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I?iA. I9O 3 I THE CONDOR 73 type of r?orcor, i and unusually narrow in its streaking. But in this ease, the small size of the California skin at once distinguishes it. The same example also very closely resembles a skin from Delavan, Wisconsin, and one from East Providence, Rhode Island, both of which are un- usually lightly streaked for?sliva. The Rhode Island skin (No. ?6?3, Coil. T. J. H.) is also smaller than the eastern average, so that the differences in this instance I confess to be not obvi- ous. But this only goes to show how the normal range of variation in two subspecies may result in close resemblances in certain individual eases. And this is exactly what must be expected where the degree of difference is not greater than the normal range of individual variation. Among the females the color differences appear even more constant. Among thirty examples of brewsleri there are none so yellow as to be comparable to any of my ?sliva. But the available series of the latter (thirteen) is altogether too small to make a conclusion at all satisfactory. The yellowness of females from the Rocky Mountains and eastward holds in all the examples at hand as a distinguishing character from Caiifornia birds. But in each series there is considerable vari- ation, and it would not be surprising if overlapping of characters would be found in larger series. Discrepancy in size ought still to offer a valuable criterion in the great majority of specimens. Out of the present series (one hundred and sixty in all) only about three per cent of specimens are not with certainty identifiable without reference to locality. The average differences are per- ceptible at a glance to any one. I therefore recommend that the California yellow warbler re- ceive recognition in nomenclature along with the many already accepted subspecies of the same rank. Nesting Dates for Birds in the Denver Districts Colorado. BY FRED M. DILLE. OON after I began the exchange and barter of "bird eggs" at Greeley, Color- ado, in ?88?, I noticed that altho the data coming from the East was nicely written and arranged according to the rules of "Lattin's Hand-book," the dates of collecting for allied species were not good guides for me in my raids about my own locality. The Colorado calendar appeared to be later than the Eastern by from one to four weeks. I therefore began to list my results as to sets, their state of incubation and date of collecting, which list thereafter made my finds -much more satisfactory. After moving to Denver in ?89?, I continued my work on the list, and it was found of much service by friends coming from the East who wished to do some collecting, and who realized after experiencing a good snow storm in May that their Eastern knowledge would not benefit them much here. I hope therefore the publication of these oological secrets will prove of value to all new comers. For I know that, if we Colorado boys were to try our luck in Cali- fornia or Maine, we would lose much time if we could not get help of this nature. The first aim of an oological collector is to find his sets full, as to the nmnber of eggs, and at the same time lacking incubation. The next plan is not to waste your time beating about for meadowlark's nests when the killdeer and her nest de- mand it. These points are the gist of the list. I have bunched the varieties as much as their averages will permit, and from the time that collecting becomes in- teresting I have put them one week apart. Collectors who are employed in banks, offices, etc., will perceive the utility of this arrangement without more disclosure. The first criticism I expect will be to the effect that some one has taken a set of 8 magpie, fresh on April 15. So have I, but I have also taken 553 sets of mag- pie and the date given on the list has given the best results. Most all of these dates are therefore the result of much collecting and many years work. I have