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Archive for the ‘Passerine Migration’ Category

Yesterday (October 17) marked our official last day of fall banding here at Petit Manan Point, and though we’re sad to be done we’re also happy to have had such a productive season, collecting data on over 2200 individual birds.  As we mentioned in our first blog post, the data amassed each season helps shape management strategies and allows for a better understanding of bird population trends.  As an example, the alarming decline in Rusty Blackbird numbers (approximately 90% since the mid-twentieth century) was discovered via formal survey techniques including breeding bird surveys and banding data.

It seems fitting to conclude this season’s blog with a photo of a young male Rusty Blackbird caught here on October 13.  Among other challenges, habitat loss has played a large role in the precipitous decline of this and many other species, underscoring the importance of public lands like wildlife refuges in maintaining and enhancing vital ecosystems across the country.

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This season’s banding crew (left to right): Jeff Moker, Lauren Morgan-Outhisack & Jordan Chalfant.

 

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Last Monday (October 8) we captured a total of 30 different species here at Petit Manan Point.  This amounts to roughly 4% of the total number of breeding species in North America.  It may not seem like a lot, but it is: it translates into vast numbers of individual birds utilizing refuge habitat on their migratory journey.

Below are some highlights from the past week:

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White-eyed Vireo
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Black-billed Cuckoo
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Chestnut-sided Warbler
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Gray Catbird
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Pine Warbler
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Savannah Sparrow

Tennessee Warbler

“Yellow” Palm Warbler

Yellow-breasted Chat

 

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It is hard to believe it’s already October, but we might have guessed by the number of Myrtle Warblers moving through.  Since the calendar flipped we have caught 142 Myrtles, making up over 55% of the total of newly banded birds in the last 3 days.  As we noted in our last post, these birds can winter at fairly high latitudes owing to a specialized digestive tract that allows them to eat berries that are inedible to most other species.  They are also interesting in that they are 1 of only 6 warblers that breed in North America that undergo marked changes in plumage aspect from season-to-season.  Pictured below are a young female (L) and adult male, both in non-breeding or ‘basic’ plumage.

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Fortunately for us, ageing Myrtle Warblers is fairly straightforward, as this species tends to show obvious molt-limits.  Molt-limits are simply differences in the appearance and structure of feathers due to the different times at which they were grown.  In the wing-spread of the Myrtle Warbler below, the difference between the recently molted, fresh alula covert versus the pale middle alula indicates that this is a young bird…

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…and the lack of a difference between the same feathers on a different bird below indicates that this is an adult (this is the wingspread of the adult male pictured alongside the female in the first photo above).

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Speaking of molt-limits, Red-eyed Vireos can show some pretty dramatic differences between feather generations as well.  Below is a young bird that had a rather limited molt compared with most of the other vireos we have processed.  Note the retained outer greater coverts – most of the hatch year individuals we have seen have molted these completely.  The Red-eyed Vireo is noted for producing multiple clutches per season, so it may be that this individual hatched later in the summer and did not have time to molt as extensively as birds that hatched earlier.

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In addition to the increasing numbers of Myrtle Warblers, we have seen more White-throated Sparrows on the move as well.  Like Myrtle Warblers, these sparrows are relatively short-distance migrants.  They abandon boreal breeding grounds in Canada to overwinter in coastal/southern U.S., as well as northeastern Mexico.  Unlike Myrtle Warblers, there is limited dichromatism between males and females, and identifying the sex of an individual is generally impossible outside of the breeding season.  Pictured below is a young bird making its first foray south.

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We typically catch more Golden-crowned Kinglets here than their Ruby-crowned counterparts, so it was a treat to have been visited by this young male Ruby-crowned Kinglet.  This is a species that shows marked dichromatism between the sexes, as males are characterized by the eponymous red crown that is sometimes used to intimidate rival males in territorial disputes.

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And finally, a photo of Bear Cove, about 200 meters due west of our banding station.

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Being stationed on a peninsula can result in some pretty ‘birdy’ days, as migrants funnel down its length in search of food.  We’ve already banded 100 or more birds on a couple of days, and if previous years are any indication, we’ll likely be in for more during this period of ‘peak passage’.

