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Weather conditions: |
Spring melt was early at Old Chevak in 2004. By the time the field crew arrived on 11 May, the tundra was > 99% snow-free in the vicinity of the field station, and by 14 May, all snow was gone. The Kashunuk River was ice-free as of 11 May, the earliest date on record. There were two stints of field work at Old Chevak, 14 May - 2 June, and 9 June - 28 June. Maximum daily temperatures remained above freezing for the duration of the field work. Measurable precipitation (rain and/or drizzle) occurred on 14-18 May, 20-24 May, 31 May, 2 June, 14-15 June, and 17-24 June. No snow fall occurred during entire field effort.
Most severe weather occurred in the third week of May (i.e., during early clutch initiations) when 15-30 knot winds coincided with rain from 16-18 May, and storm broke at noon on 18 May. No evidence that it affected timing of clutch initiations. The first major emergence of flying insects (chironomids) was on 19 May; the first day of major mosquito activity was 1 June.
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| Rodents abundance evaluation: |
low
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Breeding conditions:
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Small numbers of Long-tailed Skuas, including pairs, were seen on the study area on a daily basis. Only one pair actually nested, however (clutch size of 2, successfully hatched). Arctic Foxes and Mink (Mustela vison) were seen on nine and five of 20 field days, respectively, during shorebird laying and early incubation. Up to three Arctic Foxes were observed simultaneously on the 4 km2 study area; waterfowl researchers familiar with the study site indicated that the frequency of fox observations was very high relative to most years.
Field work at Old Chevak focused on the breeding ecology of Bar-tailed Godwits (Limosa lapponica baueri). Potential predators of Bar-tailed Godwit eggs, chicks, and/or adults observed on the study site included Northern Harrier, Golden Eagle, Merlin, Gyrfalcon, Sandhill Crane, Arctic Skua, Long-tailed Skua, Common Gull, Glaucous Gull, Short-eared Owl, Common Raven, Arctic Fox, Mink, