April 2006
By Suzie Fork
Caspian Tern colony
Since 2000 Caspian Terns have been monitored on two islands of South Marsh, recording number of adults present and timing of reproductive events (presence of chicks, fledging success). Threats to the colony include predation (e.g. raccoons) as well as potentially the pesticide DDT, which has been detected in the slough’s mud. Overall, the use of the islands by the terns for breeding has been highly variable. In 2001 and 2002 reproduction appeared to be highly successful, with at least 80 fledglings observed (or estimated) each year. By contrast, in 2005, no adults were seen using the islands for breeding.
Heron, egret, and cormorant rookery
From March to August volunteer observers record the courtship, nesting, and fledgling activity of herons, egrets, and cormorants using pine trees adjacent to the rookery ponds. The overall goal of this program is to track the use of the rookery by these three species over time and document any changes in reproductive timing. The damage to the trees, used by the nesting birds, is also assessed. Since beginning the monitoring program in 2000, numbers of herons and egrets have remained steady, while cormorant numbers continue to increase. In 2005 the birds began nesting in a new area after a strong wind event killed large egret and heron chicks.
Chickadee nestboxes
Each spring since 1997 volunteers have tracked the use of about 150 manmade nestboxes found in the oak woodlands of the Reserve by Chestnut-backed Chickadees and Oak Titmouse. Nestbox occupancy (which species uses the boxes), indicators of reproductive success (hatching and fledging success), and timing of events are recorded for each nest. Close inspection of the previously occupied nests also reveals whether the nestlings are parasitized by blowfly larvae. Monitoring these parameters may be helpful in assessing the health of the oak woodlands potentially related to Sudden Oak Death, global warming, etc. Overall the nestboxes have a high occupancy rate, mostly by Chestnut-backed Chickadees and high fledging success as well as no parasitism (since beginning this observation in 2000). 2004 and 2005, however, had high nestling mortality of undetermined cause.
Breeding Raptors
From January to August volunteer observers follow all nests found at ESNERR, both those that are located in constructed boxes as well as natural nest sites. The goal of this program, which began in 2001, is to document the use of the Reserve by breeding raptors, particularly by the potentially vulnerable White-tailed Kite populations. Other species found breeding here include Barn Owls, Great-horned Owls, Red-shouldered Hawks, and American Kestrels. In 2005 the numbers of breeding raptor pairs in included: White-tailed Kites (3 pairs), American Kestrel (1 pair), Red-tailed Hawk (1 pair), Great-horned Owl (2 pairs), and Barn Owls (4 pairs).
Migratory Shorebirds
Beginning in 2003 surveys have been conducted twice in fall (and two additional surveys will be added this spring), to count shorebirds, waterbirds, and waterfowl at five different sites around Elkhorn Slough. Three sites are located at ESNERR (North Marsh, South Marsh, and Parsons Slough) and two others are nearby (North Harbor and the main channel of Elkhorn Slough). The overall goal is to track bird use of wetland habitats and compare to data from MLML students in the 70s and 90s. Also by contributing to regional surveys it might be possible to determine whether any changes are regional or local. Another goal is to see whether there are correlations with erosion rates and bird usage. MLML student Sarah Connors found an increase in density that she attributed to habitat loss from erosion. She also discovered that shallow lagoons with muted tidal flow are particularly valuable to these birds. The four annual spring/fall surveys will continue what Sarah’s work initiated. Since 2003, fall abundance of birds in the main channel has been as high as nearly 17,000 birds (mostly shorebirds and gulls) while North Harbor and North Marsh each have had over 2000 birds counted during at least one of the fall surveys. In terms of the number of species, up to 35 species were counted in the main channel during fall while greater than 25 species were observed at North Marsh and North Harbor during at least one of the surveys.
Reserve Shorebirds
Since 2000 monthly shorebird, waterbird, and waterfowl surveys have been carried out at various freshwater and saltwater sites along the South Marsh loop trail. These sites include: the two freshwater ponds below the barns, the salt pannes on either side of the causeway just adjacent to the Reserve Bridge, as well as the fresh and salt water areas on either side of the rookery berm. Like the migratory shorebird monitoring program, the goal of the Reserve shorebird survey is to track bird use of the wetland habitats. If dramatic differences are detected in the abundance or diversity of birds, further investigation will attempt to reveal whether this is a local or regional phenomenon. Interestingly, species with significant difference in abundances from the period 2002 - 2005, for example, include cormorants (most abundant in 2004) and waterfowl (higher abundances in 2002 and 2005 than in 2003 and 2004).
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