PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 154, Fall 2008: Notes From The Field

Notes From The Field




  

Stop-over Site on a Migratory Flyway

Farallon Fall Landbirds

Jim Tietz


 
Documenting Ocean Life
CEO's Column
Farallon Landbird Migrants
Curlew Search
Seabird Aware Education
Investing in PRBO's Future
Focus: Bird-A-Thon
PRBO Highlights
Staff Migrations
 


In the fall, dawn on the Farallones can mean many new songbird arrivals. PRBO photo by Derek Lee.
The air was nearly calm and the sky was overcast as I stepped out of the house to collect the dawn weather data on September 14th. Local weather is the primary factor that determines whether migrant birds will stop for a visit out on the Farallon Islands. Conditions were promising, but it was still too dark to see whether a bird fallout had occurred. Visibility is another important factor influencing whether birds visit. When I walked to North Landing, I could barely see the lighthouse on Point Reyes--nearly ideal! On my way back to our house, I started hearing the distinctive "zeet" flight calls of Yellow Warblers exploring the island for food.

I dashed inside and woke the others to let them know that this was going to be a good day. I then climbed the path up the steep, crumbling granite slope to the top of Lighthouse Hill to conduct the daily pelican survey and start a shark watch. On bird "wave days," the lighthouse is where many of the migrants first show up. Today was no exception: dozens of warblers and flycatchers were sallying off the lighthouse for kelp flies and butterflies.
As part of PRBO's migration monitoring on the Farallones, Jim Tietz inspects a visiting warbler, a Norther Parula

Many common West Coast birds were present, including Yellow and Townsend's warblers. I was elated to spot a little gray bird with yellow wing patches hopping on the ground around the corner of the lighthouse: a Golden-winged Warbler, a rare and declining species that breeds in northeastern North America. Birds from all over the continent were arriving, and we ended the day with a spectacular list: 103 species of migrants, including 21 warbler species.

Every year since 1967, PRBO (in cooperation with U.S. Fish and Wildlife Service) has conducted surveys of fall migrant landbirds in an attempt to understand their stopover ecology, migratory behavior, and population trends. Because the island is small enough that a few people can cover the entire area, we are able to produce an approximate census of each species that we call a "daily estimated total."


"Migratory flyways are systems that are delicately interlinked by stopover sites where birds can find shelter for resting and food for refueling."

In order to understand seasonal abundance of species and migratory behavior, we need to know the duration of birds' stop-overs on the island. To help us keep track of individuals, we capture as many birds as we can in mist-nets and uniquely identify them with numbered bands. For species that are more abundant, we improve our ability to monitor their presence by applying unique color-band combinations to individuals of the six most frequently caught species --Yellow Warbler, Townsend's Warbler, Yellow-rumped Warbler, White-crowned Sparrow, Golden-crowned Sparrow, and Dark-eyed Junco.

After two weeks of a steady migration wave this September, we had banded 263 individuals of 33 species: 50 of these were Yellow Warblers and 35 were Townsend's Warblers. Later in the "big wave" day, while I was conducting an area search, a Yellow Warbler hopped into view atop a sprawling Monterey pine (one of only four trees on the island). I quickly raised my binoculars and read its color-bands--silver on the left leg and mauve over green over white on the right leg. In my notebook, I scribbled S/MGW. Back at the house, I noted that this bird was banded four days prior but only resighted on one of the intervening days. Without the precise identification tool of color bands, it would have been much more difficult to determine how long this bird was stopping over.

After two weeks of a steady migration wave this September, we had banded 263 individuals of 33 species: 50 of these were Yellow Warblers and 35 were Townsend's Warblers. Later in the "big wave" day, while I was conducting an area search, a Yellow Warbler hopped into view atop a sprawling Monterey pine (one of only four trees on the island). I quickly raised my binoculars and read its color-bands--silver on the left leg and mauve over green over white on the right leg. In my notebook, I scribbled S/MGW. Back at the house, I noted that this bird was banded four days prior but only resighted on one of the intervening days. Without the precise identification tool of color bands, it would have been much more difficult to determine how long this bird was stopping over.

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