Discovery of a population of the endangered Red Siskin (Carduelis cucullata) in Guyana

Auk, The, Apr 2003 by Robbins, Mark B, Braun, Michael J, Finch, Davis W

Copulations were observed on three occasions, all in the immediate vicinity of nests. Females assumed a horizontal posture similar to the quivering wing display described above when soliciting copulations. For example, at 0730 on 18 April, after a pair foraged for 2-4 minutes on Curatella seeds they flew a few meters upslope to another Curatella, and a few seconds later the female assumed a nearly horizontal position, while extending and quivering her wings. While in this position, she gave a relatively high-pitched "tee-tee-tee-tee-tee-tee-tee" (M.B.R. recording, MLNS 11824). After a few seconds of such solicitation by the female, the male landed briefly next to her before mounting and copulating for ~3 s. The male then flew about a meter higher in the tree and both birds began to wipe their bills on perches. The female continued to give the high-pitched call and quiver her wings for another 20 s. She then flew into an adjacent Curatella that contained nest 3.

Male-male interactions were intense on 12-16 April throughout much of the study site, but a transect through territorites of at least 9 pairs of siskins on 17 April revealed much less interterritorial conflict. That reduced aggression was noted until our departure on 20 April. For example, on 18 April, M.B.R. observed two pairs foraging together from 1-2 m above ground in a dense stand of the viny Wedelia calycina (Asteraceae). No aggression was observed, even though both pairs foraged within a few centimeters of each other, and at times even probed the same flower bud within a few seconds of each other, for over 15 min (0830-0845 hours). Those two pairs were only 65 m to the west of the pair attending the nest that was discovered a few minutes earlier.

The densely packed territories appeared to be related to a superabundance of food. During our observations, most Curatella had numerous seeds, and fruiting mistletoe (Phoradendron sp.; Loranthaceae) was quite common. In fact, despite extensive searches, we did not find territorial siskins in areas devoid of fruiting mistletoe. Both sexes routinely were observed foraging on those two plants.

During October and November 2000, ~85 km west of the original discovery site, the first signs of possible breeding during that period were observed. At two different sites, daily singing was recorded and males were observed mate-guarding. During that period, siskins appeared to spend more time in semihumid forest, where they were observed feeding on fruit of fig trees (Ficus spp.). By the end of October, Curatella was again flowering and fruiting, and siskins were observed feeding on flower buds and fruit. During both periods, siskins were also observed feeding on grass and herbaceous plant seeds.

Immature plumage and evidence of nesting success.-In April 2000, all birds (n = 85 birds) appeared to be in definitive plumage. In contrast, during late October and early November 2000, at least 16 of 113 individuals identified to plumage state appeared to be immatures. Presumed immature males varied considerably in amount of black plumage on the head, ranging from birds with only a few black feathers (Fig. 3) to some with mostly black heads with a few whitish-gray feathers. Two individuals with mostly black heads had yellow around the base of the hood. One of those males also had a narrow, dull yellow stripe extending ventrally from the near the base of the black hood down to the white of the abdomen and dull yellow in the upper wing coverts. Birds that had entirely dull yellowish heads had a reddish wash on the chest, with a pale orange patch (much less intense than that of an adult female) at the base of the primaries. Other individuals that lacked black in the head completely lacked orange on the chest and on the wings. Coats and Phelps (1985) state that Venezuelan birds undergo an annual prebasic molt beginning in late July and continuing for up to three months. If the Guyana populations follow similar molt schedules, pronounced plumage differences among young males during October and November would presumably represent birds in different stages of transition from juvenal to prebasic plumage.