Kenn Kaufman’s Peterson Field Guide: Advanced Birding, first published in 1990, took on difficult-to-identify groups of birds, such as winter loons, scaup, medium-sized terns, hummingbirds and Empidonax flycatchers.

The book, peppered with Kaufman’s pen-and-ink drawings, was meant to be a supplement to a field guide.

Now over two decades later, a greatly revised edition has been published. It is fundamentally a different and better book than the first edition. But the new edition is still best used as a companion to a standard field guide.

The number of confusing birds Kaufman covers is greatly expanded over the first edition. Informative photographs are included within each group, in lieu of the line drawings of the earlier edition.

One of the greatest strengths of the new edition is the 140 pages of introductory material, compared to only 19 in the first edition.

In this new edition, Kaufman offers a list and extended explanation of 13 principles of field identification. Here are a couple of these:

• “Always use multiple field characteristics.”

• “Consider the condition of the bird’s plumage.”

He then has an excellent section on feather tracts of birds and molting. A sequence of photographs on the movement of feathers on an opening wing of a house finch is brilliant.

In the folded wing, all the feathers one sees are greater coverts, tertials and the tips of the primaries. As the wing unfolds, the other feather tracts become exposed.

Kaufman then presents sample illustrations of some birds (some at rest and some flying) to indicate the different feather types. For each example, a photograph and a line drawing of the bird showing the feather tracts is shown.

Kaufman compares two schools of thought on field identification of birds.

One school relies on “general impressions of size and shape,” shortened to the acronym of giss.

The other extreme is the fine detail approach, where very close study of feathers, bill color and shape and other structures is required to yield a field identification.

In his coverage of the various problem groups, Kaufman uses both types of information to permit field identification.

For identification of swallows on the wing, Kaufman suggests watching them without using binoculars. One can become familiar with the slight differences in flight behavior and the appearance of distinctive marks from varying perspectives. The giss method can work here.

But for gulls, Kaufman advocates the fine detail approach, pointing out that the color of various feathers in the wings, tail and mantle are needed to be sure of an identification.

EASTERN BLUEBIRDS AND TREE SWALLOWS

Tree swallow and Eastern bluebird numbers are building in the state as their migration proceeds.

It’s time to make sure your nest boxes are in good shape.

Tree swallows and Eastern bluebirds compete for nest boxes. How can you increase your chances of bluebirds nesting on your property?

You can take advantage of the fact that tree swallows are intolerant of other tree swallows nesting within 10 yards of their own nest. So, if you put two nest boxes close together, one will not be used by tree swallows and is therefore available for bluebirds.

Bluebirds need quite a bit more space. Typically, bluebirds will not nest with 200 yards of another bluebird pair.

People often wonder if they should remove the previous year’s nest from a box. Eastern bluebirds prefer to reuse an old nest.

For tree swallows, removing an old nest has no effect on whether it will be used by them in the current year.

HORMONES AND SPRING

In mammals, the gonads (ovaries in females and testes in males) remain the same size once adulthood is reached. Not so in birds.

Because of the demands of flight, the ovary (most female birds only have one ovary) or testes of birds are greatly reduced during the nonbreeding season. Why carry around well-developed reproductive structures when those organs are not needed?

With increasing day length, birds start to produce hormones: mainly testosterone in males and estradiol (an estrogen) in females. These hormones cause the testes or ovary to increase greatly in size.

The size of a house sparrow testis increases 500 times in the span of a month or so in the spring!

The huge increase in testosterone causes the males to become fiercely combative with other males.

One behavior common this time of year is to see a male songbird attacking its reflection in a mirror or window.

Testosterone levels will decline in due time and the males will become less hyperactive.

 

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]