Mother Nature's art gallery

Among the many signs of seasonality, one of the most spectacular is the display of beautifully colored leaves that tells us that the season must be autumn. This painting spree by Mother Nature lasts for one or two months and then is gone. When a child asks why the leaves change color in the fall, the question ranks right up there with "why is the sky blue?" It's one of those things of the world around us that we accept without questioning, unless we're a child or a scientist set on finding the answer.

Botanists have figured out how this works. As the days become shorter, plants with deciduous leaves stop producing the green pigment chlorophyll, and the chlorophyll already present in the leaves begins to break down. Carotenoids that have been present as insoluble pigments in the plant's chloroplasts are then exposed as the bright yellows that we see in cottonwoods and aspens and bigleaf maples.

The brilliant reds are produced quite differently. The autumn drop in temperature reduces the transport of sugars out of the leaves, and in some trees the excess sugar is used to synthesize anthocyanins, the same pigments found in red flowers. This happens in our vine maples, our blueberries, and our mountain ashes, among others. A combination of anthocyanins and carotenoids produces the range of colors that we see in many species.

Even knowing the "how," have we answered the "why?" Is there any advantage to a plant in having these colors in its leaves in the fall? That question remains to be answered. Perhaps this particular phenomenon has no adaptive significance. But perhaps it does!

Autumn is a time during which nature can be enjoyed at a distance; just look at forests or tree groves or individual trees in a park. In New England, the whole world changes color. In the Pacific Northwest, the brilliant reds and yellows of the deciduous trees are scattered through landscapes of evergreen conifers.

The color change is very different in different groups of plants. Red alders are prominent in our Northwest forests, but they contribute nothing to the fall extravaganza, the leaves merely turning brown and then dropping from the tree. This leaves many of our westside forests rather dull except for bright spots of red vine maples and yellow cottonwoods. For total immersion in autumn colors, a resident of the Puget Sound area should head into and east of the Cascades.

Dennis Paulson

Winter hummers

It's late September. Got a hummingbird in your yard?

Most people think of hummingbirds as tropical, and indeed most of them are. But a fair number of species have moved quite far north into the United States (including Alaska!) and Canada since the last glaciers receded. The Southwest has a great diversity of species, as many as 15 species breeding north of the Mexican border. But many of the border species migrate south for the winter, and all that occur north of the border region are migrants to Mexico and beyond, except one—Anna’s Hummingbird (Calypte anna).

This species was historically resident in southern and central California and northern Baja California, areas that remained warm enough in winter that the birds could remain through the cold season and find enough insects and winter-blooming flowers to sustain them. But that was then, and this is now. Over a half century ago, people discovered they could attract hummers to their yard by hanging out special feeders filled with sugar water, typically one part sugar dissolved in four parts water. It worked like a charm. People feed hummers all over North America now, and birders gather to watch these birds at southern localities with dozens of feeders and, sometimes, hundreds of hummers. These sites are especially rich during fall migration, as hummingbirds are streaming south through the western states on their way to Mexico.

All species may have benefited from the existence of these feeders, but none more than Anna’s. This species has extended its breeding range all the way north to southern British Columbia and east to the Arizona-New Mexico border, with occasional breeding attempts even outside this range. Nonbreeders have wandered east as far as Minnesota and Florida and north to southern Alaska.

Several other species of hummingbirds (Black-chinned, Rufous, Calliope) nest widely in the Pacific Northwest, but all except Anna’s leave in late summer and head for Mexico, not to return until the following spring. Anna’s is supremely adapted to live with people, taking advantage of nonnative plantings and feeders in a way the other species have not been able to do, and this has allowed it to overwinter in regions apparently too cold and/or food-free for the other species. All hummingbirds go into torpor during low temperatures at night, so why can’t the other species take advantage of feeders that are provided throughout the winter? Perhaps the fact that Anna’s was resident in the first place, with no genes for migratory behavior, allowed it to be perfectly adapted to take advantage of the changes we make in the natural world.

Dennis Paulson

it's sparrow time!

It’s September, and the days are getting shorter at great speed. Today is the first day of fall, notwithstanding that the temperatures will be in the 80s in the Puget Sound area. Bird migration has been in full swing for almost three months, and most of the insect-eating birds have moved on southward. But the sparrows are still passing through at this time, some heading as far south as Mexico, others intending to hang around our area.

