Off to Brazil

I'm off to Brazil for three weeks to band shorebirds.  I'll post photos and stories when I return.

Take care, and happy birding –

Luke

WEWA at Palo

Worm-eating Warbler, PRBO Palomarin Field Station, Bolinas, CA 6/10/12 [Photo by Mike Krzywicki]

On June 10, the banding interns at the Palomarin field station caught this awesome Worm-eating Warbler!  Just thought I should share it.  There has also been a Black-and-white Warbler hanging around.  Wish I was still there to experience this rare vagrant.  The last time this species was captured at Palo was in 1979.  Thanks, Mike and Laura for banding and sharing this cool bird!

The Fortescue Feeding Frenzy

Red Knots, Dunlin, Sanderling, Semipalmated Sandpiper, Short-billed Dowitcher, Laughing Gull, etc.  See if you can pick out all these species.

Thursday and Friday this week we were woosh-netting and mist-netting at Fortescue Beach along the Delaware Bay Shore, a great spot to see the horseshoe crabs spawning and the shorebirds feeding on their fat-rich eggs.  One of the main parts of my job is taking blood from the shorebirds we catch.  The blood is then used to detect what the birds are feeding on.  Horseshoe crab eggs have a stable isotope signal that is different from that of other prey items (e.g. polychaete worms) and is detectable in the blood.  The birds at Fortescue are undoubtably feeding almost entirely on horseshoe crab eggs, and that is why we see thousands of birds there while the crabs spawn.  We had a good amount of luck there those two days, catching close to 200 birds total.  Here are some photos of the beautiful masses of shorebirds you can see there.

Red Knots, Dunlin, Sanderling, Short-billed Dowitcher, and Laughing Gull

More of the same

Dunlin and Semis (Semipalmated Sandpipers) coming in for a landing

Red-shouldered Hawk Indeed: Gawk at this Hawk

Three days ago we had a post about one of the two Red-shouldered Hawks we caught this past week.  The second hawk, to us banding amateurs with little hand-hawk experience, looked odd especially compared to the first bird we caught (read first RSHA post).  It had features that reminded us easterners of Broad-winged Hawk.  Look at the photos here and see what we mean.  Turns out, after running it by the hawk banders at Golden Gate Raptor Observatory, the bird is definitely within the normal range of variation seen in the California Race of Red-shouldered Hawk, Buteo lineatus elegans.  Here are some photos taken by Dan Lipp of the overzealous Frenchie holding this beautiful SY RSHA.  

This photo shows the pale grayish brown eye that is typical of a young Red-shouldered Hawk.

An adult California Red-shouldered Hawk would show a nearly solid orange breast with an orange belly with white barring. The brownish barring on this SY RSHA is very reminiscent of a Broad-winged Hawk, and it has a much smaller, streaky bib than our previous SY RSHA. However, this RSHA's plumage is within the normal variation one could expect to see within the California subspecies.

Here you can see the tail with fewer, thicker bands than our first Red-shouldered Hawk, but the California subspecies immature can show a more adult-like tail than the eastern subspecies. 

By Luke Musher and Cory Ritter

Find the Molt Limit

A quick and dirty molt lesson that will focus on a few aspects of molt that are necessary to know if you want to understand how and why we age birds the way we do:

All birds (for our intents and purposes) undergo one main molt, or growing-in of new feathers, each year. This molt is called the prebasic molt in AHY (after hatch year) birds, and the preformative molt in HY (hatch year) birds. Molts can be complete, incomplete, or partial. During a complete molt, birds grow in all new feathers--this includes all body feathers, and all flight (wing and tail) feathers. Birds that undergo an incomplete molt will grow in new body feathers and some, but not all, flight feathers. Finally, during a partial molt, birds grow in new body feathers and a varying number of wing coverts, but generally no flight feathers.

Now, why is this important? It is important because almost every adult (AHY) bird will undergo a complete prebasic molt, but the HY birds that have a prefomative molt will usually have a partial or incomplete molt. And it is specifically this partial or incomplete molt that will allow us to see a molt limit!

Molt limits are the "boundaries between replaced and retained feathers, resulting from partial or incomplete molts" (Pyle 1997). These boundaries are visible because the newer, replaced, feathers are generally less worn and less faded than older, retained, feathers. So, if all (minus an exception or two) adult birds have complete prebasic molts, then a bird showing a molt limit must be a........................hatch year bird!

Bird Topography.

We had a typical but interesting day at Palo today, with two Varied Thrush and a brand new hatching year female Spotted Towhee.  Check out some photos and descriptions of how we age and sex these species.

