The literature on breeding of Pine Grosbeaks (Pinicola enucleator) is scant, probably because the birds are seldom common even in their known breeding range. The writer was afforded an unusual opportunity in the summer of 1953 to witness the activities of these birds in the breeding season in the Uinta Mountains of northeastern Utah, and from June 10 until July 30, 1953, observations were made almost daily at 10,500 feet elevation approximately 20 miles east of Kamas, Summit County, Utah, and in adjoining portions of Duchesne and Wasatch counties. Rocky Mountain Pine Grosbeaks (P. e. montana) were regularly seen and twelve specimens were collected during this period. The two dominant trees in the region are Engelmann spruce, Picea engelmanni, and alpine fir, A bies lasiocarpa. In an extensive wet meadow Carex was dominant. Upon first arrival at the area on June 10 there was a uniform cover of snow at least three feet deep. Local drifts were, of course, many times this depth. The first Pine Grosbeaks were seen on June 11 when a red male and a typical female were seen feeding with a mixed flock of birds composed of at least a dozen Red Crossbills (Loxia curvirostra), two Pine Siskins (Spinus pinus), a single Gray-headed Junco (Junco caniceps), and a single male Black Rosy Finch (Leucosticte atrata). These birds were feeding on the snow among scattered debris of the spruce trees. On June 15 a male grosbeak was collected and found to have enlarged testes (11 mm.). On June 20 another male had testes measuring 12 mm. On July 4 a nest was found containing two young. The young were last seen in the nest on July 14. Juveniles accompanied by adults were collected on June 30 and July 13. The bird taken on the former date was still being fed by a parent. After the latter date young birds were frequently seen. From these records it appears that the breeding of Pine Grosbeaks in this region begins, on the average, by the end of the first week in June and the young are out of the nest after the first week in July. There is considerable variation, however, some individuals beginning prior to this time and some carrying over to a later date. Twomey (Ann. Carnegie Mus., 28, 1942:461) recorded Pine Grosbeaks in this area as being in postnuptial molt when he was there July 17 to 20, 1937. In two instances he saw adults feeding fully developed young. The seeds of the Engelmann spruce seemed to be the main food for adult Pine Grosbeaks. In all specimens examined except one, spruce seeds were present. In one exception the esophagus was filled with tender new growth from the tips of spruce branches. Of three filled gular sacs examined, one contained 100 per cent spruce seeds, the second contained primarily spruce seeds with some new growth, and the third contained primarily seeds of Silene acaulis with some spruce seeds and insect parts. The young birds are probably on a diet of seeds by the middle of their nest life. On one occasion a pair of birds was seen eating the ovaries of glacier lilies, Erythronium grandiflorum. Gular sacs in small passerine birds have been reported previously for only one species, Leucosticte tephrocotis (see Miller, Condor, 43, 1941:72-73). It was no surprise, then, when s-imilar structures were found in the Black Rosy Finch. However, it was found that the Pine Grosbeak also makes use of such a special food-carrying device. This first came to my attention on June 30 when a male was collected. This bird had the throat very much distended with food. When skinning the specimen it was found that the structure was the same as that in the Leucosticte. Comparison of sketches from my field notes and of preserved material with Miller's figure (op. cit.) show that the structure is identical in the two genera. When fully distended in the Pine Grosbeak the sacs extend far
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Mar 1, 2001
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