Colony connectivity of Pacific Coast double‐crested cormorants based on post‐breeding dispersal from the region's largest colony

Abstract

To reduce conflicts with fish resources, other colonial waterbirds, and damage to habitats, double‐crested cormorants (Phalacrocorax auritus) are currently controlled (lethally and non‐lethally) throughout much of their range. Concerns are growing over the Pacific Coast's largest double‐crested cormorant colony at East Sand Island (ESI), Oregon near the mouth of the Columbia River, where cormorants forage on juvenile salmonids, many of which are listed under the United States Endangered Species Act. Management of this colony is currently under consideration and may call for a redistribution of a portion of this colony numbering more than 12,000 breeding pairs in 2009. We investigated regional and site‐specific connectivity of ESI cormorants using satellite‐telemetry to track post‐breeding dispersal. Cormorants dispersed widely west of the Cascade‐Sierra Nevada Mountains from British Columbia, Canada to northern Mexico. Tracking data demonstrated direct connectivity between the double‐crested cormorant colony at ESI and nesting sites throughout the dispersal area. Results of this study indicate that some cormorants from ESI could disperse to prospect for nesting sites throughout much of the western portion of the range of the Western Population; however, regional variation in connectivity with the ESI population, distance from ESI, and site‐specific nesting history will likely result in variable prospecting rates among regions and sub‐regions. Management efforts aimed at redistributing ESI cormorants across western North America (e.g., social attraction or dissuasion techniques) might be best allocated to areas or sites known to be used by tagged cormorants, particularly those sites with an established nesting history. © 2012 The Wildlife Society.

The spatial scale of time‐lagged population synchrony increases with species dispersal distance

“…However, the tendency for mark–recapture studies to underestimate dispersal distances has been established in previous studies (Koenig, Van Vuren, & Hooge, ; Schneider, ; Yamamura, Kishita, Arakaki, Kawamura, & Sadoyama, ). Additionally, we found a number of telemetry studies that reported mean bird dispersal distances much larger (50–533 km; Aebischer, Nyffeler, & Arlettaz, ; Courtot et al, ; Ferrer, ; Muriel, Morandini, Ferrer, & Balbontín, ; Rahman, Batbayar, Purev‐Ochir, Etheridge, & Dixon, ) than the largest mean distance (of 25. 8 km) estimated by Paradis et al ().…”

The Salton Sea: Critical Migratory Stopover Habitat for Caspian Terns (Hydroprogne caspia) in the North American Pacific Flyway

“…Fall, winter, and spring surveys have documented flyway-significant aggregations of these species during the non-breeding portion of the annual cycle, as well as other migratory piscivorous species, including Ringbilled Gulls (Larus delawarensis), California Gulls, Herring Gulls (L. argentatus), Black Terns (Childonias niger), Forster's Terns (Sterna forsteri), and Black Skimmers (Shuford et al 2002). The ubiquitous use of the Salton Sea by Caspian Terns from two colonies (> 95% of all tracked individuals) documented in this study is remarkable for a population migrating moderate or long distances (e.g., ≥ 1,500 km) within the Pacific Flyway (Courtot et al 2012).…”

“…A majority of Pacific Flyway terns also stopover for a short period during the spring pre-breeding northward migration, while a small minority overwinter there. Other piscivorous waterbirds, including Double-crested Cormorants (Courtot et al 2012) and American White Pelicans (Pelecanus erythrorhynchos), migrating from distant breeding locations have also been documented to use the Salton Sea as a migratory stopover or overwintering location. Fall, winter, and spring surveys have documented flyway-significant aggregations of these species during the non-breeding portion of the annual cycle, as well as other migratory piscivorous species, including Ringbilled Gulls (Larus delawarensis), California Gulls, Herring Gulls (L. argentatus), Black Terns (Childonias niger), Forster's Terns (Sterna forsteri), and Black Skimmers (Shuford et al 2002).…”

Developing nondestructive techniques for managing conflicts between fisheries and double-crested cormorant colonies

“…This study addressed the question of whether cormorants will use artificial colonies, but determining where these colonies should be placed is also important. Cormorants from the East Sand Island colony may prospect for nesting sites hundreds of kilometers from the Columbia River estuary because postbreeding double‐crested cormorants from East Sand Island disperse as far as 530 km from the colony (Courtot et al ). Based on maximum foraging distances of double‐crested cormorants reported by previous studies (Neuman et al , Anderson et al , Coleman et al ), alternative colony sites should be ≥50 km from sites where fish species of special concern are susceptible to cormorant predation.…”