HY male Varied Thrush.  Females would generally not have such dark auriculars (cheek band) and breast band. [Photo by Cory Ritter]

HY male Varied Thrush.  Most of the rectrices (tail feathers) look fairly tapered rather than truncate, which is a good sign that this bird is a HY.  HY birds of most species retain many of their juvenal flight feathers.  These feathers are grown in the nest and quickly, so the quality is much lower than those of adults. [Photo by Cory Ritter]

HY Varied Thrush.  Note the overall ratty appearance and brown wash to the head and back (brown on the back is hard to see in the photo).  The wear and overall messiness is not a definitive indicator of age, but it certainly is supportive of a first year bird.  Again, this is because juvenal flight feathers are grown rapidly, and so are of poor quality, and become worn quickly in the nest. [Photo by Cory Ritter]

Male Varied Thrush. Deeper orange and blacker black than the previous HY above. [Photo by Luke Musher]

Male Varied Thrush.  Note neater, better quality flight feathers, broad and rather truncate primary coverts, indicative of an after hatching-year bird. [Photo by Luke Musher]

These rectrices appear more tapered than those of the previous Varied Thrush.  The inner edges of the outer rectrices form a gradual curve.  After-hatch-year birds will show rectrices whose inner edges form abrupt angles.  This ambiguity kept us from aging the bird. [Photo by Luke Musher]

HY female Spotted Towhee.  Its brownish rather than blackish head, wings and back indicate that it's a female.

HY female Spotted Towhee.  This Is textbook HY rectrix shape, narrow and tapered. [Photo by Dan Lipp]

Can you find the molt limit in this photo? [Photo by Dan Lipp]

Okay okay, not the best photo, but enlarging the photo, and putting in a nice red arrow, should help you spot the molt limit. The replaced alula covert on top is darker (less faded) than the retained alula feather.  This is another clue that the towhee is a HY. [Photo by Dan Lipp]

By Cory Ritter, Luke Musher, and Dan Lipp

Socializing with Socaible Weavers

Adult sociable weaver.  Sex can't be identified in the field and we have to use genetics to identify the sex of the weavers.[Photo by Gavin Leighton]

Avian biology and behavior have contributed much to our understanding of social behaviors.  The natural world is rife with prosocial behaviors, despite the tendency for natural selection to promote selfish individuals. An especially intriguing case of cooperative behavior is displayed by Sociable Weavers (Philetairus socius).  These small birds (~30g) live in semi-arid savannah in southwestern Africa; but what sets these small passerines apart is that they live in colonies that build and maintain perennial, communal nests (See below). Interestingly, several other species of birds such as Pygmy Falcons, Rosy-faced Lovebirds, and Scaly-feathered Finches have been known to roost in the empty chambers of Sociable Weaver nests. 

Sociable weaver colony.  At the colony we trapped 108 birds. [Photo by Gavin Leighton]

The communal nest also presents an opportunity to understand the evolution of cooperative behaviors that maintain communal goods.  Theoretically, Sociable Weavers that exploit the nest-building behavior of other weavers should be selectively favored, therefore increasing selfishness.  In contrast, such selfishness is avoided, and I am interested in delimiting the evolutionary mechanisms that maintain cooperative nest construction in Sociable Weavers.

These are two rosy-faced lovebirds, one of the species of parrots in Namibia.  Common in the Khomas region, they are known to hang around sociable weaver nests and in some cases even roost in the chambers of a sociable weaver nest. [Photo by Gavin Leighton]

One possible mechanism that may maintain cooperative nest construction is kin selection.  Kin selection supports cooperative behaviors by allowing cooperative individuals to spread their genes by helping relatives reproduce, who share genes with the actor due to common ancestry.  To delineate the relatedness of Sociable Weaver colonies, I recently visited Namibia to collect blood samples from Sociable Weavers.  The weavers are trapped en masse in the morning and it often requires multiple individuals to quickly remove all the birds.  I removed blood from the trapped individuals and will be performing genetic analyses to see if the nests are composed of extended family groups. 

To complete the work, I was helped by multiple individuals from the local city.  Most of the individuals that helped with the projects were Namibian ornithologists in the region, and most of these individuals are birders by passion and have a career in a field other than avian biology.  This is probably the most salient difference between birders in the US and Namibia.  In the US, most bird banding is conducted at designated banding stations, whereas in Namibia banding is performed by a dedicated group of individuals who band on the weekends and in back yards.

Ostrich.  The red on the lower shins is indicative that this individual is in breeding condition. [Photo by Gavin Leighton]

Such banding is critical to the success of Namibian ornithology, as there are no dedicated banding stations or dedicated ornithologists at the universities.  Due to the lack of research in the country, much of the bird life in the region is still shrouded in mystery.  As an example, Ludwig’s bustard is endemic to the region, but only one individual has ever been banded, and its behavior and breeding tendencies are almost completely unknown.  The landscape is entirely wide open, and the density of birds reflects the pristine habitat; in one day we found a nest of Secretary Birds 200 meters away from a nest of Lappet-faced Vultures.  Namibia also offers diverse habitats for birds and birders; from coastal regions to two deserts, birds of all types inhabit the land of Namibia.   

Yellow Canary. [Photo by Gavin Leighton]

Purple-cheeked waxbill.  Common in the region. [Photo by Gavin Leighton]

Scaly-feathered finch.  Like Rosy-faced lovebirds, Scale-feathered finches are known to join sociable weaver feeding flocks and are also reported to roost in the chambers of sociable weaver nests. [Photo by Gavin Leighton]

 

By Gavin Leighton