Ridges and grooves

Here's a fun set of mystery close-ups for you.

 

All of these images were taken under a microscope.  (There are some sand grains in the pictures, too.  For example, the amber-colored grains above.)

 

All of the pictures are from the same animal, just from different parts of the body.

 

Here's one more close-up, and then the next picture following this one will give the answer away, so consider yourself warned!

 

Okay, here we go.  Are you ready?  Do you have a guess?

 

All of the close-ups were the scales of a shark, probably a juvenile Salmon Shark (Lamna ditropis).  You can see some of the scales directly below the teeth in the image above.  I just found out about this shark at the end of the day, so I'm not sure I heard all of the details right...but it sounds like Matt and the Coastal Oceanography class discovered it on Salmon Creek Beach.

When I looked at the shark's skin with my hand lens I was so impressed with the scales that I couldn't resist taking a few pictures under the microscope to share with you (the shark was very small).  Note that some of the scales have very obvious longitudinal ridges.  It's thought that these ridges and grooves (running parallel to the water flow) reduce drag and thereby improve swimming performance.

This shark was in poor condition — it had probably been on the beach for a while and was partly scavenged and severely dried (next image).  But I've heard about a few other recent Salmon Shark strandings, so it's an opportunity to provide a little information about these events.

 

 [For scale, this shark was only ~2 feet long.]

For at least 20 years, juvenile Salmon Sharks have stranded on California and Oregon beaches in the late summer and early fall.  Until recently, the cause was unknown.  But last year, several researchers published a paper in which they discovered that stranded sharks had bacterial brain infections.  (It still isn't clear how or where the sharks acquire the bacteria.)

Schaffer, P.A., B. Lifland, S. Van Sommeran, D.R. Casper, and C.R. Davis. 2013. Meningoencephalitis associated with Carnobacterium maltaromaticum-like bacteria in stranded juvenile Salmon Sharks (Lamna ditropis). Veterinary Pathology 50: 412–417.

If you'd like to learn more general information about Salmon Sharks, check out the web pages provided by the Pelagic Shark Research Foundation and the Florida Museum of Natural History. 

Sunbathing

Driving home from work tonight, Eric spotted a large flock of birds perched on a few wires overhanging a field along Jonive Road.  We were late (and hungry), but turned around to get a better view.

Here's what the entire flock looked like from the road.  Because the birds are relatively small, it's probably hard to count.  If you'd like to try, remember that you can click on the picture to view a slightly larger version.  I'll reveal the actual count below the image.

 

There are 50 (exactly 50!) birds perched on the wires.  From top to bottom: 2 on the top wire, then 10, 27, and 11.

The next image will help identify the species:

 

This was a large flock of Violet-green Swallows (Tachycineta thalassina).  Here's an even closer view:

 

The Birds of North America account says that not much is known about migratory behavior in Violet-green Swallows, but mentions that there is "some flocking prior to migration."  The timing seems right for this to be a pre-migratory flock.  (Although some Violet-green Swallows overwinter in California, most will spend the winter somewhere between Mexico and Guatemala/El Salvador/Honduras.)

I wish I had an even closer view of this beautiful swallow, but there was a fence in my way.  This is the best I could do for now.

 

Many of these swallows were actively preening, but when I was reviewing the pictures, it seemed as though some of them were just basking or taking in the last rays of the setting sun (eyes closed, facing west).  

I checked the behavior section of the Birds of North America account and found this — "Reported sunbathing in large numbers on telephone wires (Bent 1942)."  I love when there's a direct match between a current observation and a description in Bent's Life Histories of North American Birds!

If I was a...

When you want to find a certain plant or animal, it's often helpful to think like them.  

This morning I was working at my desk and I looked up to see a bunting perched in the shrub outside my window.  A bunting!  I hadn't seen one on Bodega Head yet.  I didn't have binoculars or a camera nearby at the time, so I decided to try to get a closer look outside.  I saw enough to know that it was either a Lazuli or Indigo bunting, but the bird flew away almost immediately.  I looked around a bit, but couldn't relocate the bird.

At the end of the day, I decided it would be worth trying again.  I thought to myself, "Okay, if I was a bunting, where would I be?"  I generally think of buntings in weedy or shrubby habitats, so I visualized the patch of habitat like that closest to my office and headed in that direction.

When I got there, I was pretty excited to find the bunting!  This bird was extremely shy, so it took several tries to get a photograph.  I didn't end up with any high quality images, but these pictures will serve as a record.

 

The next question —is this a Lazuli Bunting or Indigo Bunting?  This is a bit of tricky one for me, as I haven't seen Indigo Buntings in years, and I have very little experience with Lazuli Buntings.

I'm leaning towards Lazuli Bunting (Passerina amoena).  The field marks that I'm using include an overall grayer plumage, distinct whitish wing bars, grayish throat, a hint of a buffy breast band, and a relatively unstreaked breast.

Although not a great photo, this one shows the throat and breast:

 

And the photo below shows the wing bars and the tail (with some bluish coloration).  Note that the feathers generally look fresh, perhaps indicating that this is a juvenile bird.

 

I'd love other opinions about the identification of this bunting — either confirming it or suggesting another species.

  

Lazuli Buntings are considered rare migrants on Bodega Head.

A new star(t)

Remember the post showing the Bat Star (Patiria miniata) larvae on 4 August 2013?  Well, those larvae continued to develop and they are now starting to metamorphose into tiny juvenile sea stars!  Here's how it happens:

The larvae develop additional arms.  At this stage, they're called brachiolaria larvae.  [In the image below, the orange structure on the right side is a juvenile rudiment.  Remarkably, it will become the juvenile sea star!]

