We Californians are all under a state-wide mandate to stay at home, to minimize the spread of COVID-19 this spring. School hasn't been cancelled, but all classes have converted to distance learning. I had four days to figure out how to deal with that. Fortunately we are in spring break this week, which gives us all a little bit of a breather. I'm going to use the time to catch up on grading and plan for the second half of the semester.
The marine lab is also closed for business. Only essential personnel are allowed to be there. The term 'essential personnel' includes people whose responsibilities are animal husbandry. Since animals will die if I'm not there to feed them, I have met that criterion for essentiality. That's not a word, but you know what I mean. With so many fewer than usual people at the marine lab, there's a lot more wildlife activity. A few days ago I saw a long-tailed weasel (Mustela frenata) chase down and capture a young brush rabbit. I just barely had time to catch a quick shot with my phone.
The most noticeable thing, though, is the increased birdsong. The sparrows, finches, red-winged blackbirds, mallards, doves, towhees, and hawks are all making a lot of noise. The barn swallows (Hirundo rustica) returned to the lab on the 21st, right on time! Maybe this year they'll have a more successful nesting season than they did last year.
Yesterday I witnessed something I'd never seen before: a territorial dispute between a black phoebe (Sayornis nigricans) and a barn swallow. The fact that I had never seen it before in no way implies that it happens only rarely; maybe I've just never paid that much attention to these things before, or they've never happened while I've been around to watch.
Here's the story, in a series of snapshots.
Prologue. The barn swallow (H. rustica) is perched on one of the outdoor light fixtures. The phoebe (S. nigricans) swoops up from below.
The swallow takes to the air, only to be divebombed by the phoebe.
The swallow retreats. . .
. . . and the phoebe perches, triumphant, on the rain gutter.
The entire altercation lasted maybe as long as four seconds. I didn't see where the swallow flew. The phoebe remained on the rain gutter for about a minute or so, then took off over the meadow. Perhaps it has a nest somewhere nearby and was defending it. Both species build mud nests on cliffs and buildings, so these birds could be competing for nest sites. Or maybe phoebes just don't like swallows. Either way, this was the sort of interaction that I don't notice when there is a lot more human activity at the marine lab. Nature has a way of re-asserting herself when humans are removed from the scene for even a short period of time.
It's no secret that I love pelicans. I love watching them soar low over the waves, where they are truly in their element. I love watching them plunge from the air into the water and then bob right back to the surface, because unlike their cormorant relatives, pelicans can't fly underwater. And I love watching them plunk around on land, where they are dumpy and awkward but still somehow elegant.
The other day I ventured out between storms to photograph birds. As per usual I ended up down at Natural Bridges, where pelicans were hanging out on the last remaining rock arch. They were well within the reach of my long lens, so I took a lot of photos.
The best photos I got were of a subadult pelican coming in for a landing.
Landing gear down!
Decreasing air speed:
And. . . touchdown!
A job well done!
The youngster managed a safe landing without knocking one of its compadres into the water. That isn't always the case--those wings can do a lot of damage. But the three adult birds on the left hardly seemed to notice, which means the youngster has learned how to stick the landing without disturbing everyone else in the vicinity. I'm sure that's a lot easier said than done!
Autumn is migration season in California. We all know that, in the northern hemisphere, birds fly south for the winter and return north for the summer. And indeed, this is a very good time to go bird watching along the Pacific Flyway, as migrating birds stop to rest and feed at places such as Elkhorn Slough. Here in Santa Cruz, autumn is punctuated by the return of monarch butterflies (Danaus plexippus), roosting in eucalyptus trees at Natural Bridges State Beach and Lighthouse Field.
Since 1997 the Xerces Society for Invertebrate Conservation has been tracking monarch sightings on their migrations between the western U.S. and Mexico. They conduct a volunteer butterfly count every Thanksgiving. More recently, community science data sources such as iNaturalist provide much of the information.
This morning, before it got warm, I went to Natural Bridges to see how the monarchs were doing. I wanted to photograph clumps of butterflies dripping from tree branches. It seemed, however, that there aren't as many butterflies as I remember from previous years. The clusters were not nearly as large or as dense as they should be. And the data shown in the figure below do demonstrate a precipitous decline in monarch since 2017. We're still a couple of weeks away from this year's Thanksgiving count, and there is still a chance that the butterflies might arrive in larger numbers.
Trained observers know how to estimate the number of butterflies in a cluster like this. The numbers of butterflies at various roosting sites are aggregated to assess overall population sizes.