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The sun is shining and the weather is sweet, at least for today. The sun gives us energy to run our computer and acoustic devices.  Since the acoustics get priority over the computer, we have had to wait a couple weeks for a good sunny day to fully charge our computer, thus post a blog.  It keeps us in our toes!

The past few weeks have been spectacular.  Only a few days ago, we had some surprise visitors to our banding site: 300 harbor seals! All of which were searching for food, floating around, and calling to each other.  We are so lucky to be living on such an amazing island, seeing some beautiful scenery and working with some really cool birds.  We have gone on epic adventures exploring the island and we have holed up in our sleeping bags eating PB&Js and  reading novels from action adventure, to fantasy, to hiking the Appalachian Trail and more.   Of course we are also working, trying to catch as many birds as we can.

To date we have caught over 450 birds in 32 banding days.  That’s pretty good considering we are only running 14 nets and many days we have to close early because of wind and or rain.  Over the past couple weeks we have been getting some late warbler migrants consisting mostly of Blackpoll Warblers (BLPW).    Since we have been seeing so many BLPWs we have noticed some remarkable variations in their condition.  To explain, one of the measurements that we record on all birds caught is the amount of fat they carry, fat score.  Blowing to separate the feathers we rate the amount of fat filling their furculum, a hollow at the top of the breast.  Fat appears yellow to orangish.  Most birds we have caught have a fat score from 0-1, meaning they have no fat up to fat lining the furculum’s sides.  Recently, the majority of BLPWs we catch score from 2-5.  A bird with a fat score of 5 has fat bulging from the furculum and pouring over the sides of the breast all the way down covering the abdomen!  These birds are carrying up to 25% of their body weight in fat.  The reason for so much fat is that they are gearing up for their nonstop flight to South America for the winter.

Some of the highlights that we have found in our nets are Gray Cheeked Thrush, Bicknell’s Thrush, Blue-headed Vireo, Rusty Blackbird, and Palm Warblers.  We have also been spotting Baltimore Orioles around the house.  A Brown Thrasher stopped over at our banding site yesterday, pretty cool bird if you ask me!  Cross Island is amidst the northern most portion of their range.

 

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Since our last blog post 6 days ago we’ve seen some ups and downs in the daily capture rate, but things are picking up as more and more Myrtle Warblers move through.  Our biggest day of the season thus far was last Friday (Sept. 21), when we processed 78 new birds, 57 of which were Myrtles!  This is a widespread and abundant warbler that breeds in coniferous forests and winters as far north as Massachusetts.

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Part of what enables this species to winter at such high latitudes is their ability to digest bayberry and other waxy fruits, though they still enjoy a tasty and nutritious invertebrate when available.

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We’ve also seen a moderate swell in vireo numbers over the last few days, with a nice mix of both Red-eyed and Blue-headed Vireo (below) flocking-up with other migrants.  Vireos are closely related to Shrikes, and one of the characteristics they both share is a somewhat menacing hooked bill, which aids them when feeding on fruits, invertebrates or (in the case of shrikes), small vertebrates.

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And we finally had our first Baltimore Orioles pass through this week…pictured below is a hatch-year female.

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Many passerines show similar patterns of molt, and as with the hatch-year Black-throated Blue Warbler discussed in our September 5 post, this female had a good degree of contrast between older juvenal feathers and newer, recently replaced ones.  More often than not, this indicates a young bird, as the adults undergo a complete molt and do not show marked differences in feather aspect.  Below is a closer look at the wingspread of this young female oriole.

Known as ‘molt-limits’, these differences in feathers allow bird banders to accurately assign individuals to age-classes, and one of the leading figures in understanding this phenomena is Bob Mulvihill (below, with a ‘Yellow’ Palm Warbler).  Bob’s yeoman work on molt, as well as a devotion standards rarely matched has equipped a generation of North American banders with the tools necessary to collect accurate, robust data.  It goes without saying that we were honored and delighted to have been visited by he and his wife Pam on Saturday (Sept. 22).

