The Nesting Span in the Southern Willamette Valley, Oregon
The Nesting Span in the Southern Willamette Valley, Oregon.-Gullion in his Birds of the Southern Willamette Valley, Oregon (Condor, 53, 1951: 129-149) bases the dates given for the breeding season on the earliest observed nest building at one end of the season and, at the other, observations of fledglings incompletely feathered or being cared for by their parents. This method ought to result in a considerably greater spread of dates for the season than the method of taking into account only eggs or young found in the nest. Actually he reports a season that is for many birds either shorter or later than egg dates reported for them in neighboring Pacific Coast areas both to the north and south.
For example, his dates for the Western Tanager are June 6 to 19 (so short a period as not to cover a single nesting), whereas Gabrielson and Jewett in the Birds of Oregon (1940) mention eggs taken in the southern Cascades from May 13 to June 27. They say the species begins to build its nest soon after its arrival in Oregon in late April. I saw fully fledged young of this tanager being fed on July 27,1951, in the valley, close to Eugene.
Gullion gives nesting spans for eight warblers known to nest regularly in the area, beginning of course with nesting activity before egg-laying. A check shows that for seven of these eight, earlier dates than his are reported for eggs both by Gabrielson and Jewett (1940) and (at various localities in Washington and California) by Chapman in The Warblers of North America (1907). For most of the warblers Gullion’s first-of-season dates are later by a month or more than a month ; for one warbler they are later by more than two months. This discrepancy is doubtless due to a relative lack of observational data for the southern Willamette Valley as compared with regions more thickly populated with bird observers.
For the other end of the warbler breeding season, Gulliop’s dates also run consistently later (as they might be expected to do) than those given by Gabrielson and Jewett and by Chapman.
I can offer some additional records, all from observations made in the year 1951, which will somewhat extend for a few birds the recorded season in the southern Willamette Valley.
Yellow-breasted Chat (Zcteria sirens). A completed clutch of three eggs was found on June 10. These were discovered on a second attempt to find the nest days after I had become certain that the nest was in a certain blackberry thicket. The three young birds flew from the nest together when I approached it on July 1 and, I believe, did not return to it at all. I am inclined to believe that nesting activity by chats often begins early in June here.
Black-headed Grosbeak (PLezrcticw melanocephalus) . A nest of this year’s building first noticed on June 5 contained a full clutch of three eggs when visited a second time on June 10.
Violet-green Swallow (Tachycineta tholussina) . Adults were still bringing food to a nest box on the morning of July 24.-C. R.‘B. COMBELLACK, Eugene, Oregon, September 13, 1951.