Effects of Riparian and Wetland Restoration on an Avian Community in Southeast Arizona, USA

Abstract

We used a before-after-control-impact study across three years to assess the effects of active riparian restoration on bird densities and community composition. Birds density post-restoration on actively-restored plots averaged 25 birds ha-1 versus 15 birds ha-1 on controls. We conclude that active restoration should be pursued to benefit bird populations. Riparian and wetland habitats of the Western United States are exceptionally diverse because of their higher productivity and more complex vegetation relative to surrounding areas [1,2], but the destruction and modification of riparian and wetland habitats has resulted in population declines for numerous species [3]. The declining populations have triggered various reactions, including the expansion of legal protection, a focus on restoring degraded habitats, or creating new habitats where complete destruction has occurred. Although riparian avian species have been studied extensivelyespecially those species afforded legal protection, e.g., southwestern willow flycatcher, Empidonax trailli exemiuslittle published information exists as to the effects of active restoration on avian communities. Passive restoration efforts, such as the removal of livestock from riparian areas, have received greater attention than active restoration efforts [4]. A notable exception is the work of Rood et al. [5] along the Truckee River in Nevada, where active water management was used to restore a riparian forest. Active restoration of riparian habitats can include a variety of actions, including the installation of erosion control rock-and-wire gabions, mechanical manipulation of stream channel morphology, and pole planting of native riparian tree species, or, as Rood et al. [6] demonstrate, water regime management, among other techniques. Active wetland restoration can range from efforts to reestablish a native plant or animal community [7] to the wholesale creation of wetlands where they formerly existed [8]. All of these active restoration measures have the potential to affect numerous taxa, from the vegetative structure of the systems [9], to the invertebrate communities [10], to higher trophic groups such as birds. We studied avian community response to active riparian and wetland restoration efforts in the southeastern corner of Arizona using a Before-After-Control-Impact (BACI) study design [11]. The research addresses two questions: 1., How does active wetland and riparian restoration affect bird densi- ties relative to continuing passive restoration? 2., How does active wetland and riparian restoration affect bird community diversity relative to continuing passive restoration? We chose to monitor all bird species’ response to active restoration efforts for two reasons: first, birds are a trust group of the U.S. Fish and Wildlife Service, and second, they are highly visible species that may be used in ecosystem assessment [12,13]. We compare changes in bird density, avian species richness, and community composition across three years (one pre-restoration and two post-restoration).