Molt and Aging Birds

By Dan Lipp

Here at Palomarin, we like to keep track of how old our birds are.  Since we can’t ask a bird when it hatched, we resort to slightly more direct measures of age.  One of the best ways to determine when a bird hatched is to look to its flight feathers and wing coverts for molt limits.  You may already know that a freshly hatched bird closer resembles an amorphous blob with mold growing on it than the svelte adults we've come to know.  This is due in no small part to the hatchling’s lack of non-downy feathers.

Anna's Hummingbirds, freshly hatched.  If you squint, it looks like the inside of a 70-year-old man's ear.

During the next few weeks, while the hatchling wallows in its own filth, it will undergo its first molt, the pre-juvenal molt, and grow a complete set of feathers, termed the juvenal plumage.  These feathers actually have shafts, allowing the bird to fly.  However, they are of poorer quality than adult feathers, and tend to make the bird look like it just rolled out of bed after a 3-day meth bender.  The juvenal flight feathers tend to be narrower and more tapered than adult feathers; presumably because they need to grow at such a rapid rate to allow the nestlings to fledge in a short period of time.  Because they grow while the bird is in the nest, they  become worn and tattered rather quickly.  Juvenal feathers are often easily distinguished, by shape and wear, from the higher quality feathers that are molted later in the bird's life.

The same Anna's Hummingbirds as above 10 days later, with most of their juvenal plumage.  That'll comb right out.

The second molt that many birds go through is the pre-formative molt, which produces the formative plumage.  It isn’t until several months after the bird has fledged that it begins to molt these higher quality feathers.  However, when it replaces the flight feathers and coverts, it tends not to replace them all.  This leaves it with a somewhat predictable mix of crappy juvenal feathers and sleek adult feathers.  When this mix occurs within one feather tract (e.g. greater coverts or primaries), it is called a molt limit.  At this time of year, we can surmise that birds showing molt limits were born during the last breeding season since all adults would have gone through a complete molt--replacing off of their feathers (this only applies to birds on a complex basic strategy--see bottom for additional information on molt strategies).

Take a look at this Red-breasted Sapsucker caught in November of 2011.  Note how the brown, tattered, and tapered retained juvenal primary coverts contrast with the newer, replaced greater coverts.  Also, there is a molt limit in the secondaries (tertials AKA the three innermost secondaries have been replaced, whereas a block of worn juvenal feathers remain on the outside).  Woodpeckers are actually a little more complex with regards to age, but this example shows what a molt limit looks like.  This individual is actually a second year (pre Jan 1) or a third year (post Jan 1) bird.

He was whining a lot and acting like an immature in general.  Unfortunately, we can't use that to age them.

Another way we might come upon a molt limit is if a bird shows an eccentric replacement pattern.  Normally birds molt their flight feathers starting at P1 (primary #1) moving outwards and S1 (secondary #1) moving inwards.  However, in birds exhibiting an eccentric molt pattern, the bird will begin molting not at P1 but at a middle primary such as P3 or P4 and continue distally until its outermost wing feathers are replaced while the inner feathers are retained.

Occasionally, we see abnormalities in molt limits. We caught a Wrentit in November that essentially displayed this pattern, except that it retained its outermost primary, P10.  The difference in color is evident in the photo below.  Older feathers are a light caramel color, bleached with sun, while newer feathers are more of a darker chocolate.  Mmmm, suddenly I'm hungry.

P4 through P9 and the tertials have been replaced, while all the secondaries, 
primaries 1-3, and primary 10 were retained.

Anyway, because of the eccentric molt, we can deduce that this bird (caught in late 2011) is a hatch-year.  What's interesting is that in nearly every documented case, birds that undergo eccentric molt will complete by molting the outermost flight feather; in the case of Wrentits, that would be primary number 10.  However, if we look at the photo, we can see that P10, the outermost flight feather, is light caramel meaning that it was retained.  We asked friend of Palomarin and all-around molt wizard Steve Howell why this might be, and we were told that, likely, some environmental pressure or genetic impetus forced it to stop before it had completed its molt.  "Well, that's a data point," he said.

So what the hell do we do with this guy?  Oh yeah, I forgot; we don't catch pelicans.

Special thanks to Luke Musher and Cory Ritter for sharing their soapbox.  They run a helluva bird blog.