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Weather plays a dominant role in bird migration, and to a great degree dictates when birds will move en masse to the south or north, depending upon the season.  Since the last few days here at the refuge have been dominated by south winds and fog, we have not seen much migratory activity, given that birds moving south will tend to avoid these exhausting conditions.   The promise of a fast approaching cold-front, however, gives us reason to be optimistic.  Check out the radar signature for the northeast taken from the National Oceanic and Atmospheric Administration’s website this afternoon:

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No doubt you can make out the turbulent area in this image, but what isn’t visible in this frame and what follows the frontal boundary are northern winds – perfect if you are a bird in need of a ‘push’ to the south!  Hopefully this will translate in to some new arrivals over the next few days, as the front passes over us.

It is also worth noting that large-scale movements of birds show up  on weather radar, so the next time you are checking your local weather have a look at the radar signature for your area.  Where rain and cloud regularly appear as haphazard or curvilinear signatures, bird movement shows up as pixelated circles:

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See http://virtual.clemson.edu/groups/birdrad/COMMENT.HTM for a more thorough treatment of radar ornithology.  Very interesting stuff!

In our previous post we discussed the amazing distances some birds cover during migration, which begs the question, just how do they do it?  In large part (aside from favorable weather conditions) it comes down to burning fat.  Birds moving great distances will become ‘hyperphagic’, which means they will eat like a superbowl fan on Sunday!  But instead of sleeping off the largesse of calories on the couch, they utilize that energy to power their epic flights south.  Here is a photo of a Red-breasted Nuthatch with a deposit of fat in the furcular hollow (basically the space between the collar bones on you and I).  Hopefully you can see the contrast between the red flight muscles surrounding the yellow fat deposit.

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Finding abundant resources are a migrating bird’s stock-in-trade, and here at the refuge we are fortunate to have a large crop of blueberries at their peak, which a number of staging Whimbrels have been fattening-up on.  Whimbrels are a large shorebird whose winter range includes both coasts from the southern U.S down through South America.  Incredibly, this species has recently been found to successfully navigate their way through tropical storms and even hurricanes during their southbound flights over the Atlantic.  Though we do not band these birds, we still maintain records of their presence as a corollary to the banding effort.

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We never take for granted our beautiful surroundings.   Petit Manan Point is part of the Maine Coastal Islands National Wildlife Refuge complex that includes more than 8,000 acres of coastline and offshore islands.  Here Jeff samples a portion of this incredible area while scouting for Northern Gannets.

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Any day you find yourself working with birds is a good day, and what we learn from the birds we band can really help put life in perspective.  Pictured below is the third Blackpoll Warbler we have banded thus far, and it is a particularly notable wood-warbler in that it engages in a mammoth fall migration that can find individuals traversing the open Atlantic on their way to South American wintering grounds.  Keep in mind these are songbirds, and are unable to alight on the open ocean for a rest as are waterfowl, so they must travel nonstop on a flight that can be up to 3000 kilometres long.  This has been likened to a human running 4-minute miles for 80 hours!  The challenges these little songbirds surmount in their annual life-cycle are truly mind-boggling.

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Map courtesy of www.borealbirds.org

The aptly named Yellow Warbler is an early fall migrant, with movement to the south typically peaking in early August, so we were pleasantly surprised to find this adult male in our nets on September 3rd.

Another warbler whose name needs no explanation is the Black-throated Blue Warbler.  These gems of the eastern forests are on their way to the Bahamas and Greater Antilles for the winter.   Pictured here is a young male who hatched-out from an egg this past summer.

We can tell he is a young bird due to the differences in the wing feathers denoted below.  Adult birds will show no difference between these feathers since they undergo a more extensive molt than their hatch-year counterparts.

A warbler whose name does require some explanation is the Magnolia Warbler.  These birds typically nest in dense coniferous forests, not magnolias, but the first specimen was collected from a magnolia tree and the name has remained.  Pictured below is a male in non-breeding or ‘basic’ plumage.

We would be remiss if we did not include a photo of a very common denizen here at the refuge…we have seen quite a number of different individuals, typically out foraging at dawn and dusk.  This large individual was spotted toward the south end of the point, and was given a wide berth!

Porcupine!

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