For a long time now I've wanted to document a phenomenon that I've observed many times: the way that some birds change color when they move from the light into the dark. I'm sure you've noticed this before, in the vibrance of a peacock's tail that turns to black when the bird moves into the shade. But have you ever thought about why some feathers change color with changing light, while others don't?
It turns out that there is more than one explanation for feather color. Some feathers are colored because of the pigments they contain. Pigments are molecules that absorb some wavelengths of light and reflect others; the wavelengths that are reflected are detected by our eyes and interpreted by our brain as color. There are three groups of pigments that occur in feathers, each of which contributes certain colors to a bird's plumage: (1) melanins--responsible for pale yellows, dark browns, and blacks; (2) porphyrins--producing reds, pinks, browns, and greens; (3) carotenoids--contributing bright yellows and oranges. Pigments can work in concert, too, as when melanins and carotenoids combine to produce olive-green.
Pigment molecules are independent from the underlying structure of a feather. It turns out that the structure itself can produce color. For example, the blue in the feathers of Steller's jays (Cyanocitta stelleri) is due to scattering of light by tiny air pockets in the feathers. When sunlight strikes the filament of a feather, the blue wavelengths are refracted back into the atmosphere where they can be picked up by our retinas, and the other wavelengths are absorbed by a layer of melanin at the base of the filament (which is why we don't see them).
A second kind of structural color is iridescence. This is due to the microscopic structure of the feather's barbules. These barbules act like prisms, refracting light as it hits the feather. The appearance of the light (brighter or darker) changes as the angle of viewing changes.
My favorite example of iridescence in birds is in the hummingbirds. These ornithological gems flit about so rapidly that it can be hard to get a good look at them, but their brilliant colors are stunning. This afternoon I was finally able to take a series of photographs that show how minute changes in a hummer's posture can change its coloration. This male Anna's hummingbird (Calypte anna) posed very nicely and allowed me to snap off a series of photos. In this series of photos I have edited them only to crop them to the same size and center the bird in each one. I have made no adjustments to color or saturation.
And to drive home just how brilliant that pink head is, here's a shot of the same bird, this time on the opposite side of the feeder.
Anybody who says pink isn't a masculine color has obviously never seen a male Anna's hummingbird in full sun!
This week I took my Ecology students to the Younger Lagoon Reserve (YLR) on the UC Santa Cruz Coastal Science Campus. The YLR is one of 39 natural reserves in all of the major ecosystems throughout the state of California. The UCSC campus administers five of the reserves: Younger Lagoon, the Campus Reserve, Fort Ord Natural Reserve, Año Nuevo (operated in conjunction with the California State Park system), and the Big Creek Natural Reserve in Big Sur. The UC reserves are lands that have been set aside to use as living laboratories and outdoor classrooms, and are fantastic places to take students to learn about the natural history of California. They provide students with opportunities to gain valuable hands-on experience working in the field, through classes, internships, or volunteering.
The Younger Lagoon Reserve comprises about 70 acres of land, most of which was formerly brussels sprouts fields. The lagoon itself is a Y-shaped body of brackish water that receives input from run-off due to rain. It connects with the water of Monterey Bay only when there is enough freshwater flowing to break through the thick sand berm; this happens once or twice a year during the rainy season. The Lagoon lands were donated to UCSC in the 1970s. East of the actual lagoon are about 47 acres of what are referred to as Terrace Lands, which were incorporated into the YLR in 2009. This is where, for the past three years, I've brought students to work on vegetation restoration. The team of reserve stewards, interns, and volunteers has a yearly goal to replant two acres every year.
This year, instead of getting straight to the planting, we began the morning at the bird banding station. Personnel at the YLR have been banding birds for a little over a year now, usually on Fridays and occasionally on Thursdays. The banders, or "bird nerds", get started at about 07:30, and by the time our class arrived at 09:30 they had caught five birds. It was windy and there was no cloud cover at all, which were not very good conditions for catching birds in either the mist nets or the ground traps.
Notice how both the mist net and the ground trap are empty? That's the kind of luck we had with the bird banding.
The rest of the morning was very productive. After the bird banding demonstration we joined the UCSC student interns on the Terrace Lands for some planting. The method used for planting has changed since the last time I was here with students in 2016, due to a 5-year study comparing weed control methods. Herbicide was very effective, but obviously toxic to the native plants as well as the weeds. The stewards also tried laying black plastic over the fields and letting the sun bake the weeds to death. This was almost as effective as herbicide; however, the plastic can be used only a few times and then has to be thrown away to end up in the landfill. The result of the study was a compromise between effective weed control and minimal negative environmental impact. The planters now put down a layer of biodegradable paper and cover it with mulch. Holes are punched through the paper and small plants are planted in the holes. The combination of the paper and mulch seems to work pretty well. Plus, there's no waste!
A large group of about 25 motivated workers can accomplish quite a lot in a few hours. By lunchtime we had lain three long strips of the paper side-by-side, covered them with mulch, and repeated the process twice more, using up the entire roll of paper. The hole-punching and planting go more slowly, but we did place ~200 plants in the ground. It was a busy and productive morning, despite the lack of birds. The students said they learned a lot and had fun doing it. That's the beauty of field trips!
Here's another photo, taken from farther away to give you a bigger picture of the scale of things.
Believe it or not, the maker of these trails is the little black turban snail, Tegula funebralis. They are one of my favorite animals in the intertidal, for a number of reasons:
I always root for the underdog and the under-appreciated, and these snails are so numerous in the intertidal that they are practically invisible. People literally do not see them. I know, because I ask.
They are very useful creatures to keep as lab pets. I throw a few of them into each of my seawater tables, except for the table that contains a resident free-ranging sea star, and they do a fantastic job keeping algal growth to a tolerable minimum. They're my little marine lawnmowers!