Additional information on molt strategies:

Since most of the birds we encounter at Palomarin are on the complex basic molt strategy, this post almost exclusively applies to birds on this system; however, keep in mind that a strong understanding of basic strategies is critical to understanding other such strategies.  The basic strategy is divided into two types, simple and complex.  The simple basic strategy means that every molt the bird goes through is the same, and thus always involves molting all feathers.  The complex basic strategy is the same except that the second molt, the pre-formative molt, is almost always partial (only molting some body feathers) to incomplete (some to all body feathers and some flight feathers), yielding different generations of feathers in the same plumage.

Get your Yellah'...bellied no good Sapsucker off my property...

Luke and I had heard about two different Yellow-bellied Sapsucker reports in Marin County during the past few months or so.  Being so far out of their range, we spent a good amount of time trying to find these birds to add to our California, and Marin County, lists. 

One was reported in Stinson Beach, CA (about 20 minutes from the field station).  We checked out this, supposedly more reliable, location a couple times without any luck.  The bird was reportedly seen in a California Peppertree next to the Sandpiper Motel, but we were unable to locate it in the Peppertree or in the surrounding neighborhood.

The other location was on Overlook Drive in Bolinas, CA (just 5 minutes down the road from Palomarin).  This spot couldn't have been any more convenient for us, as it was on the way to any destination to which we needed to drive.  We visited this spot so many times that I'm sure most of the Overlook Drive residents would recognize us in a line-up, but this Yellow-bellied Sapsucker just wouldn't turn up.

Then, a little over a week ago, French and I were making some birding stops after banding at an offsite.  It was near dark when we passed Overlook Drive on our way home, and I turned down at the last possible second.  I told French that we wouldn't even get out of the car; we'd just roll the windows down and listen.  And sure enough, I spotted some movement in a tree across the street from the address where the YBSA had been reported, and with the near-dark conditions I captured these gems.

Male Yellow-bellied Sapsucker, Overlook Drive, Bolinas, CA [photo by Cory Ritter]

Male Yellow-bellied Sapsucker, Overlook Drive, Bolinas, CA [photo by Cory Ritter]

Male Yellow-bellied Sapsucker, Overlook Drive, Bolinas, CA [photo by Cory Ritter]

Some of you may have missed the bad reference to "Home Alone" in the title here, but I found it fitting since this Yellow-bellied Sapsucker was sitting in a tree right next to a "No Trespassing" sign.

A couple of days later, Luke, Dan and I stopped back so I could show them the spot where I had seen the YBSA.  Dan had just picked up some recording equipment recently, which he had with him when we went looking.  He was unable to record any actual bird calls, but he was able to capture this other form of documentation.

On a more serious note, Yellow-bellied Sapsuckers, along with other sapsuckers, play an important role in their community.  They create and maintain sap wells in trees, from which they feed on sap.  Other species, such as the Ruby-throated Hummingbird, use these wells to supplement their diet (Walters et al. 2002).  Also, they excavate nesting cavities, which can be used by other birds (Walters et al. 2002).



By Cory Ritter


References:

Walters, E. L., E. H. Miller, and P. E. Lowther. 2002. Yellow-bellied Sapsucker (Sphyrapicus varius). In The Birds of North America, No. 662 (A. Poole and F. Gill, eds). The Birds of North America, Inc, Philadelphia, PA.

Drake's Beach Birding Photos

Dan Lipp, Cory, and I visited Drake's Beach yesterday.  Nothing too noteworthy except for two Red-necked Grebe and two Black Scoters.  Otherwise it was a pretty typical day birding Point Reyes waters.  

