Monday, September 24, 2012

Lighthouses and Migrants

For the first few decades that PRBO worked on the Farallones, a powerful rotating light on the lighthouse acted as a beacon to lost ships, birds, and bats.  An analysis of 38 years of hoary bat arrivals on the island revealed that nights during the dark phases of the moon had a greater likelihood of bats being detected in the trees the following day than bright phases of the moon (Cryan & Brown, 2007, Biological Conservation).  The authors theorized that the darker nights increased the probability that these migrating bats would see and be attracted to the lighthouse.  And in fact, there are several accounts by previous biologists of bats circling the lighthouse during dark nights. At the time of the published paper, island biologists were finding bats on average >7 days per fall.  However, since the powerful rotating beam on the lighthouse was switched to a weaker, pulsating light, the number of hoary bat arrivals to the island has plummeted to approximately one per fall.  What effect, if any, this lighthouse switch has had on bird arrivals to the island is unknown, but it does seem that fewer birds are finding the island at night, with most birds arriving during the day.

The 16th through the 18th brought low winds and high overcast skies, which meant that good numbers of migrant birds descended upon the island. On the 16th we banded our first Yellow-rumped Warbler of the fall as well as our second Baltimore Oriole of the season; interestingly we have yet to record a Bullock's Oriole for the fall, which is normally our most common oriole. In addition, we had 11 species of warbler including a Black-and-white Warbler, 2 Chestnut-sided Warblers, a new Magnolia Warbler, and 3 Blackpoll Warblers. We also spotted a Vaux's Swift zipping past the lighthouse.

On the Farallones, we color-band six songbird species, including this Townsend's Warbler.  Each individual bird gets a unique color combination, which allows us to identify individual birds in the field without recapturing them, so that we can keep track of how many birds of our most common species are on the island each day.

The 17th brought us more migrants including a mixed flock of six teal, 3 Blue-winged Teal and 3 Cinnamon Teal. The Cinnamon were the first in over a decade, while the Blue-wings represented the 11th, 12th, and 13th records for the island and an island high count. Immatures and females of these two species are very similar in appearance, but lucky for us, they circled close to the island a few times, and we were able to get some good photos to aid in identifying them. The primary features to distinguish them are bill size (longer and spatulate in Cinnamon) and facial plumage (distinct white wrapping around the underside of the bill in Blue-winged). Can you figure out which are which?   The day continued with the first Vesper Sparrow of the Fall, a male Indigo Bunting, a male Dickcissel, and a Bobolink. We also added to the warbler count with 2 MacGillivray's Warblers, a Wilson's Warbler, and a Tennessee Warbler.

The 18th continued to be calm and cloudy and added several new migrants to the many birds still refueling from the previous two days. Notable arrivals for the day included a Willow Flycatcher, a Hammond's Flycatcher, the first Hermit Thrushes of the fall, a Painted Bunting, and 3 more species of Warbler including Blackburnian Warbler and Bay-Breasted Warbler - all and all a pretty nice little wave. We ended up seeing 17 species of Warbler over the 3-day wave. Although the last few days have been windy, with thick fog the past two days, we're hopeful that conditions will improve in the near future so we can catch another wave. 

In addition to studying the flying migrants, we conduct daily surveys from the lighthouse to document the occurrence of white sharks around the island as they fuel up each fall for their annual migration to the middle of the Pacific, where breeding is thought to occur.  The Farallones is the only places in California where white shark attacks can be routinely viewed. A recent analysis of shark genetics and transmitter data has revealed that the population in the northeastern Pacific (the ones we see in California) is genetically and geographically isolated from the other populations around the world (Jorgensen et al., 2009, Proc. Roy. Soc).  Furthermore, using underwater videography to identify individuals has led researchers to believe that this population is extremely low, possibly less than 400 adults (Chapple et al., 2011, Mar. Bio.).  For this reason, there is a push amongst conservation groups to get this population listed as federally threatened or endangered.  Over the past several years, the numbers of attacks at the Farallones has been steadily declining, so the seven attacks we have witnessed thus far during September have been a welcomed turn of events.

While looking for sharks, we also document the number of cetaceans within sight. For the first two weeks of September, we were seeing three resident Gray Whales that spend their time foraging around the island, but lately a fourth may have joined the group. After spending hours watching them cruise around during shark watch, we have become pretty familiar with each individual and have given them names so we can discuss which ones we are seeing. The two in this photo are affectionately known as Big Moby (in the back) and Lil' Moby (in the front). The third resident, Big Spot, is one that we have been seeing for at least the past three years. The fourth individual is also small and has quite a bit of red on its forehead. Its name is less settled, but has been referred to as Red Face or Lil' Red.

Tune in next week for more excitement.

