Wednesday, June 12, 2013

A Tern for the Worse : Predators

A flock of endangered Least Terns headlines globally last week when they returned to breed on the sandy shores of the Malibu Lagoon, as reported here first on the 411, but quickly left after crows or herons preyed on their eggs.

The diminutive “least terns,” so named because they are the smallest tern species, frequently inhabit the lagoon during the winter, says Suzanne Goode, a senior environmental scientist with California State Parks, but seeing them breed was something different.

“They feed in the lagoon and in the ocean, fly around, it’s just that they’ve never laid any eggs here since 1940,” Goode said. “The basic problem these  birds like to be on the sandy beach, and that’s where all the people like to be.” 

It’s unclear why the birds came to Malibu to breed after all this time, although Goode said there are theories.  "The Least Terns may have been lured by the ample fish populations in the Lagoon. The birds appear to come from the colony in Venice."

“They [could have experienced] heavy predation at Venice,” Goode said. “Number two, we fenced in a bigger enclosure this time [intended for snowy plovers, another bird]... another factor might be that the topography is much more open now [after the Malibu Lagoon Restoration Project], they like places with NOT a lot of shrubs around.”
“We had 58 birds here [last week], but only seven nests,” Goode said. “There were only seven nests to defend. Obviously if they haven’t laid their nests yet there’s nothing for them to defend, so they need to have about 30-35 nests before they can effectively fight off the crows.
According to Goode, after just completing  a walk thru of the nesting area with Nora Cook, they found six predated eggs. There we're tracks of American Crows adjacent to all and tracks of gulls, and medium sized herons (BCNH, SNEG) next to most and one set of GBHE/GREG tracks. The nest depressions were either intact or wind blown and were not over washed or disturbed by humans. Fears of Large surf and high tides sweeping through the nesting site was a concern but such forces did not impact  the site .The fenced area was overwashed at both the west and east ends.

There were 5+ sets of human tracks in the enclosure, 4 appear to go in/out as if retrieving something. One set does go along the rear wrack line and probably within 5 -10 ft of the nesting area. There is an area on the east end with multiple tracks that appear to go in and look at a dead gull There is one fresh set of dog tracks that appeared to enter from the east end and move along the fence, but did not go into the colony.

Upon further assessment, Goode established that a predator, most likely a crow, but possibly a heron found the colony and predated the nests

We’re going to leave the fence up here for a couple more weeks to see what happens, fence left up for snowy plover,” Goode said. “They could decide to come back here.”

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