Marbled Godwit, Drakes Beach, Point Reyes, CA

Marbled Godwit, Drakes Beach, Point Reyes, CA

Marbled Godwit, Drakes Beach, Point Reyes, CA

Ring-billed Gull (adult), Drakes Beach, Point Reyes, CA

Mew Gull (adults), Drakes Beach, Point Reyes, CA

Marbled Godwits, Drakes Beach, Point Reyes, CA

Mew Gull (adult), Drakes Beach, Point Reyes, CA

Mew Gull, Drakes Beach, Point Reyes, CA

Western Gull (second cycle) with Mew Gulls, Drakes Beach, Point Reyes, CA

Western Gull (adult), Drakes Beach, Point Reyes, CA

Elk near Drakes Beach

By Luke Musher

More Like Boom Red-shouldered Hawka

Generally speaking, only birds up to a certain size will get caught in mist-nets meant for trapping passerines.  That size constraint is usually around the size of an American Robin, or the occasional male Sharp-shinned Hawk--as you have seen.  Birds that are any larger will usually not get tangled in the small-sized mesh of the mist-net, and are able to free themselves with a little struggle--or simply break through the net if large or strong enough.  So then, on Saturday, Dan and Cory were pleasantly surprised when they were on the closing net run and came upon this SY Red-shouldered Hawk in one of our nets. It was barely caught, so we were lucky that she didn't free herself before Dan and Cory were able to grab her. 

SY female Red-shouldered Hawk

Luke and the RSHA

Dan with the RSHA. They both look pretty confused.

Cory and the RSHA

After processing and banding the bird we did a quick search through PRBO's data and found that there have only been nine individual RSHA banded at Palomarin in the forty-six years of its existence, and only 12 captures total (i.e. some were recaptures of the same individual).  We are pretty lucky.  Even luckier was the fact that yesterday Dan and Frenchie caught another most likely second year RSHA, this time a male, at one of our offsites, Pine Gulch.  That makes two RSHA in three days (needless to say Cory and I were pretty jealous)!  To make matters more interesting, the bird has features that are quite similar to Broad-winged Hawk.  We are currently trying to confirm this bird's identity, and although we are leaning towards RSHA, it is certainly an interesting bird.  We will have more on this within the next few days.

By Cory Ritter and Luke Musher
Photos mostly by Dan Lipp

Compare-A-Sharpie

In addition to exciting birding, the new year has also ushered in a time for possible confusion. That is because birds are aged on a calendar system, so a hatch year bird on December 31st is now a second year bird on January 1st. We are comparing three different ages of Sharp-shinned Hawks (SSHA) in this post, but all three birds just passed their "birthday" and became a different age along with the new year. To reduce confusion I will try to break down how these birds are aged and how that relates to plumage differences before I get into the rest of the post.

From hatching until December 31st of that calendar year, these SSHA are considered hatch year (HY). The subsequent year they are considered second year (SY), and so on. Simple enough. But, these birds don't molt on December 31st and January 1st, so the different plumage types don't correlate exactly with their calendar age.  These birds generally molt in the fall; therefore, a SY SSHA early in the year (before molt) looks different than a SY SSHA late in the year (after molt). Also, SSHA that are past their 3rd calendar year don't show enough unique characteristics to age any farther than third year (TY) in December or after third year (ATY) in January. So, even if a SSHA is in its 5th calendar year, it would still be called an ATY.

So, to avoid confusion I will call our three Sharp-shinned Hawks juvenile, sub-adult, and adult. The juvenile hatched in 2011 and was a HY in December but a SY now, the sub-adult hatched in 2010 and just became an third year (TY) bird, and the adult hatched in 2009 or earlier and is now considered an after third year (ATY).
 
Now we will compare our two new SSHA to the one from last month in the post Birds in Hand: A Couple of Recent Favorites.

This is how we weigh birds. There is no harm done by putting the bird in a can or cup. [Photo by Luke Musher]

Here is a juvenile male Sharp-shinned Hawk. Note the yellow iris and thick, brown streaking (running the length of
 the body) as these are characteristic of juvenile SSHA. [Photo by Luke Musher]

Another look at the juvenile male Sharp-shinned Hawk. [Photo by Luke Musher]

This is the sub-adult male Sharp-shinned Hawk that we posted about last month. Note the orange iris characteristic of
 sub-adult male SSHA and the rufous barring (running across the body vs. along the length of the body) characteristic 
of older (sub-adult and adult) Sharp-shinned Hawks. [Photo by Cory Ritter]

A closer look at the sub-adult SSHA (SY last week, ASY today). Again, note the orange iris and rufous barring. [Photo
 by Cory Ritter]