Saturday, September 15, 2012

The Waves Keep Rolling In

 Migration usually happens in waves and is not just one steady phenomenon.  These waves tend to follow the weather patterns as high and low pressure systems slide past from west to east.  Interestingly, on the East Coast fall migration tends to pick up after a low pressure system passes because lows spin counter-clockwise, which create north winds in their wake that act as a tailwind.  This probably also happens on the West Coast, but on the Farallones, bird waves usually arrive just as a weak low passes to our north.  This tends to create the ideal weather pattern for us - light southeast winds and high overcast skies.  The theory is that the birds heading south along the coast are flying above the cloud deck and thus don't realize that they are getting blown slightly off course and out over the open ocean.  At dawn, when they fly down through the clouds for food and shelter, they then realize that they are over the open ocean.  If the the height of the cloud ceiling is low enough so that the mainland is not visible (where the birds would rather be), but high enough so that the birds within 10-15 miles can find the islands, a nice fallout can occur.

Since our last post on 3 September, the bird migration has picked up significantly.  The 4th started out with fog, light winds, and only a few miles of visibility.  The poor visibility kept many birds from finding the island, but we did find one arrival that was quite unexpected, a Red Crossbill.  Although there are 57 previous records, the last time that one was seen on the island was in 1998.  The reason for this long gap in occurrence is because they are an irruptive migrant, meaning that they are driven south in large numbers in some years due to a scarcity of food on their breeding grounds.  As you can see from the photo, the bird is not red, but yellow - only the males are red in this species. 

This bird lasted long enough for us all to run outside and photograph it.  As soon as we opened up the mistnets to attempt a capture, it flew off to the north, and we did not see it again that day.

The weather on the following day, the 5th, was nearly perfect for a fallout, with light winds out of the southwest, cloudy skies, and only 10 miles of visibility.  I walked up to the lighthouse to start my shark watch full of expectation, not for sharks though, but birds for the top of lighthouse hill is where most wayward migrants first touch down. As I headed up, I could see a few warblers sallying off the lighthouse for insects, a sure sign that a fallout was happening.  When I got to the top, I found six species of warbler: Yellow, Townsend's, Hermit, Black-throated Gray, Chestnut-sided, and Wilson's.

Shortly after my arrival on the lighthouse, I noticed that there was another female crossbill on the lighthouse.  Since we hadn't banded the one the day before, I was uncertain whether this was the same bird.

However, it sure seemed that the other bird had departed the island.  Without proof, though, we would have to consider it the same bird since there were no intervening days between the observations.  Several days later, I was looking at my photos and noticed that the primaries (outer most feathers on the wing) showed considerably different amounts of wear.  The crossbill on the first day had extremely frayed tips to its primaries,whereas the crossbill on the second day had intact primaries with just a few nicks.

In addition to the above birds, we also found a few sparrows in the genus Spizella, such as Chipping, Clay-colored, and Brewer's.  During the fall, these birds are notoriously difficult to separate from one another, and for some reason on the Farallones, we always seem to get birds that are on the fringe of what is considered "normal" for a species.  On this day we found a Chipping Sparrow, normally very easy to identify, that we initially mistook for a Clay-colored.  The Clay-colored features that it has are the mostly gray nape, relatively strong lines bordering the throat, and general buffy coloration to the mantle and throat.  The features in favor of Chipping, though, were more definitive, such as the blackish line bisecting the eyering and running through the lores, a poorly defined median crown stripe, long wing (2 mm longer than Clay-colored), and gray rump (not visible in this photo).  Could this be a hybrid Chipping x Clay-colored?  Probably not, but only its parents will ever know for sure.

We also found a tricky Brewer's Sparrow.  This species is usually fairly easy to distinguish from Chipping and Clay-colored Sparrows because Brewer's have a full white eyering.  This one, though, had a dingy grayish-brown eyering.  We identified this as a Brewer's through a process of elimination.  It could not be Chipping because it did not have black line through its lores and the rump was brown.  Separating it from Clay-colored was more difficult, but it did not have a distinct median crown stripe, the stripes bordering the throat were fairly weak, and the general coloration was cold, grayish-brown, not the warm, buffy brown usually associated with Clay-colored.  Unfortunately, all the measurements were intermediate between Clay-colored and Brewer's.  What species do you think this is?

The 6th of September was fairly calm, but unfortunately the mainland was clearly visible.  The highlight for the day was a Black-throated Sparrow.  Juveniles of this species are frequently misidentified as Sage Sparrows, but notice the full white supercilium.

September 7th was calm again, but the mainland was still clearly visible.  A few arrivals showed up, including an adult male Cape May Warbler.

