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

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

We began operating an automated weather station (AWS) in 2003 at the ice cap summit, ~3 km east of the nest sites and ~500 m higher in elevation. These data permit a close approximation of the climate in which nest building, incubation, and rearing of nestlings occurs on the glacier.

Pronounced seasonality of precipitation at Quelccaya typically features considerable and frequent snowfall from late September to early-mid April. During this wet season, 2 m or more of snow accumulates at the ice cap summit but, at the slightly lower elevation margin, ablation predominates; meltwater flows off during the day and freezes at night. Some precipitation at these nest sites (5,150-5,300 m) may be in the form of rain, as they are close to a rising atmospheric freezing level (Thompson et al. 1993, Bradley et al. 2006). This would impact the bird's exposure to moisture, thermal regulation, food availability, and other factors, and the viability of glacier nesting in the area.

Diurnal fluctuations in air temperature at Quelccaya are greater than the annual variation. By assuming a constant environmental lapse rate, summit AWS measurements can be adjusted to the elevation of nesting site, revealing average daily minima of -3.1[degrees] and -6.3[degrees] C during the wet and dry seasons, respectively. Thus, air temperature is low during the night throughout the year with extreme radiational cooling whenever cloud cover is low (especially in the dry season). Maxima for the same periods reach 2.9[degrees] and 0.9[degrees]C at the nesting sites.

Successful nesting in this dynamic environment and extreme climate requires not only thermal and mechanical adaptations to the ice substrate, but also careful timing within the seasonal cycle of climate. The AWS data suggest that Quelccaya glacier nesting by White-winged Diuca Finch most likely occurs as the wet season concludes in April when nesting sites become exposed and drier, as the transient snow line elevation rises. Daily mean temperatures decrease after March as decreasing cloud cover results in colder nights, but the decrease in daily maximum is considerably more gradual until June (DRH, unpubl. data). Young finches had apparently fledged in each of the past 3 years by this date.

Note Added in Proof--Quelccaya fieldwork during June 2008 provided additional observations. The first nests clearly in situ were observed on the glacier, in locations and orientation as hypothesized. One contained two abandoned eggs consistent in size and color for White-winged Diuca Finch (Johnson 1967). Also, a single off-glacier nest, similar to that described above, was found in situ under boulders ~500 m from the glacier. A late-afternoon gathering of 20-30 White-winged Diuca Finch was again observed, 30-60 min prior to sundown, at the same section of fractured glacier margin where this behavior was observed in 2007. Several roosts were located nearby, all entirely within (vs. beneath) the glacier. One expedition member observed and photographed White-winged Diuca Finch roosting at the site prior to sunrise (J. A. Castaneda Gil, pers. comm.). Supplemental material on glacier-nesting White-winged Diuca Finch at Quelccaya Ice Cap is available at http://www.geo.umass.edu/climate/quelccaya/diuca.html.>