OOS 44-4
Riparian habitat dynamics of the western yellow-billed cuckoo and prospects for habitat expansion on the Sacramento River in California
The western yellow-billed cuckoo (Coccyzus americanus) is a Neotropical migrant bird that is listed as an endangered species in California and is currently under review for listing as a threatened DPS under the federal Endangered Species Act. The population on the Middle Sacramento River was once the largest remaining population of cuckoos in the state but recently declined.
Research questions: (1) How much riparian vegetation and cuckoo habitat was lost between 1952 and 1987? (2) How does cuckoo sub-patch habitat structure (i.e. area and width) change over time? (3) How does the habitat sub-patch mosaic shift in space with respect to time? (4) How accurate is the sub-patch habitat model (using patch size, width, and land age as a surrogate variable for cottonwood) at predicting presence or absence of cuckoos? (5) Where can cuckoo habitat be expanded on the Sacramento River?
A geospatial analysis of two time periods (1952 and 1987) of a 127-km study reach of the river (river miles [RM] 155-234) documented creation, spatial shifts, and loss of cuckoo habitat patches due to fluvial geomorphic processes, vegetation recruitment, and succession. The spatial co-occurrence of riparian vegetation on floodplains <65 years old was used to identify sub-patches of cottonwood forest, a preferred habitat element, within larger patches of contiguous riparian forest.
To assess the accuracy of the habitat model, cuckoo observation data collected from 1987-1990 were compared to the study's 1987 modeled sub-patches.
To augment the existing cuckoo habitat areas, opportunities to expand the zone of cuckoo habitat formation examined the Sacramento River channel downstream of RM 145 in the Sacramento Valley.
Results/Conclusions
Between 1952 and 1987 there was a 16% loss in total riparian vegetation and an 11% reduction in cuckoo habitat. The habitat analysis indicated only 15% of the habitat sub-patches identified in 1952 were spatially coincident with those in 1987 and 27% of the sub-patches delineated for 1987 emerged anew and independently of the 1952 patches; the remaining 83% formed by shifting adjacent to the patches from 1952. These findings suggest that conservation of channel meander dynamics is critical to the recovery of the cuckoo.
The comparison of observation data to the study's modeled patches indicate 79% of the modeled sub-patches correctly predicted cuckoo presence or absence. The commission and omission errors were 7% and 14%, respectively.
The best opportunity to expand the cuckoo habitat recovery zone is levee setback from RM 84-145 on the Sacramento River.