This morning I did see one butterfly that had a tagged wing. It was wearing a green Avery round sticker, with some writing in what looks like black Sharpie. The color of the sticker was very close to the green of the surrounding foliage, so I wasn't even able to see the sticker until I downloaded the pictures from the camera.
At first I thought the tag resulted from an official scientific project or undertaking, but it turns out that anyone can tag a monarch. The tags are used to track migration of the butterflies. There doesn't seem to be a central depository of tags and their origins, so knowing the color of the tag doesn't tell me where this particular butterfly came from.
Once the sun hits the butterflies and they begin to warm up, the clusters start breaking apart. Butterflies open and close their wings, exposing the darker dorsal surfaces to the sun and warming up their flight muscles. Sometimes they dislodge one another.
On a cool morning like this, many of the butterflies that fell out of the clump couldn't fly yet, and landed on the ground. The boardwalk is perhaps not the safest place for a butterfly to wind up, but at least in a monarch sanctuary such as Natural Bridges the visitors are knowledgeable and look out for the butterflies' safety.
As I wrote before, the butterflies we see at Natural Bridges this year were not born here. This means that their survival to this point has depended on healthy conditions in the Pacific Northwest and the western slopes of the Rocky Mountains, where they lived as caterpillars and emerged from their chrysalises. This also means that planting milkweed for monarch caterpillars in California won't help the butterflies that we see here, although it would help butterflies that are destined to overwinter elsewhere. What will help local butterflies--monarchs and otherwise, and all nectar-feeding insects, in fact--is planting California native plants, to provide them with the nutrition they have evolved to survive on.
People call them air rats or trash birds, but I really like gulls. Especially the western gull (Larus occidentalis), known colloquially among birders as the WEGU. Yes, gulls eat garbage, but that's only because humans are so good at making garbage and leaving it all over the place. Other gulls may travel quite far inland--in fact, the state bird of Utah is the California gull (Larus californicus)--but the WEGU is a California Current endemic species. This means that its natural food sources are the fishes and invertebrates of the California Current, which flows southwards along the west coast of North America. As a result, it lives in only a very narrow strip of coastline, nesting on cliffs and restaurant roofs.
Case in point. Yesterday afternoon I was at Moss Landing with my marine biology students. We had hiked along the road, over the dune to the beach, down the beach a ways, and returned over the dune to circle back to our starting point. The last item of note that we all watched was a western gull hunting along the shoreline of the Moss Landing harbor.
It had grabbed a crab. It looked like a rock crab, but I couldn't tell what species.
The crab wasn't dead, and was thrashing around enough to make it difficult for the gull to get a good grip on it.
The crab gets a reprieve!
But the gull didn't give up. It reached down, came back with the crab in its beak, and then flew off.
Over the holiday weekend I was in Morro Bay for a surprise 80th birthday party--not mine! The party on Friday evening was a huge success (none of the guests let the cat out of the bag), the birthday girl was completely taken by surprise, and a good time was had by all. The weather was cold and sporadically stormy the entire weekend, but the clear spells between storm squalls were gorgeous and almost a little warm.
Since it wasn't raining on Saturday morning, we went out to Morro Rock to look for peregrine falcons. There are two (I think) pairs of falcons nesting on the Rock, one of which nests on the side of the rock that is visible to people. This is nesting season, and Morro Rock has a lot of ledges that make good nesting platforms. Peregrines don't make a nest, really. They lay eggs and incubate them on ledge high up on structures--rock cliffs, buildings, bridges--that dominate the landscape. We did see one peregrine way up on the rock, identifiable through binoculars but far enough away that I couldn't get a decent photo. This is the best I could do:
So not much success with the falcons, although I could at least document that they were there. Turning away from the Rock I was able to watch a great blue heron (Ardea herodias) go after and catch and eat a juvenile rockfish! The photos tell the story, so I'll just post them.
And finally, down the hatch it goes:
And there you have it! On a day when it was too blustery for human fishers to venture out of the bay, one avian predator had a successful morning. Way to go, bird!
People who moved here from other states often say that California doesn't really have seasons. I think what they mean is that in general we don't oscillate between frigid winters and hot, humid summers. The Pacific Ocean moderates weather conditions through most of the state, giving us our Mediterranean climate characterized by a short rainy season and a long dry summer. However, California is a very large state with many different climate zones. Here on the coast our summers are cool and foggy, while in the interior of the state summers can be quite hot, upwards of 38° C for weeks at a time. Snow falls in the Sierra Nevada, providing much of the state's annual water budget, but the rest of the state usually remains snow-free for most of the winter.