 

Here's a better view of the the brachiolarian arms (highlighted by black arrows below).  Look for the two shorter arms reaching towards each other that are covered with adhesive papillae (tiny bumps).  The larva will use these arms to crawl around and hold on to the substrate.

 

It's hard to see in the photo above, but between the brachiolarian arms is a round adhesive disc (see below).  The brachiolarian arms now look like tiny hands on either side of the adhesive disc.

 

When it's ready to undergo metamorphosis, the larva attaches to the substrate with the adhesive disc.  It will then resorb the larval tissue and the juvenile rudiment will transform into a juvenile sea star.  

The next image shows a larva undergoing metamorphosis — the larva is attached to the bottom, most of the larval tissue is gone, the juvenile is forming but it's not fully developed yet.

 

Once the juvenile is fully developed, it will break off from the adhesive disc that's attached to the substrate and crawl away.  A newly metamorphosed juvenile Bat Star looks like this:

 

I know it's hard to tell how small this sea star is, so here's a picture with a millimeter ruler for scale (below).  Each mark represents one millimeter, so this sea star is only about 0.5 millimeters across.

 

For years we had heard about how sea stars attach to the substrate when undergoing metamorphosis from the larval to juvenile stage, but we hadn't ever seen it for ourselves.  It has been quite an experience to watch these wonderful swimming larvae develop arms with "little sticky hands" and an adhesive disc for attachment, and to see them transform into the tiniest of sea stars!

P.S.  If you're wondering, these sea stars are 47 days old (time since fertilization).

Shakedown cruise

Eric just finished teaching his summer classes, so today we went out for a "shakedown cruise" on Tomales Bay — our first sail of the summer.  We launched from Nick's Cove, sailed up towards Walker Creek, and then crossed over to White Gulch.  Below are some pictorial highlights from the afternoon:

 

Elegant Terns resting on oyster floats.

 

Harbor Seal cruising by our bow.

 

The always attractive Point Reyes shoreline.  Here's one more:

 

 

Adult Black-crowned Night-Heron perched among lichen-draped branches. 

 

Osprey, perhaps wondering if it's going to be able to finish such a large fish!

Finding frills in a boring animal

A mystery close-up for you.  Do you have a guess about what this might be?

 

Okay, here's another clue.  The next picture was taken under a microscope, but with less magnification.

 

Still need some help?  I'll zoom out a little more:

 

It might be difficult to make out, but you're looking down on the siphons of a rock-boring clam!  This is a Flat-tipped Piddock (Penitella penita).  The inhalant siphon is on the left and was the one featured in the first two photographs.  The frilly projections extending across the inhalant siphon act as a filter to keep out large unwanted debris.  The smaller exhalant siphon is on the right and has a smooth opening.  [The frill is gone.]  The entire width of the two siphons in the view above is about 15 mm across.

Flat-tipped Piddocks are probably more common than we think.  But because they're hidden in burrows in the rock, the clams themselves are generally not that visible.  The siphons are beautiful, but you'd have to be looking in a pool or under water to find and appreciate them.

This clam happened to be on the edge of a rock that collapsed, so it became exposed and it seemed like a good opportunity for a photograph of this seldom-seen animal.  

The clam has a somewhat unusual shape (see below), with a very bulbous rounded end that sits at the bottom of the burrow and an elongated leathery portion that reaches to the surface of the burrow.  Look for the many rough lines of "teeth" on the outer surface of the shell.  The clam uses these teeth to rasp away at the rock.  It rocks back and forth, moves up and down, and rotates around and around, to create a long, smooth, circular burrow.  (You may occasionally discover these burrows in rocks washed up on local beaches!)

 

To the roost

Tonight I was thinking about a friend who used to sit out in his yard at the end of the day and watch the sky for activity — birds flying by, butterflies coming into roost.  I decided to give it a try.

It was a beautiful night.  The clouds were amazing and there was quite a bit of bird activity.  Not long after I sat down, I was a little shocked to see a Peregrine Falcon fly by.  This is my 9th year in this house, and that's the first Peregrine Falcon I've seen here.  Perhaps I should be sitting down to look up at the sky more often!

At about 7:20 p.m. I started to notice flocks of American Crows (Corvus brachyrhynchos). Sometimes it would just be a few birds, but other times over 20 birds flew by at once.  Here's the first group I photographed.  How many crows do you count in the image below?

 

(I counted 10 individuals.)

Flocks of crows continued to appear in pulses.  Occasionally they'd call, but mostly they'd fly by silently.  How many crows do you count in the next image?

 

(I counted 18 individuals.)

I kept watching.  And I kept counting.  At about 7:50 p.m. the background noise, i.e., all of the anthropogenic sounds, got noticeably quieter.  This made it interesting as I could then hear the wings of the crows as they approached and flew overhead.  How many crows do you see in the image below?

 

(I counted 9 individuals.)

I wrapped up around 8 p.m.  Although I didn't do a great job counting because I was also trying to take photographs, I counted at least 150 crows in about 40 minutes.  All of the crows were flying from the southeast to the northwest.  It appears that there is a communal roost somewhere in that direction!

Crow roosts may consist of hundreds to thousands (or even millions) of individuals.  The number of individuals in a roost increases after the breeding season and peaks in early to mid-winter.  Roost behavior has been studied in several locations.  In one study they found that most crows begin to arrive at the roost site about 30-40 minutes before sunset.  And in another they found that the majority of individuals have entered the roost site in the window that spans 10 minutes before and 10 minutes after sunset.

A few birds stopped briefly before continuing on.  I wonder where their roost site is?

 

I'm very thankful for a summer evening with shape-shifting clouds and surreptitious crows!