in Zugdisposition are hyperphagic and aggressively territorial in defense of resources and may stay at the same site for several days. Their habitat needs are quite specific since they must increase food intake by as much as 40% to build up fat reserves. Not all individuals in Zugdisposition are able to find territories at the same time. Those birds unable to claim territories either continue to migrate or stay in an area as floaters, continually attempting to obtain territories. Weather conditions probably act as a third variable that must be balanced by the individual in a complex optimization strategy with physiological state and success in competition.

We investigated fat deposition in transient, nocturnal, long-distance migrants at a wooded stopover site that is not near an ecological barrier (e.g. desert, large water body). The changes in body mass of recaptured birds have traditionally been used as a measure of mass gains at stopover sites. This technique ignores the majority of transients, however, possibly hindering the ability to answer species-level questions regarding stopover mass gain. We compare an analysis of recaptures with a technique that considers all captures and their condition by time of day. Eleven woodland-associated migrant species were analyzed, as well as a resident species (Black-capped Chickadee, Parus atricapillus) for comparison. Based on recapture data alone, our study site appears to be primarily a location of mass loss, rather than one of fat deposition. Conversely, the examination of condition by time of day suggests that individuals of several species have net daily gains greatly exceeding those of recaptured individuals. During autumn, however, several species exhibited net daily losses. Although some of these losses may be related to molt, it seems unlikely that molt is the only contributing factor. Differences among species in mass gains at our site suggest that various fat-deposition patterns (and, thus, migration strategies) may occur among migrants that are not approaching ecological barriers.

No abstract

THE Sierra Madre or Bailey's Sparrow, Xenospiza baileyi, was described as a new genus and species from the high mountains of Durango and Jalisco less than 35 years ago (O. Bangs, Proc. •Vew England Zool. Cl., 12: 85-88, 1931). It has since been considered rare, and even 19 years ago, when F. A. Pitelka (Condor, 49: 199-203, 1947) described a new subspecies, only 11 specimens were known, of which he had at hand only 1 from La Cima, Distrito Federal, and 3 from western Mexico. Today the population from the sacaton bunch grass areas of La Cima, in the pass between the Valley of Mexico and Cuernavaca, is well represented by series in the collections of Phillips and the University of Minnesota Museum of Natural History. These series include specimens in all the plumage stages from stubby-tailed juveniles to worn adults and those having recently completed the prebasic molt. Other specimens are scattered through several museums in the United States. The population of Durango is now represented by additional specimens in the collection of the Robert T. Moore Laboratory of Zoology, Occidental College. With the accumulation of this material, and notes from several seasons' field work by the authors, it is a propitious time to gather together the information on this restricted endemic Mexican sparrow.

Radio transmitt ers were successfu lly placed on 10 barred owls (Strix varia) during 59.65-66 and the movemen ts of the owls were followed with an automatic radio-tra cking system for a total of 1,182 days. More than 28,000 owl locations were sampled from some two million locations recorded. These locations , along with habitat availabil ity informati on, were programme d for computer analysis to determine intensity of habitat use. Barred owls showed consisten t and highly significa nt preferenc e or avoidance for different habitats despite changing seasons, phenology , weather condition s, and years.The order of habitat preferenc e in decreasin g intensity of use was oak (Quercus spp.) woods, mixed hardwoods and conifers, white-ced ar .' (Thula occidenta lis) swamps, oak-savan nas, alder (Alnus spp.) ..amps , 4marshes, and open fields.