This is a third male Sharp-shinned Hawk that was caught last Saturday. This SSHA is an adult based on the deep red 
iris. Therefore, this bird hatched in 2009 or earlier. So, these three Sharpies hatched in three different years. The top 
bird hatched in 2011, the middle in 2010, and this one in 2009 or earlier. Note how the rufous barring is pretty much
 the same as the middle bird, but the iris is a deeper red. [Photo by Cory Ritter]

We have caught some other pretty sweet birds lately. Below are some photos of some recent captures:

AHY Male Anna's Hummingbird. We feed hummingbirds sugar water, the same that goes into hummingbird feeders, to 
ensure they don't run low on energy during processing. This is a photo of Frenchie feeding this Anna's Hummingbird
 some sugar water. [Photo by Dan Lipp]

Here is another look at the AHY male Anna's Hummingbird. [Photo by Dan Lipp]

Cory measuring the wing-chord of a Bewick's Wren. [Photo by Dan Lipp]

Bewick's Wren posing for the camera. [Photo by Dan Lipp]

Posing, once more. [Photo by Dan Lipp]

This is Red-breasted Sapsucker was caught on New Year's Eve, and was a SY bird (now, in 2012, a third year [TY]
 bird). This photo shows the primary coverts that are uniform in wear and abraded--a trait of SY/ASY Red-breasted
 Sapsuckers. [Photo by Cory Ritter]

This photo shows more evidence of this being a SY/TY bird. There is a block of retained feathers, which are duller
 black and more worn, in the secondaries. Secondaries 1-4 are retained and 5-9 are replaced--this was the same on
 both wings.  HY/SY birds will show all secondaries of the same generation (no contrast) and ASY/ATY birds will show
a mixture of retained and replaced feathers that are neither in a block nor symmetrical on both wings. [Photo by Cory
 Ritter]

SY/TY Red-breasted Sapsucker [Photo by Cory Ritter]

So, we hope we haven't confused you by this post. There are lots of ages being thrown around in this post, and if anything doesn't make sense, please ask us and we can explain it further. Thanks!

By Cory Ritter and Luke Musher

Early (in the year) Birding and "Red" Fox Sparrow

It's early in the year, and that means there are still lots of birds to add to one's year list.  This makes for an exciting time for birding.  A time when a bird that might otherwise be common can now be exciting!  Anyways, beginning of the year aside, we heard about a really exciting bird, through the grape vine, that was seen right down the road from PRBO in Bolinas, CA.  We heard that Keith Hansen, a local artist/birder, had seen a Summer Tanager somewhere around the tennis court on Brighton Avenue in Bolinas.  We searched the area fairly well, but, much to our chagrin, we could not locate it.  We continued birding Bolinas, though.

Anna's Hummingbird, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

Starting around the tennis courts, we walked up the road leading uphill.  No Summer Tanager or eastern warblers, but lots of the common birds.  Anna's Hummingbirds were busy as ever displaying and feeding in the gardens along the road.  We then headed to the Bolinas cemetery to look for Pygmy Nuthatch (a bird both of us need for life).  We stopped to look at the wigeon flock across from the school and found two (maybe more?) female and male Eurasian Wigeon.

Eurasian Wigeon, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

At the cemetery we came across a very large flock of warblers that were, as far as we could tell, entirely Yellow-rumped (both Myrtle and Audubon's) and Townsend's Warblers.  We spent a lot of time sorting through them, but couldn't come up with anything else.

Townsend's Warbler, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

The biggest surprise of the day, though was what we believe to be a "Red" Fox Sparrow, which was feeding with a large flock of sparrows including both California and Spotted Towhees, as well as Golden-crowned, White-throated (no less than three), and Song Sparrows.  As far as we know, this race is quite rare in California, so we are hesitant to accept that it is a pure "Red."  We welcome your comments on this.

"Red" Fox Sparrow, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

"Red" Fox Sparrow, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

"Red" Fox Sparrow, Bolinas, CA. 01/03/12. [Photo by Lukas Musher]

We finished up the day birding some of the side roads off of Mesa Rd, looking again for Pygmy Nuthatch, but no luck again.  Birds around here included, Western Bluebird, White-crowned Sparrow, Townsend's Warbler, and a lone Cackling Goose in with the Canada Goose flock across Mesa Road from Overlook Drive.  On Mesa Road about one mile from PRBO we had one Say's Phoebe and a bobcat hunting in the coast guard field.

By Cory Ritter and Luke Musher