Why are there so many sparrows? Simple answer is that they eat the small seeds of small plants, and there are an awful lot of small plants out there. The seeds of many herbaceous plants are formed during the summer or fall, then hang around at or near ground level before sprouting into young plants the following spring. Before that happens, however, there is a whole winter of predation ahead of them and a whole array of predators lurking to pounce on an unsuspecting seed.

Insects eat the seeds, chipmunks and mice eat the seeds, and birds eat the seeds. Predominant among the birds are our native sparrows. Song Sparrows are probably the most common, but there are lots of wintering White-crowned, Golden-crowned, and Fox Sparrows as well, with smaller numbers of American Tree, Savannah, and Lincoln’s Sparrows.

Although not sharing the name, Dark-eyed Juncos and Spotted Towhees are common wintering birds also closely related to the native sparrows. In fact, all of them are closely related to the Old World buntings, and we should have called them buntings when common names were coined for them several hundred years ago. But we didn’t. Instead, we co-opted the name of an unrelated European seed-eating bird, the House Sparrow.

As all of these small birds eat small seeds, how do they avoid intense competition with one another? Turns out that each sparrow species has its own habitat preference, which means they’re not all feeding in the same place. Savannah Sparrows like open country and live and feed happily among grasses. American Tree, Golden-crowned, and White-crowned Sparrows like to feed in the open but need dense shrubbery to retreat into when threatened or spending the night. Song, Fox, and Lincoln’s Sparrows prefer dense shrubbery all the time, although they will often come out to the edge where they can be seen by birdwatchers.

Many of us—in fact, hundreds or thousands of us—feed these birds, putting out millet and mixed bird seed on the ground or in feeders, and they respond readily. If you’re lucky, you might have most or all of these species at your feeder if you live in the suburbs with good plant cover around your house. Watch them with binoculars to see how quickly and efficiently they crack and eat those seeds.

Dennis Paulson

Scoter wrecks and risky molt strategies

The scoter wreck or strandings on the outer Washington coast at Kalaloch and La Push has received attention in the media and birding email. I spent 16 Sept 2009 surveying beaches and collecting specimens for the museum. I visited six beaches and encountered 166 beached birds including 83 Surf and 65 White-winged Scoters (see TABLE) (Photos 1-3). Unreported in media and related information was that all the scoters were in wing molt. This realization first hit me while standing in the dawn drizzle with crashing surf and a line of dead scoters visible along the beach in the dim light. Since then I’ve been mulling over the question, why were the scoters attempting to molt on the open coast?

Molt in scoters and many seabirds is a simultaneous molt. All flight feathers are lost and grown in a 3-4 week period. Unlike sequential molt, which allows birds to retain the ability to fly, birds are flightless during simultaneous molt. Body molt is also ongoing, resulting in lessening of the protective cover afforded by the body feathers, which can lead to loss of buoyancy and hypothermia. Molt timing and strategies evolve so that birds minimize risks during the period when flightless. Presumably molt staging areas are located in protected areas with plentiful food. However, on the outer coast it would seem that flightless birds would be continually hammered by the crashing surf and rocks in the shallow water they need for feeding. The protected waters of Puget Sound or Straits of Georgia would seem to be safer molting areas. From what I gather, there are few baseline data regarding the distribution of migrating scoters for the outer Washington coast, so it is unclear if the beached birds were indicators of an unknown staging area used for molt during migration, or if their presence was an anomaly, perhaps related to ENSO (El Nino/Southern Oscillation) that is developing in the Pacific.

A few known facts about scoter migration come from Birds of North America accounts. Molting areas are known for the coasts from Alaska south to BC. After females lay eggs, male scoters start moving to molting areas followed by females after scoterlings fledge. Juveniles are last to migrate and appear to skip molting areas and do not undergo wing molt. Notably, the beached birds were mostly adult males and there was only one juvenile. Using molts scores, I will be able to estimate the onset and completion of molt for this group which will provide significant data regarding timing of molt. In addition all the dead birds appeared to be emaciated, which can be confirmed from examination of salvaged specimens.

