Friday, October 09, 2015

Mono Lake Gulls on the Farallones



Most falls since 2001 I have undertaken a migration of sorts: one that takes me from Mono Lake, in eastern California where I live, to Southeast Farallon Island. This island has an in incredible draw for me – the birds, the wildlife, the magic, I keep coming back to satisfy my soul. It seems an unusual route to travel – from Sagebrush, Pinyon Pines and Clark’s Nutcrackers to crashing waves, ocean breeze, sharks and seabirds. Surprisingly, I am not alone on this voyage. Each year, large numbers of California Gulls make the same exact journey.

California Gulls hold a special place in my heart – and not just because of this commonality. Since 2005 I have run Point Blue’s Mono Lake California Gull research project, which measures the colony’s annual population size and chick production. Initiated in 1983, this is one of Point Blue’s longest continually run research projects. Back then, the future of the Mono Lake gull colony was perilously threatened by human-caused water diversions. These diversions lowered the lake level to a point where the gulls’ formally safe nesting islands became connected to the mainland, making them vulnerable to Coyotes and other land-based predators. Fortunately, due to the hard work of dedicated scientists and others, in 1994 the lake was court-mandated to be managed, through reductions in water diversions, to rise to a target surface elevation of 6392’. This elevation would keep the gull nesting areas protected and the lake ecology thriving.

Mono Lake is a terminal lake, meaning water entering through its tributary creeks can only exit via evaporation. Over time the lake became hyper-saline, much like Utah’s Great Salt Lake. In summer and fall, its briny waters contain alkali flies, trillions of brine shrimp, and the lake is home to one of the largest breeding colonies of California Gulls in the world.   

Breeding California Gulls at Mono Lake. Note the snow-capped volcanoes in the back-ground (the Mono Craters). Some of the gulls from Mono Lake migrate to Southeast Farallon Island. Photo by Justin Hite
But in fall, the California Gulls leave Mono Lake and cross the Sierra Nevada in one high-altitude flight. Most winter coastally, often traveling relatively far offshore to forage. On pelagic sea-birding trips you may continue to see California Gulls at distances further out at sea than their Western or Glaucous-winged cousins. The flexibility of California Gulls to transition from foraging on alkali flies and brine shrimp on Mono’s shores - to riding oceanic waves with shearwaters, keying in to pelagic food resources, and following oceanic upwellings in their winter pelagic transiency, I find absolutely astonishing. This Great Basin to coastal transition is especially impressive for the juveniles; as many have only gained independence from their parents and learned to forage independently at Mono Lake just a few weeks before migrating to the coast and the Farallon Islands, where they must learn a whole new set of foraging and survival skills.

California Gull chicks at Mono Lake about to be banded in temporary corrals. The structure in the background is a fake half volcano from a 1952 movie set that now serves as basecamp for Point Blue gull banding volunteers. Photo by Teague Scott
The fact that many Mono Lake California Gulls use the Farallones became apparent starting in 2009, when we began color-banding the Mono Lake gull chicks. On a single day that fall,  I had a high-count of 6 color-banded Mono Lake gulls! That translates into almost 1% of all the California Gull juveniles produced at Mono Lake that year roosting on a few acres of little Southeast Farallon Island that day!

Each year since, fall biologists and interns have detected color-banded Mono Lake gulls, although numbers fluctuate greatly each year. Considering that we only band 3 -4 % of Mono Lake’s gull chicks each year, these detections make it clear that the Gulf of the Farallones and its surrounding waters are an important stop-over for a significant proportion of Mono Lake’s California Gulls. 






Fall California Gull data from SEFI show some really interesting trends. Starting about 10 years ago, shortly after a standardized protocol for counting migrant gulls was initiated in 2006 (they were counted opportunistically before), annual numbers of migrant California Gulls visiting Southeast Farallon climbed tremendously. Their numbers peaked in 2008, and then dropped back to where they were before the climb. It’s difficult to interpret what caused this, but I suspect it relates to local food abundance. When feeding is hot around the Farallon Islands, the California Gulls will come, if it’s better elsewhere, they will move elsewhere. Color band resights and band recoveries of Mono Lake California Gulls on fall migration have also been difficult to interpret as well: some birds have been resighted north as far as Oregon, while others go south (southern California or Baja) – even within the same fall. Much is unknown about California Gull fall and winter movement patterns: where they go, how much they wander, what they eat, and their habitat requirements. But, hands-down, the single place where by far the largest number of Mono Lake color-banded gulls have been resighted is right here on Southeast Farallon.

 
Color banded juvenile California Gulls banded at Mono Lake, photographed on Southeast Farallon. The red coded bands are great – easy to detect, frequently reported by observers, but also very expensive. At Mono Lake, some chicks get the red, coded bands (as many as we can afford) that allow us to quantify and track individuals, but most get a simple color band, like the green one below. Photos Jim Tietz

Hopefully fall biologists and interns continue to document many color-banded Mono Lake gulls on the Farallones. Yet drought and climate change are bringing back the same predation threat caused by low lake levels we thought was resolved following the State Water Board’s 1994 decision to “save” Mono Lake. Despite reduced water diversions, it is currently about 14 vertical feet below the targeted 6392’, and dropping. Just one more dry winter could result in large parts of the gull colony becoming accessible to coyotes, which would be devastating. This was not supposed to happen. But data and models used to generate allowable water diversion rates back then did not include climate science as we know it today. There are measures in place to reduce or eliminate water diversions from Mono Lake if it continues to drop, but there’s a chance these rules are not fully adequate to protect the gulls in a hot, dry climate.  Hopefully we don’t need to resort to desperate measures to protect Mono Lake gulls, like erecting an electric fence to prevent coyotes from crossing a land bridge if the lake continues dropping. And hopefully this drought ends and Mono Lake starts a steady climb in surface elevation. But if not, science may need to step in again, as it did decades ago, to reevaluate how best to keep Mono Lake and its gulls protected.
The fog is lifting, I think I’ll take the scope out and check the roosting gulls in hopes of finding a color banded friend from Mono Lake.  

Photo from Mono Lake gull banding basecamp, overlooking Mono Lake, Paoha Island, and the Sierra Nevada. Islands of Mono Lake are home to one of the largest breeding colonies of California Gulls in the world. Photo by Ryan Spaulding
Mono Lake never ceases to amaze me. Many of the California Gulls that visit SEFI in fall were hatched here. Photo by Robert Di Paolo.
Posted by Kristie Nelson, Mono Lake California Gull Project Manager

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