Riparian restoration in the southwestern United States frequently involves planting cottonwood (Populus spp.) and willow (Salix spp.). In the absence of flooding and gap-forming disturbance, planted forests often senesce without further young tree recruitment. This has largely been the case in California riparian systems that historically supported state-endangered western Yellow-billed Cuckoo (Coccyzus americanus; Cuckoo). A decline in Cuckoo population numbers in the past 30 years has been associated with forest maturation. Other riparian species of concern show a concomitant decline, indicating the problem is not specific to Cuckoos. Although varying hypotheses exist for recent decline, alternative management practices have not been sufficiently explored to rule out breeding ground habitat quality as a major contributing factor. Few intensive Cuckoo datasets exist to test hypotheses about breeding habitat quality due to extremely low populations in the remaining occupied sites. We used a historical (1986-1996) spot mapping dataset from the South Fork Kern River Valley, CA to identify vegetation characteristics related to Cuckoo and five other sensitive riparian bird territory densities. We found Cuckoo densities were positively associated with increased vertical vegetative structure 1-5 m above ground with a threshold for mean tree height. Sensitive species densities were also related to vertical structure and started to decline with stand height greater than 6-8 m. Naturally regenerated sites had higher densities of most sensitive bird species than planted sites. We provide ideas for restoring mature forest with little vertical structure.

The rusty blackbird (Euphagus carolinus) is a species of conservation concern throughout its range and the cause of the species' population decline is unknown. We studied diet composition of rusty blackbirds with stable isotope mixing models in suburban landscapes in the southeastern United States. We captured blackbirds in Georgia and South Carolina from 2009 to 2012, and estimated proportions of earthworm, other animals, pecan, and acorn incorporated into individual diets. On the Piedmont Plateau, terrestrial and aquatic earthworms constituted the largest proportion incorporated into the diet (39% AE 2.9; mean AE SD by site and year) and animals other than earthworms (mostly larval invertebrates Odonata and Diptera) constituted 27% AE 12.9. In contrast, on the Coastal Plain, which featured milder winters than the Piedmont, earthworms constituted a lower proportion (19% AE 1.2) of incorporated food items and animals other than earthworms comprised 62% AE 3.3% of the diet. Increased incorporation of earthworms in the diet was related to increased upcoming precipitation and daily maximum temperature. Rusty blackbirds incorporated more tree mast into their diet on the Piedmont Plateau than the Coastal Plain. Increased incorporation of tree mast was related to advancing cold temperature. Mast, including crushed pecans (Carya illinoenensis) and pre-opened small-seeded red oak (Quercus spp.) acorns, is a high-lipid dietary component of blackbirds wintering in colder climates, and is incorporated prior to extreme cold weather. Therefore, planting mast trees, especially lipid-rich pecan, could be used to augment resources in known rusty blackbird wintering hotspots. Maintaining shallowly flooded wetlands with a fluctuating water regime and residential lawns with abundant red oak (Quercus spp.) leaf litter would promote acorn and invertebrate resources including earthworms. Ó 2015 The Wildlife Society.

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Western Yellow-billed Cuckoo (Cuckoo; Coccyzus americanus) populations continue to decline in the western United States despite efforts to increase availability of riparian forest. Cuckoos have unique breeding habitat requirements such as large contiguous tracts of riparian forest (>80 ha), large estimated home ranges (20-90 ha), and dense vertical structure around the nest. However, local habitat-scale features may be missing in landscapes of predominantly mature riparian forest that may need to be specifically managed for nesting. We used historical nest data (n = 95) from the South Fork Kern River Valley, California, from 1985 to 1996 to identify important nest site features that may be missing in current riparian forests. We found that increased canopy cover and vertical structure at all levels in the canopy greatly increased the probability of Cuckoo nesting. With smaller estimated effect sizes, the probability of Cuckoo nesting increased with increasing willows and forbs and smaller mean tree dbh. Cuckoos selected plots with disproportionately high percent willow cover relative to availability plots regardless of whether sites had low or high percent willow available. Counts of fledged young were positively related to willow percentage. No vegetation variable influenced daily survival rate which was 0.991 (LCI = 0.980, UCI = 0.996). Overall 17-day nest success was likely high (0.86, LCI = 0.71, UCI = 0.93). In the absence of natural processes that create early successional stage forest, specific management for early successional stage forest is needed to increase the probability of Cuckoo nesting and nest productivity.