Based on existing distributional data, it appears the birds were too far south, but perhaps they have just been missed because of insufficient surveys. Reportedly there was a combination of high surf, tides and wind over Labor Day weekend and beached birds started showing up two days later with peak numbers 3-4 days after Labor Day. The scoters might be doing a normal molt migration, but were trapped by the storm and forced ashore. It is also possible that ENSO has altered the ocean conditions or currents. Birds might have started molt at the normal time and place, but because of altered currents, they did not follow normal routes. The general consensus is that feeding is necessary during molt because molt is energetically costly. Perhaps they arrived in poor condition with insufficient reserves to make it through the molt, and their condition was exacerbated by the Labor Day Storm.

Another factor that could have caused mortality and is being tested is that an algae bloom resulted in a red tide and paralytic shellfish poisoning (PSP) which could kill birds outright. Indirect mortality can also result. The dinoflagellates associated with red tide can also produce a compound that is whipped into a foamy surfactant (soap) by the surf. This foam washes protective oil from feathers leading to loss of buoyancy and hypothermia, and birds come ashore as they attempt to cope. That latter mechanism, discovered in 2007, was the cause of stranding and mortality in Monterey Bay, California. However, I found none of the signs of surfactant-mediated mortality that were detailed in the original paper. There are many factors that could have contributed to the wreck, and my speculation highlights how little we know about some of the common bird species in the Northwest.

Gary Shugart

where have all the birds gone?

I have perceived a lack of songbirds lately, and you probably have also. Not only did birds stop singing at the end of their breeding season, but most of them departed for parts unknown.

Where do these multitudes of birds go? You have to answer this question for each species, as each species has its own unique distribution. But we don't know where each individual goes, and when a Barn Swallow flies by me, I fantasize about it carrying a little flag that says "on the way to Bolivia." The great mobility of birds has long been recognized as one of the most characteristic things about them, and they use this mobility to good avail in their annual migrations.

By migrating north in spring, birds that have wintered in the tropics can take advantage of a seasonal flush of food resources, avoid competition with the great diversity of resident species, and get away from the nest predators—among others ants, snakes, kinkajous, and toucans—that are so common in the tropics. When winter comes at our high latitude, and insects and other primary sources of food are no longer available, they return whence they came.

Some of our breeders, for example Varied Thrushes that dig insects from the forest litter and Dark-eyed Juncos that subsist on weed seeds, may winter in the Washington lowlands, just downslope from where they bred. Seed-eating birds such as finches and sparrows often winter quite far north, as there is an abundance of seeds—the plant's dormant stage—at that season. So our backyard winter avifauna features seed-eaters, and many of our breeding sparrows winter not far away, in California and the Southwest.

But the majority of our small birds are insect-eaters. These birds—the thrushes, sparrows, vireos, warblers, tanagers, flycatchers, and swallows—head for warmer climes.

Many birds glean caterpillars and other insects from leaves. Leaf-eating insects become inactive at low temperatures, and leaf-gleaning birds can't find enough food to keep their metabolic furnaces stoked, so off they go. Most of our vireos and warblers winter in western Mexico and northern Central America, as do Western Tanagers, Black-headed Grosbeaks, and Bullock's Orioles.

Flying insects are even less likely to be active during winter, as they need real warmth to be able to fly. So those birds that eat flying insects can't make a living anywhere near these parts, and many of them are long-distance migrants. Western Wood-Pewees and Olive-sided Flycatchers head for the mountains of Central America, Bank and Cliff swallows and Eastern Kingbirds to the Amazon Basin, and Barn Swallows rarely make it all the way to Tierra del Fuego. These are long flights, but ones quite possible to long-winged birds such as swallows.

They’re gone but not forgotten, and they will return. Of course they leave behind many resident birds such as chickadees, jays, woodpeckers, and others, but that's another story.

Dennis Paulson

why poisonous fruits?

This is the time of year in the Pacific Northwest when many wild fruits are evident, their conspicuous colors standing out against the green landscape. Most of them are eaten by birds, but some of them are toxic to humans, for example, red elderberry (Sambucus racemosa), red baneberry (Actaea rubra), and deadly nightshade (Solanum dulcamara). Why can birds eat these fruits and we (and often other mammals) can’t?

Here we have to deviate from known facts and move into the speculative realm. In other words, we know what but we don't know why. But this is a subject about which I have speculated for many years, since I was first told about a poisonous blueberry (Pernettya) in the mountains of Costa Rica.

We all know that bright fruits are intended to attract and be eaten by birds, their seeds defecated out at some other time and place. This is the way these plants get their seeds dispersed.

