White-winged Diuca Finch nesting on Quelccaya Ice Cap, Peru

Wilson Journal of Ornithology, The, Sept, 2008 by Douglas R. Hardy, Spencer P. Hardy

Some birds are well adapted to environments which are seasonally dominated by snow or sea ice, but birds are not generally associated with glaciers. Only the Emperor Penguin (Aptenodytes forsteri) is known to routinely nest on ice, typically frozen sea-ice (i.e., fast-ice) but at times in association with ice shelves derived from glaciers (Kooyman 1993). Transient birds have been observed passing over mountain glaciers at high elevations outside the polar regions or discovered after succumbing to harsh environmental conditions (Krajick 2002; L. G. Thompson, pers. comm.). However, glacier surfaces are usually cold, actively changing through accumulation and ablation, and at times wet; conditions that are poorly suited for nesting and raising young birds.

The ornithological literature contains only one detailed account of nesting on a glacier. This was the unusual circumstance where glaciers advancing into Alaska's Prince William Sound overran a Black-legged Kittiwake (Rissa tridactyla) colony (Irons 1988). Previously-used nest sites were unavailable and 77 kittiwake nests were constructed on the glacier face. All of these nests failed due to ablation and/or meltwater runoff which either dislodged the nests or caused them to disintegrate (Irons 1988; D. B. Irons, pers. comm.).

The objective of this paper is to present evidence of nesting by White-winged Diuca Finch (Diuca speculifera) directly on glacier ice of the Quelccaya Ice Cap in Cuzco Department, Peru (14[degrees]S, 71[degrees]W). Observations were made over several years during the Austral winter (Jun-Jul) in the course of conducting glacier and climate research on the ice cap. This is the first well-documented case of high-elevation avian nesting on a glacier, corroborating a second-hand report of "ice cave" nesting by White-winged Diuca Finch (Johnson 1967).

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OBSERVATIONS

During June 2005, while exploring the retreating Quelccaya Ice Cap margin, we came upon a nest which appeared to have fallen recently from the glacier (within weeks-months). Several other older nests were observed nearby including one in a cave under the ice margin (Fig. 1). More extensive nest searches were conducted in 2006 and 2007 along ~1,500 m of glacier margin, resulting in location of numerous nests. Most were along two sections with respective lengths of 350 and 530 m, elevation ranges of 50 and 100 m, and upper elevations of 5,200 and 5,300 m. Searches were restricted to this 1,500 m section; the extent to which this is representative of the Quelccaya Ice Cap is unknown. However, nesting on the ice cap has likely not been limited to the last 3 years as L. G. Thompson has occasionally observed nests over the past ~30 years (pers. comm.).

Nest remains were most often found on rocks at the base of near-vertical sections of ice margin. At least 14 nests were found in 2006 and at least 16 in 2007. These varied in apparent age from weeks (i.e., previous breeding season) to several years and the 2007 count almost certainly includes some found the previous year. Two of the freshest nests in 2006 were only 3 m apart.

Typically, sections of glacier margin with nest remains were nearly vertical, somewhat grooved or fluted, and ~5-10 m high. Overhanging icicles and steeply-sloping rock below the margin made access to some nest remains difficult, and nests still attached to the glacier could have been overlooked. One nest was found on the glacier 22 m from the margin, below a steep, step-like section of ice (i.e., not in situ).

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Some nests were entirely intact when found, while others were disintegrating or partially buried by sediment; however, almost all nests were not in situ (cf. Fig. 1D). Net retreat of the ice margin is roughly 1 m/year or more along this part of the Quelccaya Ice Cap and nests constructed on the steeply-sloping margin could only be observed in situ within a brief interval following construction (i.e., breeding season) prior to falling. Evidence for this interpretation is that several nests were found in inverted position and, in almost every case, a vertical trace of nest material was observed above the nest remains, frozen to the ice.

Remains of varying ages indicate multi-year occupation of favorable sites along the ice margin suggesting that reproductive efforts on the ice cap are successful. In addition, we observed fecal sacs in one of the fresh nests, presumably from nestlings just prior to fledging. No off-glacier nesting evidence was found despite searching areas adjacent to the glacier.

Several nests appeared entirely intact and the following is based upon one of the freshest-appearing nests observed in 2006. Nests were bulky structures of grass and twigs with a deep, well-made inner cup (Fig. 2). It appears that a rough platform is initially constructed (32 x 18 cm), which roughly tapers upward and becomes increasingly well-woven towards the top (13 cm outer diameter). Only this better-woven upper portion was found in some cases. The inner cup measured ~6.5 cm in diameter and was 4.6 cm deep. Overall dry mass of the nest (Fig. 2A) was 160 g. Nests consisted of woven grass (~80-90%), particularly the locally abundant Calamagrostis chrysantha. The inner cup was lined with finer grass and feathers were observed in or adjacent to some nest remains (Fig. 2B). Analysis by Carla Dove at the Smithsonian Institution revealed feathers of Rufous-bellied Seedsnipe (Attagis gayi), Andean Goose (Chloephaga melanoptera), and tail feathers of White-winged Diuca Finch. This diverse assemblage suggests that nests are lined with feathers recovered from the surrounding landscape. No evidence of camelid fleece was seen in any nest (cf. Johnson 1967).