Wednesday, January 23, 2013


Deer are the most common large wild mammals that most of us see. The only areas that lack deer entirely are within the city limits of our biggest cities. Any of us who live out in the countryside are likely to have them in our garden, not necessarily a preferred situation.

Two species inhabit the Pacific Northwest, Mule (Odocoileus hemionus) and White-tailed (O. virginianus). Mule occur everywhere, White-tailed mostly in forested habitats east of the Cascades in Washington and northeast Oregon, with a small population along the Lower Columbia River. The latter population is usually listed as a separate subspecies and is of conservation concern.

There are two very distinctive subspecies of Mule in the Northwest, the true Mule Deer (O. h. hemionus) and the Columbian black-tailed Deer (O. h. columbianus). Black-tails are smaller and darker than "muleys" and live in the wetter and more heavily forested areas west of the Cascades crest. They are typically seen at forest edge, although where not harassed they feed well out in open meadows. Mule Deer are common in open woodland and grassland east of the Cascades, drier habitats where their pale coat is more appropriate.

The three types can be distinguished by several characteristics. White-tailed have a long tail, brown above and white below, that is elevated like a flag when one is disturbed and goes bounding away. Mule and Black-tailed keep their smaller tails down. In both, the tail is white below, but in Black-tailed, as the name implies, it is black above, while Mule have the tail base entirely white. Intermediates between these two types are fairly common near the Cascade crests, where they meet and interbreed freely.

Males are larger than females and have antlers in fall and early winter. The antlers serve them to impress other males and keep them away from any female they are protecting as a potential mate. The antlers of Mule and Black-tailed branch dichotomously, with even-length branches, while those of White-tailed have a main branch ("tine") with smaller tines branching off from it.

Deer are generalized herbivores, nibbling leaves from a great variety of shrubs, trees and herbaceous plants, including grasses. A listing of their diets would include all of the common plants in their range except those that are protected by chemicals or serious thorns. Because they are generalists, not many plants in your yard are immune to their incisors.

Most mating takes places in late fall and births in early summer. One young is usually produced, but twins are also common, especially in older female Mule and Black-tailed.

White-tailed Deer have increased and expanded their range, while Mule Deer have declined In Washington state in recent years. As in eastern North America, human land use —both opening up forests and planting trees—seems to favor White-tailed, while our activities in general are less favorable for Mule Deer. Black-tailed Deer are holding their own, probably because their habits are more like those of White-tailed. They are protected in many areas just because they live in close proximity to human neighborhoods.

Dennis Paulson

Thursday, January 17, 2013


The winter of 2012-2013 has seen record number of Pine Siskins (Spinus pinus) in the Pacific Northwest. Numbers in the thousands have been reported on some Christmas Bird Counts. What's going on? It turns out that siskins are cyclic, on the average peaking in a given area in alternate years, and the peaks on occasion are very high. Thus they have a two-year cycle. The cause of this cycle is usually thought to be food availability, which varies in both space and time.

Siskins are among our smallest birds. They are members of the finch family Fringillidae, a family of interest because of its adaptive radiation into the seed-eating niche. The biggest species eat large seeds, the smallest very small seeds, and so forth. Pine Siskins eat a great variety of seeds of weedy herbaceous plants in the summer, but in winter in the Pacific Northwest they are strongly associated with red alders (Alnus rubra).

Alders bear their seeds in small conelike structures, and the slender bill of the siskin is well adapted to extract these seeds. Flocks of siskins visit alder trees and spend quite a bit of time working through the abundant cones. These flocks can be of surprising large size, up to and over 100 birds, but are usually smaller.

Pine Siskins also eat a variety of other seeds, from dandelions to hemlocks, and are frequent visitors to bird feeders, especially preferring thistle seeds. Unfortunately, this can be their undoing, as they seem very subject to infection from salmonella, which is spread in their feces. Birds may defecate while at feeders, and thus the salmonella bacteria are spread from bird to bird. Most winters, people who feed birds report sick and dead siskins at their feeders, sometimes dying right on a feeder.

Pine Siskins are very aggressive little birds. Perhaps they have to be because they go around in flocks, and a bird has to defend its feeding site against others. But they are also aggressive toward any other species, and at feeders, it is an impressive sight to see a siskin chase away a larger finch or sparrow. Siskins often have yellow in the wing and tail, and larger yellow patches may enhance a bird's success in driving away others.

Dennis Paulson

Tuesday, January 8, 2013


We are all familiar with hawks and owls, raptorial birds with strong feet and long, curved talons for capturing and carrying prey and a strong, sharp-edged, hooked bill for tearing that prey into bite-sized morsels.

But there is another group of common birds that are just as predatory, although with somewhat different anatomy. These are the shrikes. Shrikes are members of the perching bird order Passeriformes, and although that order is full of insect eaters (shrikes do this), it's not so full of birds that eat small vertebrates such as lizards, songbirds and rodents (shrikes do this too).

Loggerhead Shrikes (Lanius ludovicianus) are widespread breeders in interior sagebrush habitats in the Pacific Northwest. With us only in the summer, they feed primarily on large insects such as grasshoppers and beetles, but they also eat small vertebrates whenever they can capture them, including voles and birds right up to their own size.

Northern Shrikes (Lanius excubitor) breed in the boreal forest and drop down to the PNW in the winter. They are more widespread than Loggerheads, occurring throughout the region in open country. Although they take many insects on their breeding grounds, Northerns are bird and mammal eaters in the winter. Voles are among their most common prey, but they will chase and capture small birds of any sort.

Shrikes have typical perching-bird feet, not raptorial, and they don't capture or kill their prey with their feet, but they do use their feet to carry prey, especially heavy items and even up to their own weight; otherwise prey is carried in their bill.

Although not just like a hawk's, the bill is strong and hooked at the end. It has a pair of toothlike structures near the tip of the upper mandible (tomial teeth) that are important in prey-killing. The shrike bites a vertebrate just behind the head, and the "teeth" apparently sever or injure the spinal cord sufficiently to kill or paralyze the prey, which then cannot struggle and possibly injure the predator.

Not having feet to hold a prey animal down while tearing pieces of flesh off, shrikes have evolved a substitute. They carry their prey to something on which they can position it. In nature, this would involve impaling on thorns or hanging from crotches where two branches diverge. They can then begin to dismember the prey.

Having evolved this behavior and often taking prey much too large to be eaten in one session, shrikes further evolved the behavior of leaving the prey hanging and returning later to eat some more. Wherever shrikes occur, such prey are liable to be found. Nowadays, we can watch for shrike prey caches on barbed-wire fences!

Dennis Paulson
Nature Blog Network