It would seem that it is in a plant's best interest to have its seeds dispersed at some distance from the parent plant to avoid competition with it for light, water, and nutrients. Thus birds, with their great mobility, should make excellent seed dispersers. Mammals are just as fond of fruits as birds are, but they are not so mobile and are probably less effective at dispersing seeds. Therefore, we might expect some plants to evolve mechanisms to discourage mammals while at the same time encouraging birds.

I consider this a likely explanation of the many kinds of fruits that are eaten by birds but poisonous to some or all mammals (including humans). Birds and mammals have a long independent evolution, and it would not be surprising to find compounds that were toxic to one group but not the other.

I am inclined to extend this reasoning to account for two other types of plant adaptations. Many plants produce skin-contact poisons, and all the ones I know about produce edible fruits and bird-dispersed seeds. Poison ivy is a good local example. This might also be an adaptation to keep mammals away from their fruits.

Finally, think of all the spiny shrubs that produce edible berries, for example blackberries and roses and gooseberries. Might this not be still another way to keep those hungry mammals away? The common wisdom is that spines protect the leaves from potential herbivores, but why not question the common wisdom? Remember, a mammal has to climb into a plant, while a bird can fly in and out without a scratch.

The only data I know of to support this hypothesis comes from a study of chili peppers (Capsicum) in the Southwest conducted by Don Norman, Seattle ornithologist and toxicologist. Mammals shunned the fruits while birds ate them avidly (perhaps birds always eat avidly). There is much more material here for PhD dissertations. The fact that the poisonous baneberry produces both bright red and white berries is surely a fascinating natural-history story of its own. And why does red elderberry have a black-fruited subspecies at high elevations in the Northwest?

Dennis Paulson

feeding birds

People often ask me whether feeding birds is good or bad. Perhaps it’s both. I feed birds because I love to have them in my yard, not because I think I’m doing them a great favor. In the lowlands of the western part of the Pacific Northwest, perhaps the only time we really aid birds by feeding them is when snow covers the ground, making it difficult for some species to find food. That’s when I see species at my feeders that I didn’t even know were in the neighborhood. Varied Thrushes and Fox Sparrows are two good examples.

Normally, natural selection eliminates the least capable individuals from a population during hard times, and by our feeding them this winnowing may not take place. It may even boil down to helping individual birds to the detriment of the gene pool of their species. So when we make bird populations increasingly dependent on our handouts, we may be obliged to continue feeding them. Birds that normally winter in the tropics may take up residence at a feeder in the fall and not migrate south; they will probably be in trouble if the feeding is discontinued. Many birds (for example, Anna’s Hummingbird in the PNW) have probably expanded their winter range because of dependable bird feeding.

However, there is also a downside to bird feeding. Cats haunt the shrubbery and accipiter hawks visit from time to time; birds kill themselves against windows; and disease spreads readily at feeders. All of these sources of mortality are there without feeding, but the concentration of birds at feeders exacerbates them.

And then there is our subsidy of introduced species. I live next to a green belt in Seattle, with a nice variety of birds, but starlings often dominate the suet in summer and House Sparrows the seed feeders all year until a recent and surprising decline in both species in my neighborhood (lack of nest sites?). 


When Rock Pigeons visit, all too frequently, they easily displace native Band-tailed Pigeons. Millet feeders attract cowbirds, which parasitize native passerines, although cowbirds have also declined dramatically in Seattle. And don’t forget the gray squirrels and rats that compete with the birds (and eat their eggs). I don’t know any way to avoid this when feeding birds.

The feeding of waterfowl at parks is even worse, leading to the proliferation of semidomestic ducks and geese, as well as pigeons and sparrows. Diseases transmitted by these birds will of course infect wild populations. Birds of the native species are quite able to find their own food, but some of them become virtual beggars, a far cry from the traits for which we admire them!

It sounds as if I’m arguing against it, but in fact bird feeding at our homes is probably benign for most birds and furnishes much pleasure, as well as personal education, for us. There is also greater knowledge of the birds when their occurrence is recorded on Cornell University’s FeederWatch (http://www.birds.cornell.edu/pfw/) or  ebird (http://ebird.org/content/ebird/). In any case, the real favor I think we can do for birds is to fill our yards with plants that attract insects (just the opposite of the gardener’s strategy), bear edible fruit and bird-pollinated flowers, and/or furnish good nest sites. And lay off the pesticides.

Dennis Paulson