Biodiversity Guide - The Intertwine

egional conservation strategybiodiversity guideChapter 5 Fish and Wildlife of the Regionally listed endangered species, is extirpated fromthe region (although the Oregon Zoo’s breedingprogram is augmenting the world’s small remainingcondor population). The yellow-billed cuckooalso is likely extirpated from the region; it and thestreaked horned lark are candidates for listing.Twenty-nine bird species found in the greaterPortland-Vancouver region are listed as eithersensitive or priority species of concern in Oregonor Washington; this includes four species listedas threatened or endangered in Oregon and/orWashington: the northern spotted owl (Oregon),American white pelican (Washington), sandhillcrane (Washington), and bald eagle (Oregon).The City of Portland has a more extensive list of58 special-status bird species that are supportedprimarily by riparian and riverine habitats,grassland, oak woodland or savanna, or matureconiferous forest.sity of Pacific Northwest forests require a detailedregional conservation effort aimed at reducing thepotentially deleterious effects of multiple land-usemanagement activities on ecosystem function andon important land bird breeding habitat.In the greater Portland-Vancouver regionthousands of publicly and privately owned acresare managed for timber harvest. These are verylarge forested areas with scattered clear-cutsand earlier successional shrub and forestlands.Forest age is a significant habitat limitation forbirds within the region because timber rotationon most commercial forests occurs about every40 years and the forests do not achieve matureor old-growth conditions. In addition, reforestingfor timber harvest tends toward Douglas firmonoculture without tree species diversity ormature, berry-producing shrubs in the understory.However, current practices typically resultin smaller clear-cuts than in the past, and timberharvesters have worked to reduce impacts onstreams, leave a few trees and snags, and generallycreate a more heterogeneous landscape in place.these species, so small patches of oak within theregion were considered inconsequential. However,recent research has begun to demonstrate thateven small patches of uncommon habitats may beimportant for regional conservation.A shift from open to more dense or closedcanopyoak habitat (because of fire suppression)has altered wildlife communities. For example,more open oak habitat such as savanna can supporthigher numbers of grass-nesting birds, aswell as species that use large, open-grown trees.Larger trees tend to have more nesting cavitiesand produce more lichens, which are a seasonallyimportant food resource for deer and elk, andacorns, which are important to many animals.The shift from savanna to woodland has also substantiallyreduced associated prairie habitat. Thedouble jeopardy of habitat loss and higher treedensity in remaining oak habitats has resultedin substantial declines of oak-associated wildlifespecies.Loss of Riparian HabitatsRiparian-associated birds, including birds thatuse small stream corridors, wetlands, floodplains,and bottomland hardwood forests, are decliningbecause of habitat loss and other factors. Nearlyall of the region’s wildlife uses water-relatedhabitats at some point in their lives. Only fivebird species—two of them non-native—are notassociated with any water-related habitat. Of the227 bird species known to occur annually in theManagement of Coniferous ForestsPortland-Vancouver region (see Appendix E), 92Coniferous forests in the Pacific Northwest supportsome of the highest densities of breedingof them (40 percent) rely on or are strongly associatedwith riparian areas and wetlands. Althoughland birds in North America, including manythe yellow-billed cuckoo has been consideredNeotropical migrants. A 2004 report by EnvironmentCanada 2 extirpated in the region, a single yellow-billedLoss and Degradation of Oak Habitatindicated that songbirds respond Among important avian habitats in the greatercuckoo was observed in 2009 in the Sandy Riverpositively not only to larger habitat patches, but to Portland-Vancouver region, aside from prairie,Delta. This sighting is a hopeful sign and a goodthe total amount of tree cover in a given region. oak habitats have shown the most significantreason to continue restoring contiguous bottomlandhardwood habitat. The yellow-billed cuckooIt is likely that part of this response is due to reduction in acreage and quality. Focal speciessuch as the white-breasted (slender-billed)increased connectivity in areas with more trees.does an excellent job controlling tent caterpillarA Seattle area study suggested 42 hectares (104 nuthatch and acorn woodpecker depend on thisinfestations and, unlike European cuckoos, doesacres) as a patch size at which most native forest habitat for the majority of their life cycle. Previouslyit was thought that only large, contiguousnot rely on other species to raise its young (i.e., itspecies were present (see also “Patch Size” inis not a nest parasite).Chapter 6). The unique habitats and avian diver-sections of oak habitat were enough to sustainRiparian forests are highly productive, providingleaves, dead wood, and abundant inverte-2 How Much Habitat Is Enough? A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas of Concern.96 97brates to the nearby ground and water. A healthyriparian forest has complex vegetation structurewith lots of native shrubs. Birds and other wildlifeuse these resources for food, cover, breeding,and—importantly—movement. The fairly linear,contiguous nature of streamside vegetation, coupledwith these resources and the availability ofwater, make riparian forests excellent movementcorridors for birds and other wildlife. In fact,riparian forests provide the majority of remainingconnectivity in urban and agricultural areas.Disruptions in these corridors come in the formof roads, bridges, and development and farmingpractices that fail to maintain sufficient riparianvegetation.Removal of Dead and Dying TreesApproximately 30 percent of bird species usestanding dead and dying trees (i.e., snags). Privateand some public landowners tend to remove deadand dying trees because of perceived hazards andaesthetics. Sometimes this is justified, but cuttingdown dead and dying trees also removes key elementsfrom ecosystems, thus diminishing theirfunctional value for birds and other wildlife.Nearly 100 wildlife species use snags in westernOregon and Washington forests, and morethan half of these species depend on cavitiescreated by birds. Primary cavity users are thosethat actually create cavities, such as woodpeckers.Secondary cavity users cannot create cavities;instead, they use cavities created naturally orby other species. For cavity-dependent species,absence of snags can be a primary limitingfactor, and long-term breeding bird survey datadocument declines in many cavity-dependentbirds. Local examples of cavity-dependent speciesinclude woodpeckers, western bluebirds,American kestrels, small owls, some bats, houseand Bewick’s wrens, nuthatches, chickadees andnorthern flying squirrel. Many other reptile,amphibian and small mammal species use cavitiesfor roosting and thermal protection. Hawks,eagles, and olive-sided flycatchers use snags forperches, and snags frequently serve as nestingsites for eagles and osprey.