Wednesday, November 30, 2011


One of the surprises in studies of urban wildlife in recent years is the invasion of our cities and suburbs by predatory birds such as hawks and owls. Perhaps "invasion" is too active a word, and a better word is "acceptance." More and more raptors are apparently becoming comfortable with living in the cities of the Pacific Northwest and, in fact, all across North America.

Bird feeders have become a dependable part of the urban/suburban environment, and many small birds are attracted to them. The juncos and finches and sparrows that abound at feeders attract Sharp-shinned Hawks in winter, but the hawks leave for the mountains in spring. However, their larger relatives Cooper's Hawks are year-round residents, feeding on pigeons, jays, and flickers and nesting in wooded areas that give them a sense of security. The males are conspicuous in spring, with display flights and vocalizations, so more and more of them are being detected living among us.

Merlins too are in the process of becoming city dwellers. These small falcons nest in forests near open country, where they usually capture their prey (small birds). Wintering Merlins probably moved into cities to take advantage of local concentrations of small birds, and eventually pairs remained throughout the year and nested because of that prey abundance. Their nesting efforts have been successful, and the population of urban-nesting Merlins has slowly risen.

Barred Owls have moved into the Pacific Northwest from the north, and they too appear to be comfortable in wooded parts of our cities. Preferred prey include the gray squirrels and rats that have been introduced into the region, and our bird feeders attract and concentrate these mammals as well. There are now pairs of Barred Owls, Cooper's Hawks, and Merlins nesting in wooded areas near my house in Seattle that weren't there 10 years ago.

Red-tailed Hawks do not live around dense housing developments, but large parks and open spaces furnish adequate hunting grounds for rats and squirrels, and if any trees in their territory are large enough to support their nests, they may nest in our cities. Many more of them appear in winter to hunt in open areas around parks and airports.

The Great Horned Owl is a top predator surprisingly willing to live in cities, mostly in relatively large parks. It is large enough and fierce enough to handle mid-sized mammals such as raccoons, opossums, and domestic cats that thrive in cities. Crows and pigeons furnish abundant prey populations as well. Nest sites (usually old Red-tailed Hawk nests) may be limiting, however.

Even more surprisingly, after a long period of decline during the DDT era, Bald Eagle populations have rebounded in the Northwest, and they not only visit but even nest in the cities, often in large parks near water where prey species such as waterfowl and fish are available. They need large trees for their huge stick nests.

Whenever a shift like this occurs, it is worth trying to distinguish between behavioral adaptation and genetic adaptation. Have these birds "learned" that cities are OK? Or are there genes for city living that have become favored? Are there genes for increased tameness, recognition of bird feeders as sources of bird concentrations, resistance to being mobbed by crows? Actually, cities aren't bad places to live for mobile predators such as these, as there may be local sources of abundant food and some of their own potential predators may be absent. Also, the first individuals to accept life in the cities have no competition from others of their species!

Dennis Paulson

Monday, November 14, 2011


In the fall of 2009, a Black-tailed Gull (Larus crassirostris) showed up roosting on a log boom on the east side of Commencement Bay, near Tacoma. It was found on October 13 by Charlie Wright and remained for about a month, seen almost daily until November 7. I remember that date well, as it was seen that morning. That afternoon, Netta Smith and I were finally able to accompany Shep Thorp in his boat, the best way to see the gull, but we were unable to find it. It had presumably headed south with the large numbers of California Gulls that had been present until that time.

In the fall of 2011, presumably the same bird showed up at the same spot. First seen by Shep on September 14, it was still present as of November 4 but may have departed soon after that. During both of its visits, this bird was seen by many enthusiastic observers, mostly at a distance of several hundred yards, spotting-scope range. By far the best way to see it was to go out in a small boat and circle the big log boom on which it roosted daily with hundreds of other gulls.

On November 4, Netta and I brought our kayak down from Seattle and launched it from the Gilmur access point on the bay. Very quickly we found the Black-tailed Gull and captured a few mediocre photos. Then something spooked them, and a bunch of the gulls took off. We saw our bird head across the bay and disappear in the distance, very disappointing. But we weren't discouraged, as the day, although threatening rain, had turned beautiful, with the low afternoon sun illuminating the maple-covered hillside in front of us.