That said, California does of course have seasons, even though they may not be as in-your-face as what you'd see in, say, New England. One of the ways to experience the seasons is to observe the comings and goings of migratory wildlife, especially birds. In fact, bird migration patterns make up a significant part of phenology, the study of the timing of biological events in the natural world. California's position along the Pacific Flyway provides fantastic bird watching opportunities throughout the year. There are many locations within California that are pit stops for birds migrating up and down the coast and overwintering oases for birds that breed much farther north.
The San Luis National Wildlife Refuge (NWR) in Merced County is one such place. Located in the Central Valley, it represents some of the original habitat in this part of the state. The San Joaquin River winds through the Reserve, providing riparian habitat, although the river is currently a mere ghost of its former glory. Since 2009, federal and state entities have worked to restore the San Joaquin, increasing water flows and cleaning up the surrounding lands. While it would be marvelous to see chinook salmon once again migrating from San Francisco Bay up the San Joaquin, it hasn't happened yet. The re-establishment of salmon runs up to just below Friant Dam would indicate a healthy San Joaquin River, and I really hope to see it in my lifetime.
Before the era of modern agriculture, much of the Central Valley flooded with the winter rains and spring snowmelt. Only a tiny fraction of these wetlands remain; most have been drained for agriculture and further deprived of water by state and federal water diversion projects. In areas such as these, small pools form during the wet season. These vernal pools--so called because they are often at their deepest during the spring--are ephemeral habitats. They almost always disappear during the long dry summer, but during their short existence they provide living space for a unique biota. A few vernal pools occur in most of the flat areas of California, although there are far fewer of them than before, and they differ biologically throughout the state. It is not uncommon for each vernal pool in a given area to have its own combination of flora and fauna, all of which have adapted to thrive in both desiccated and flooded conditions.
On our way back to the coast after spending Christmas with my family, we stopped at the San Luis NWR to do some wildlife watching. The visitor center was closed because of the federal government shutdown, but the roads were open. The Refuge has two auto tour routes, one to the tule elk reserve and the other to see resident and visiting aquatic birds. We chose to drive the bird route, because winter is a good time to see birds that spend the rest of the year at much higher latitudes.
Coots (Fulica americana) are ubiquitous in California's wetland habitats, and because of that they are easily overlooked. When I was little we called them 'mudhens' and smirked at them because they weren't ducks. Of course I now realize that that thinking is entirely unfair, and have come to appreciate coots because they aren't ducks.
In addition to the coots, which weren't much of a surprise because we expected to see them, we saw large numbers of several species that we weren't as familiar with. There were ducks and geese, which took us some time to ID because they weren't mallards and Canada geese. Fortunately I keep a bird field guide and binoculars in the car! My favorite bird ID book is the National Geographic Field Guide to the Birds of North America; we keep one of the later editions at home, but my beloved and well battered third edition lives in the glove compartment.
The ducks turned out to be northern shovelers, which I've seen at Elkhorn Slough. True to the typical avian way of doing things, the males are strikingly colored, with brilliant green heads, while the females are a dark streaky brown. In the photo below, a female swims with two males.
The geese were entirely new to us. We first saw them flying overhead in the V-shaped formations that you expect from a gaggle of geese in the air. But they didn't honk like Canada geese so we knew right away that they were something different.
I wasn't able to ID these until we got home and I looked at my photos on the computer. iNaturalist helpfully gave me a tentative ID of greater white-fronted goose (Anser albifrons), which I was happy to go along with.
In North America, greater white-fronted geese nest in the Arctic of western Canada and through most of Alaska, including out along the Aleutians. They migrate south to spend the winter along the Gulf coast and along the eastern coast of the Sea of Cortez. The winter wetlands of the Sacramento and San Joaquin Valleys host many of these geese, and smaller numbers overwinter in coastal Oregon and Washington.
Living in California, I don't usually expect to encounter any species whose common name includes the word 'tundra', but tundra swans do indeed spend their winters here! They nest in the very high Arctic on tundra, a habitat that is threatened by climate change, and winter is the only time we would see them in the lower 48, when large flocks venture south to overwinter near lakes and estuaries. I'll keep an eye out for them next time I'm at Elkhorn Slough or Moss Landing.
