Barred Owls (Strix varia) historically inhabited the forests of eastern North America. During the last century, they expanded their range to include forests throughout the southern provinces of Canada, southeastern Alaska, British Columbia, Washington, Oregon, and northern California. To date, there has been no synthesis of the varied habitats or prey used by Barred Owls in their expanded range. Here I review and synthesize studies concerning habitat (N  =  114) and prey (N  =  43) of Barred Owls throughout North America north of Mexico. Barred Owls nested in wilderness areas and national parks as well as small suburban woodlots. They typically preferred old or mature, mixed deciduous/coniferous forests with fairly high canopy closure. Barred Owl nests in natural locations (N  =  341) were in cavities (74.8%), hawk nests (12.9%), tops of hollow trees (8.2%), squirrel nests (2.1%) and other locations (2.1%). Trees used by Barred Owls for nesting (N  =  169) included 22 genera, although one-fourth of all reported nest trees were Populus. Barred Owls used significantly more coniferous nest trees than deciduous nest trees in their expanded range vs. their historic range. They also nested in nest-boxes (N  =  103), in buildings (N  =  6), on nesting platforms (N  =  2), on the ground (N  =  2), in a creek bank (N  =  1), and under a bridge (N  =  1). Prey individuals (N  =  7077) obtained from pellets (N  =  5504) were mammals (74.7%), birds (8.3%), amphibians (6.4%), insects and spiders (5.6%), crayfish (3.0%), fish (1.5%), reptiles, snails and slugs, and earthworms (<1.0% each). The distribution of prey types documented by other means (e.g., observations, prey remains; N  =  1573) was significantly different, due especially to more earthworms in non-pellet samples: mammals (62.0%), birds (13.5%), insects and spiders (9.5%), amphibians (4.8%), earthworms (4.5%), fish (3.3%), reptiles (1.1%), snails, and crayfish (<1.0% each). The distributions of prey types in all samples that could be placed into winter or non-winter months (N  =  4631) differed seasonally, with more mammals in the winter diet (98.4%, vs. 58.9% in non-winter months) and more birds (11.9%), insects or spiders (11.4%), amphibians (10.7%), earthworms (2.3%), fish (2.0%), and crayfish (2.0%) in non-winter months.

We studied food habits, mechanisms of prey acquisition, and the effects of reservoir drawdown and fisheries management in a population of Bald Eagles (Haliaeetus leucocephalus) nesting on Shasta (Lake) Reservoir, a large impoundment in northern California used intensively for irrigation and recreation. Prey deliveries at seven nests were mostly bass (Micropterus sp., 55% of total prey biomass) and salmonids (14%), and all principal fish prey species were either introduced or regularly stocked. Carrion and moribund fish, mostly bass, accounted for >75% of successful foraging attempts. Fish mortality was related to spawning stress, disease, and catch-and-release angling; fish fatalities associated with bass fishing provided carrion throughout the breeding season. The proportions of fish species in the eagles' diet, as measured by prey deliveries to the nest, were positively correlated with those found in live-fish sampling and carrion surveys; all were predominantly bass. Benefits associated with seasonal and long-term reservoir drawdown included exposing spawning and foraging fish to eagle predation, and the likely release of nutrients and food for rapid fish growth upon re-inundation. Probable disadvantages of extended drawdown included loss of eagle foraging habitat and reductions in the standing crop of fish, likely resulting in competition among eagle pairs. Bald Eagle productivity was at or above average during the 2-yr study, a relatively wet period following a long drought and associated low pool levels, and we found a positive relationship between historic spring reservoir levels and Bald Eagle productivity from 1979–1999. Effects of fish introductions on trophic relationships and species composition warrant careful examination of eagle foraging requirements; however, past and present fisheries management appears to be currently benefiting the opportunistic eagles.

We analyzed Burrowing Owl (Athene cunicularia) reproductive performance (i.e., clutch size, brood size, and number of young fledged) in relation to nest and colony factors in Buffalo Gap National Grassland, South Dakota. We monitored 129 pairs of Burrowing Owls in 43 prairie dog (Cynomys ludovicianus) colonies in 1999 and 143 pairs in 45 colonies in 2000. Mean clutch size was 7.2 and ranged from 3–10 eggs. Pairs averaged 2.6 fledglings per nesting attempt and 76% of the nesting pairs were successful in fledging at least one young. Abandonment appeared to be the primary cause of nest failures. Variables measured at the colony level explained more (34–70%) of the variability in reproductive performance than did variables measured at the nest level (7–33%). In general, Burrowing Owls that arrived early, initiated clutches sooner, and either nested at greater distances from nearest neighbors or had fewer owl nests within 250 m of the nest burrow, had larger clutches, larger broods, and more fledglings. Seventy percent of prairie dog colonies were occupied by owls; most (85%) unoccupied colonies were <10 ha in size. Larger prairie dog colonies supported greater numbers of owl nests and consequently produced more total fledglings than did smaller colonies (P < 0.001).