The winds were blowing strongly out of the northwest on September 8th and the visibility was good enough for most birds that found themselves over the ocean to continue back to the mainland.  But a Painted Bunting decided the island was as good a place as any and cheered the islanders who saw it.

The 9th through the 11th were mostly clear, with strong to moderate northwest winds resulting in only a few arrivals.  This lull between the waves allows to birds to depart and continue south.  The only notable arrivals this period were a Yellow-headed Blackbird and a Baltimore Oriole.

The next wave began on the 12th, when we were greeted with overcast skies, 6 miles of visibility, and light southeast winds.  Warblers of eleven different species started filtering out of the sky about an hour after dawn, with a Bay-breasted, a Blackburnian, and an American Redstart leading the way and making quick friends. Multi-species flocks, with similar feeding styles, often band together during migration and on their winter grounds to help each other watch out for danger.

Several western migrants were present in the morning too including Wilson's and Hermit.

A few more eastern migrants arrived later in the morning to make for a great little wave.

While we all enjoying this bonanza of warblers, a posse of birders was bobbing around in Mirounga Bay off Saddle Rock hoping that the Northern Gannet would arrive.  Unfortunately for them, they arrived at noon, which was 3.5 hours before the bird arrived.  Thankfully they persevered, and we were able to get them on it as soon as it arrived.

The following day, September 13th, dawned foggy and calm, with few birds around, so we had a Waffle Morning.  The fog lifted after lunch and a few birds began arriving.  As Dan was walking to up to the lighthouse, he suddenly heard the distinctive "jip-jip" call of another Red Crossbill.  This one landed on Lighthouse Hill.  There are several "types" of Red Crossbills that breed in different regions, and each type has a unique sounding call.  We recorded this bird's calls in hopes of figuring out which type it is and where it came from.

The wave continued for one last day on the September  14th.  While eating my Trader Joe's O's, I received a phone call from ex-intern Matt Brady that there was a Yellow-throated Warbler on the lighthouse that he had seen with the webcam.  We all headed up the hill and sure enough, the island's 6th occurrence of a Yellow-throated Warbler was up there. This species breeds in the southeastern United States and is a very rare visitor to California.  In fact, the first record for California was only in 1969, and that record occurred right here on this very island.

When will the next wave happen?  Stay tuned to find out.

Monday, September 03, 2012

Another Fogged-in Day On The Farallones

Our 2012 Fall crew is just getting settled in here on Southeast Farallon Island.  After two weeks, September has arrived, and so have lots of migrating landbirds, shorebirds, and even our first shark attack of the fall!

As you might have guessed, we have had some fairly foggy weather up to this point, (socked in all day today) but hopes are high for better visibility, calmer winds, and better conditions in general for migrant birds to find our island.

These first few weeks have already turned up some great records.  The Ruff that you saw in our last post was only the first of some great observations including a Semipalmated Sandpiper, Yellow-bellied Flycatcher, and Hooded Oriole.

Over the next three months, we will be conducting surveys every day to monitor migrating seabirds, landbirds, shorebirds, pinnipeds, cetaceans, bats, white sharks, and even salamanders.  Stay tuned to see what we will find!

Here are some photos of birds we have seen over the past week.

This juvenile Ash-throated flycatcher looks a lot brighter than you would expect in an adult.  As you can see, nearly all of its flight feathers are a rich rufous, whereas an adult would show darker grayish secondaries.
During a daily gull survey, Jim noticed this California Gull which was banded this year at the Mono Lake gull colony.

The biggest rock star on the Farallones right now is certainly the Northern Gannet.  Many birders have been taking whale watching tours out of San Francisco just for a chance to see this incredible bird which was first spotted on April 25.  

We spend long hours counting all of the Black Turnstones roosting at high tide, so it's always a pleasant surprise when we run across a Ruddy Turnstone like this one.

Yellow-bellied Flycatcher is an especially rare bird in California, however, 9 of the 24 accepted state records have occurred here on SEFI.
With flycatchers in the genus Empidonax, like this Yellow-bellied Flycatcher, measurements of a bird in the hand must  often be taken in order to confirm the bird's identification.  This species is very similar to the much more common Pacific-slope Flycatcher, but after capturing, banding, and measuring this individual, there was no doubt that it was a Yellow-bellied.
Here's a Pacific-slope Flycatcher from the same day for comparison.  Note the dull edging on this bird's tertials, and the teardrop shaped eye ring.  The Yellow-bellied has much brighter white tertial edging and a rounded eye ring.

Western Sandpipers can be tricky to separate from Semipalmated Sandpipers, unless of course they are posing only inches apart, "crossing swords".  Note the much longer, decurved bill of the Western on the left, compared with the short, straight bill of the Semipalmated on the right.