We saw hundreds of these swans hanging out with the shovelers. Only a few were within photograph range, as I don't have a very long telephoto lens (yet!), but there were lots of large white blobs floating, foraging, preening, and sleeping. They were fun to watch through the binoculars. We had hoped to see some sandhill cranes in the Refuge, too. We had seen them off in the distance, much too far to be photographed, but it wasn't until we were on the last leg of the auto tour that we saw them up close. They were not mingling with the swans and geese, and as far as we could tell tended to gather in single-species flocks. They seemed to be more skittish, too, and would startle and fly away when they heard human noises. I had to move slowly and quietly to get this close to them. Even the sound of the camera shutter caught their attention and made them wary.
The Central Valley is Ground Zero for sandhill cranes in California, where they can be seen only in the winter. They don't breed here, of course, but there is a small population of ~460 pairs of sandhill cranes breeding in far northeastern California. There are locations in the Central Valley that are known for hosting large crane populations in the winter, and one of my goals is to witness a big 'fly-in' event, when huge flocks come in to roost in the evening. I've seen pictures, and it looks like a spectacular sight. I want to see it with my own eyes.
All this is to say that we do indeed have seasons in California. The shifts between summer and winter are perhaps more subtle here than in other states, but an observant eye keeps track of changes in the natural world. And you don't have to be a trained scientist to track seasonal changes wherever you live, either. We tend to use temperature to tell us which season we're in, but in reality light is a much more reliable indicator. Just think of how dramatically temperature can fluctuate in a few days, and how much more extreme these fluctuations seem to be in recent years, due to climate change. Day length cycles, however, remain constant over geologic time, as we humans haven't yet figured out a way to mess with the tilt of the earth's axis. Everyone notices how the amount and quality of light change with the seasons. It takes just a little more effort to notice the ways that life responds to those changes.
A few years ago I had a student, Brett, who had played baseball while he was in high school. One day in lab the students and I were chatting about nothing in particular when the conversation turned to the difficulty of memorizing the scientific names of all the animals they were studying. We got into one of those debates about the usefulness of common names as opposed to scientific names, and I got on my soapbox to deliver my usual sermon: common names are fine, if you are talking with non-scientists and as long as the names are unambiguous, but for scientific communication and to avoid confusion and ambiguity you need to use an organism's scientific name. Also, taxa that have been well studied for decades or centuries, such as birds and flowers, often have common names that are widely accepted and used by both scientists and naturalists. This evolved into a discussion of bird-watching and how birders have developed a sort of shorthand for birds' common names; RTHA for red-tailed hawk (Buteo jamaicensis), for example.
At this point Brett chimed in with a bit of wisdom imparted by one of his high school baseball coaches, who said, "All you need to know to identify birds is whether or not it has webbed feet. If it has webbed feet, it's a duck! And if it doesn't have webbed feet, it's a pigeon!" I must say, as far as methods for distinguishing different groups of birds, I have heard worse. The possession of webbed feet at least has a functional significance, and it's usually easy enough to see a bird's feet, or at least to infer the presence or absence of webbing by observing the bird in its habitat.
My own proficiency at IDing birds is sketchy at best. I'm pretty good with the birds that I see all the time in my backyard and canyon, and I can get most other sightings down to major group, but there are some types that I will probably always find difficult. Gulls and the wading shorebirds, for example. Gulls are notoriously problematic because there are many species and they go through three or four juvenile stages before attaining adult plumage. Wading shorebirds (sanderlings, and whatnot) all look alike to me, and absolute size differences are hard to discern when dozens or hundreds of birds running up and down the beach are about the same size.
One bird that I can easily identify based on its silhouette, is a cormorant. They are related to pelicans and have the same gular pouch under the throat that they use to catch fish, but are their bodies are much more streamlined. Unlike pelicans, which dive from the air to catch fish, cormorants are pursuit divers, using their webbed feet to swim after fish below the surface. These webbed feet are located at the posterior end of the body, where they are well positioned for propulsion under water (think about where a submarine's propeller is located). Having their feet at the back end of the body gives cormorants a more upright stance on land compared to pelicans, whose feet are positioned towards the middle of the body and thus carry themselves along a more horizontal axis.
Clearly, despite their webbed feet, cormorants are not ducks. However, like ducks they do spend most of their time on or in the water. Cormorants are unusual for aquatic birds in that they don't have oil in their feathers. You've heard the phrase "Like water off a duck's back", right? It means not being affected by external events, instead letting them roll off and away the way that water beads and falls off a duck's plumage. The saying is true because ducks and other waterfowl do indeed have a coat of oil in their feathers. In fact, most birds have feathers that are water-repellent to some degree. The oil keeps water from penetrating through the feathers and chilling the body. It also provides additional buoyancy. When you see a bird preening, part of what it is doing is distributing the oils over the feathers in an even coat.