They come in very handy when I'm teaching invertebrate zoology. Students study them live to observe behavior, and the snails are not shy. They are very tolerant of being picked up and gently prodded, and soon emerge from their shells and carry on their little snail lives. Students also dissect them in lab to learn about gastropod anatomy.
So yes, these tracks in the sand are made by T. funebralis in the high intertidal. In areas where a layer of sand accumulates either at the bottom of a pool or on a flat exposed rock, it is not uncommon to see a turban snail pushing sand out of the way as it crawls along, like a miniature snow plow.
Tegula funebralis and its congeners are called turban snails because their shells are shaped like turbans. Given their small size (a big T. funebralis would have a shell height of 2.5-3 cm), pushing sand around must be a tiresome chore. They do it because they have no choice. Most grazing gastropods, such as turban snails and limpets, can feed only when they are crawling. There may very well be a nice yummy layer of algal scum on the surface of this rock, but the snail has to push the sand out of the way before it can feed on it.
Here's another photo, taken at the snail's level.
This snail is pushing through a wall of sand as tall as itself! I don't know about you, but I sure as heck couldn't do that. Props to these little snails!
This week's field trip for my Ecology class was the first of two visits to the Santa Cruz harbor. The students' task was to select a site to monitor for a semester-long study of ecological succession. The floating docks at the harbor are the ideal site for this kind of study because I know from experience that the biota changes from season to season throughout the year, on a time scale that can be observed within the confines of a 16-week semester. We will return to the harbor in nine weeks and students will document how their sites have changed in that time.
California is swinging back into the severe drought situation we had before the epic 2016-2017 rainy season. Since the current rainy season began on 1 October 2017, we've had hardly any rain at all and very little snow in the Sierra. Fools who thought that one rainy season would get us out of drought are just that--fools. However, one nice thing about drought conditions is that visibility at the harbor is pretty good. Without any significant runoff the water is nice and clear, making it easy for the students to see what's growing on their section of the docks.
The assignment for this first visit to the harbor was to choose a site, identify what lives on the site, and draw a map of it. I had warned them that all the interesting biology on the docks occurs below the level of their feet, and that they would have to lie or kneel on the dock to get a good look at what's going on down there. Some of them tried to take a photo of the entire site, but it's impossible to get far enough away. Unless you're actually in the water, from where it would be easy. Yeah, you could don a wetsuit and get in the water, but the harbor isn't the most ideal place to go for a morning swim.
A little back story on the docks at the Santa Cruz harbor
Remember the magnitude 9.0 earthquake and subsequent tsunami that occurred in northern Japan several years ago? That was on 11 March 2011 at 14:46 local time. That morning in Santa Cruz we received a tsunami warning. I didn't venture down to the harbor (I think I was working at the marine lab that day) but here's a video shot by a woman who watched the ~0.5 meter tsunami tear through the upper harbor:
Amazing, the destructive power of such a small wave, isn't it? Boats were wrenched from their moorings and slammed into other boats and harbor infrastructure. I forget the total dollar amount of damage that our harbor sustained, but as a result all of the docks were replaced in the next few years. I did happen to be at the harbor with a group of students on one of the days that the old docks were being removed. It was heartbreaking to see the docks, carrying decades of biological growth on them, dumped in the parking lot to dry out in the afternoon sun. I imagine they were eventually hauled out to the landfill.
Since then, the biota on the new floating docks seems finally to be stabilizing. If I had been teaching Ecology back in 2013, we would have had pristine habitat in which to observe honest-to-goodness primary succession. As things are, however, I'm giving students the option of scraping all or part of their plot clear, to simulate primary succession. Their other option is to leave the plot as-is, and pick up the succession process somewhere in the middle and see what happens from this point forward.
So, what did they see down there?
Well, even though the water was relatively clear, a lot of the photos looked like this:
I can identify much of the stuff in this photo, but this isn't the best shot to showcase the biodiversity on the docks. I decided that the camera would do a better job if I used it to photograph individual organisms instead. Here are some of my favorites.
This shot is looking straight down along the edge of one of the docks. The macroscopic life begins 2-3 cm below the waterline, and even above that the dock surface is covered with microscopic scuzzes.
I had shown the students pictures of organisms they would be likely to see at the harbor. One of the critters that shows up sporadically is the introduced hydroid Ectopleura crocea. Later in the semester we will discuss species introductions and invasions in more detail. Harbors generally tend to be heavily populated by non-native species, and our local harbor is no exception. The species of Ectopleura found in harbors has hydranths that can be 8-10 cm long, and when it occurs it tends to be quite conspicuous. The congeneric species, E. marina, lives in intertidal in some areas on the open coast; I've seen it in a few tidepools at Davenport Landing, for example. The intertidal species is much smaller, about 2-3 cm tall and doesn't form the dense clumps that typifies E. crocea.
The ubiquitous caprellid amphipods were crawling all over everything, as usual. Some of the students really didn't like these guys and one of them had the same reaction to them that I do, which is a general shudder. They're sort of cute in still photos, but when they start inchworming around they look sort of creepy. And when there's a bunch of them writhing around in an oozy mass, they're REALLY creepy.
One of the most conspicuous worms at the harbor is Eudistylia polymorphora, the so-called feather duster worm. They come in oranges, purples, and yellows. This one was pure white. Lovely animal!
Tube-dwelling polychaete worms, such as Eudistylia, don't have much in the way of a head but they do have many light-sensitive eyespots on the tentacles. They react very quickly to many stimuli, and even a shadow passing over a worm causes it to yank its tentacles into its tube in the blink of an eye. Usually they're not too shy, though, and will extend their tentacles soon to resume feeding.
All told we were on the docks for about 2.5 hours. Not a bad way to spend a glorious morning, is it?