We maneuvered the kayak around the log boom and found a place to enter it, giving us better light for photography. The boom was covered with gulls over much of its length, with photo ops abounding. Double-crested Cormorants roosting on it didn't like us at all, and they took off when we were a hundred yards away. Harbor Seals watched us but stayed put until, in a few cases, we got too close for their comfort level. The gulls just mostly sat and watched us paddle or drift past as close as 30 feet from them. They are surely used to curious kayakers by this time.

The most abundant gulls on the boom were Bonaparte's and Mew, at least several hundred of each. Among them were dozens of California and a few Thayer's and Glaucous-winged. We scrutinized the flock carefully and were able to find no other species. While slowly moving around the boom, we found to our delight that the Black-tailed had returned. We were able to get photo after photo of it as it watched us; it often rested with eyes closed, comfortably napping. When we got a little too close several times, it hopped onto another log, giving us the opportunity to photograph it with a different species.

Among the hundreds of gulls, the lack of immatures was noteworthy. There were no immature Bonaparte's and only a few immature Mew and California, a far lower proportion than would have been in their populations. Obviously immature gulls were not using Commencement Bay, or perhaps they weren't roosting. Do they have a harder time finding enough food and therefore have to continue foraging for a longer time? That makes sense, and the timing of mature vs. immature gulls at roost sites would be an interesting research project.

Another point of interest was the variation in leg color in the adult gulls. We noted such variation in Bonaparte's, Mew, California, and Thayer's, usually from duller to brighter. Bonaparte's varied from pale pink to red-orange, California from yellow-green to blue-gray. Thayer's are supposed to have rather bright red-pink legs, but one adult had very pale whitish-pink legs.

In any case, my luck had changed; it turned out that this was probably the last time the gull was seen!

Dennis Paulson

Thursday, November 3, 2011


Egg laying is a very important part of the life of an insect, as the number and placement of the eggs influences where the larvae that hatch from them will live and how many of its own species it will have to compete with. The presence of other animals that are potential predators on the eggs must also be taken into consideration. Oviposition occurs in two quite different fashions in the dragonflies and damselflies, order Odonata.

Exophytic egg-layers extrude fertilized eggs, often in a clump, through the genital opening in their eighth abdominal segment. The female flies over the water, stopping at intervals to descend to the surface and tap the abdomen in the water, releasing the cluster of eggs. This mode is characteristic of most dragonfly families, for example skimmers (Libellulidae), emeralds (Corduliidae), and clubtails (Gomphidae).

There are several variations on this theme. Numerous species splash eggs onto the adjacent bank in drops of water, perhaps to make the eggs safer from aquatic predators. The larva will find its way to the water upon hatching. Some members of the skimmer family drop single eggs one at a time onto dry land in basins that fill up with winter rains. Their larvae develop during the spring and emerge as adults in midsummer, then hanging around as the pond dries up to lay eggs in the pond basin after it dries up in the heat of late summer.

Others actually deposit their egg masses on leaves and stems above the water, and the larvae drop into the water when the eggs hatch.

Dragonflies of the darner family (Aeshnidae) and all damselflies are endoophytic egg layers, utilizing a quite different oviposition strategy. These odonates have well-developed ovipositors at the end of the abdomen, and they insert eggs singly or in pairs into plant tissues. These eggs are much better protected against predation than the exophytically laid eggs, placed precisely rather than scattered, and fewer of them are laid.

Endophytic ovipositors typically have a clutch size (the number of eggs matured in one batch) of one to two hundred eggs and typically lay only a few clutches. However, long-lived females may lay more clutches, eventually totaling in the low thousands of eggs in their lifetime. Exophytic ovipositors lay smaller eggs more quickly (up to 300/minute in some species), and their clutch sizes are larger, in the thousands, but with lifetime totals perhaps no higher than the longer-lived endophytic species.

Oviposition sites are presumably chosen as good larval habitats, and several egg-laying females will often collect at the same spot, presumably attracted by the ones already there.

Because female dragonflies are a scarce resource at the water, males will always try to mate with them, and in many species, the male stays hooked up to the female with which he has mated through the oviposition process to keep other males away from her. Thus both exophytic and endophytic ovipositors may be seen doing so in tandem.

Dennis Paulson
Nature Blog Network