Not having oiled feathers, cormorants soon become waterlogged, which enables them to stay underwater and swim efficiently below the surface. Unfortunately, getting soaked to the skin means the cormorants are susceptible to hypothermia. When they have finished feeding, they need prepare their feathers before they can make any prolonged flights. You will often see cormorants perched on rocks or cliff ledges, basking with their backs to the sun and wings outstretched. They have to do this to dry their wings and warm up their bodies before they can fly. Their dark coloration absorbs heat quickly and speeds up the drying process.
Even though they don't have oiled feathers, cormorants do spend a lot of time preening. They use their beak to smooth feathers and make sure they lie properly on the body. Usually they pay special attention to the wing feathers, as the proper condition and alignment of these feathers makes flight possible.
Another characteristic that makes cormorants different from ducks is their solid bones. Almost all of the flying birds have hollow bones, to lighten the load they have to carry through the air. Flight is a very energetically expensive endeavor, and over millennia the hollow skeleton has evolved to make it slightly less so. Penguins, of course, do not fly in air, but their swimming motion is essentially underwater flight. They have solid bones, to provide weight and counteract the positive buoyancy generated by their blubber and oiled feathers. Like their flightless tuxedo-wearing relatives, cormorants also have solid bones, to help keep them underwater as they pursue fish.
The hitch in this plan for cormorants, however, is that they do fly. Cormorants travel through the air and hunt for prey in cold water. They certainly aren't the only birds with this combination of habits; there are tern species, for example, that migrate thousands of miles and feed by plunge diving. But cormorants, being pursuit divers, spend more time underwater than most other flying birds. They have had to evolve a combination of adaptations for flight (flight feathers, wings long enough to enable flying) and adaptations for swimming underwater (legs at the back of the body, lack of oil in feathers, and dense bones). Natural selection is often about just this sort of compromise. An organism doesn't have to be perfect to be fit for its environment, but it does have to be good enough. And when an animal spends time in both air and water, it has to be good enough in two environments. Cormorants, traveling through air and hunting in water, manage to be successful at both and thus persist.
About a week ago, as part of yearly summer fire prevention, some of the fields at the marine lab were mown. After this happens many of the little critters living in the dried grasses are left homeless and become relatively easy prey for predators of all sorts. Since the mowing I had been seeing a great blue heron hunting in the field, and it took me until the day before yesterday to remember to bring the camera with me. Fortunately it was overcast that morning and the heron was there!
I watched the heron hunt (unsuccessfully) for a while, then my attention was drawn to a much more dynamic avian predator. A juvenile red-tailed hawk, possibly the one that grew up and fledged from the nest across the canyon from my house, flew overhead and perched in a cypress tree. From there it had a birds-eye view of the field, and it didn't take long for it to spot a late breakfast. The heron left, squawking loudly to protest the interruption to its hunting.
The hawk actually skinned the rodent before eating it. . .
. . . and then it ate the skin!
The hawk did not linger on the ground after eating its rodent prey. It flew back across the road up to the cypress tree again. I got lucky and managed to catch a few shots as it flew by.
Of course, I have no way of knowing if this young hawk is indeed the one we watched grow up. I'm reasonably certain that the marine lab is in the parents' foraging territory, as I've watched them leave the nest site and fly towards the lab. At some point the juvenile will have to disperse away from its parents and establish a territory elsewhere. In the meantime, it, along with other birds of prey, will have easy pickings in the fields. This has been a banner year for wood rats and gophers (ugh!), which means there should be plenty of food to go around.
By the way, the heron did not catch any rodents while I was watching. It did not return after the hawk arrived.
This morning, after months of invitations that I could not accept due to teaching commitments, I was finally able to join a group of folks at the Younger Lagoon Reserve (YLR) for their weekly bird banding activities. During the summer months they start early, trying to catch birds in the few hours after dawn. I didn't get out there until almost 07:00, and they had been "fishing" for about 45 minutes already. They were finishing up the process with a Wilson's warbler and went out to release the bird as I came up.
Bird banding activities are overseen by a person who holds state and federal permits to work with birds. The permit holder for the Younger Lagoon Reserve and the Fort Ord Natural Reserve is Breck Tyler. Either he or his partner, Martha, must be on site whenever birds are being banded. The other regular participants are YLR staff members Vaughan Williams (Restoration Field Manager), Kyla Roessler (Assistant Restoration Steward), and various UCSC undergrads who are interns, volunteers, or students visiting with classes. Back in March I brought my Ecology students to YLR to observe bird banding and work on vegetation restoration in the Reserve's terrace lands; on that day we did help with planting, but got skunked on birds.
When I arrived this morning it was sunny and cool. Vaughan told me that the best weather for bird banding is one of the overcast, foggy mornings that we often get in the summer. When it's sunny, like it was today, the birds can see and avoid the nets.
The mist nets are made of an extremely fine nylon mesh. They are very loose and flexible and don't hurt the birds. A bird flies into the net and gets tangled in it. If the bird is heavy enough, it and the mesh it is tangled in fall into one of the pockets of the net. The banders check the nets about every 20 minutes, so a bird isn't tangled for very long. At the end of the morning the nets are taken down and put away so they aren't a hazard to birds. In addition to the nets, the banders set traps at ground level. The traps are kept in place all the time and are baited with seed so the birds know they can get food there. During a banding session the trap doors are allowed to shut on a critter that ventures inside, but at other times the doors are clamped open so animals can wander in and out. This morning we caught a vole in one of the traps. I didn't get to see it because I was with the group of people checking the nets.
But the first bird I got to see was caught in a trap! It was a California scrub jay (Aphelocoma californica) that had clenched its feet around the wire of the cage, making for a difficult extraction. Sophie, the intern wrangling this particular bird, had quite a job of it.
The bird, once extracted from either net or trap, gets put into a cloth bag and taken to an area called The Yard to be worked up. Each bird gets the following treatment:
A complete formal ID, which can be really easy or really difficult
Banded on the left leg with a unique number
Sexed, if possible
Aged and life history stage determined. Age can be guesstimated by examining patterns of wear on the feathers. Missing feathers can indicate either a molt or some recent mishap in the bird's life. Some species are not sexually dimorphic, but females that are incubating or brooding have a patch of bare skin on the front underneath the feathers. Our scrub jay had a brood patch and is thus a girl!
Measured and weighed
The banding itself has to be done by either Martha or Breck. They are the ones with the training required to squeeze tiny bracelets around skinny legs.
It takes practice and skill to hold a bird immobilized but still able to breathe. You also have to avoid the feet, which are equipped with sharp talons. Elizabeth, the intern to whom Martha relinquished this bird for the remainder of the workup, neatly solved the problem of the feet by giving the jay a bag to hold onto. The bird's left leg, wearing the band, is tightly clenched and the right one is grasping the bag.
To examine the skin the handler blows up the feathers. To me this was surprisingly effective. I sort of assumed the bird's down feathers would be too thick to blow through. A good puff blows the feathers up and uncovers the skin.
Birds the size of jays are weighed in bags hung from a spring scale. The scrub jay in its bag weighed 90 grams. The empty bag weighed 15 grams, so the bird's body weight was 75 grams. The weighing was the last part of the workup, and after that she was released. Birds with an active brood patch are probably tending eggs or babies, and should be released in the area where they were caught so they don't have to expend a lot of energy flying back to the nest.
In addition to the scrub jay, we also caught a bushtit and a Bewick's wren. Bushtits can be problematic because they flit around in large flocks, and sometimes 20 or 30 of them will fly into the nets all at once. This results in a frenzy of activity for the banders, who want to work up the birds quickly so they aren't overly stressed. Breck said that while the data are important, the birds are more important, and if they have to let birds go without working them up, then they will. Bushtits are tiny birds--look at how small that wing is!
The last bird we caught was a Bewick's wren (Thryomanes bewickii). These little birds have a reputation of getting pretty tangled in the nets, because when they hit the mesh they start thrashing and making things worse. When I went out with Elizabeth to check the nets we saw the wren wrapped up in the net. It took Martha's expertise to get the bird free, and it screamed the whole time. That's a good sign, as a bird that complains is a bird that is angry rather than scared. Sometimes the net needs to be cut to free the bird, but this time patience and expertise were all it took.
A Bewick's wren is more substantial than a bushtit, although not by much. And it has a tiny leg that requires a tiny band.
And the coolest thing is how they weigh these teensy birds. They're so small that they can fly around inside the bag, which means they aren't confined and would be unlikely to hold still long enough to get an accurate weight measurement from the spring scale. But years ago there was a company named Kodak that manufactured and sold millions of small plastic canisters that probably make up a significant proportion of landfill materials around the world. These little plastic containers happen to be the perfect size for containing the head half of a wren-sized bird, keeping the bird calm so it can be weighed.
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!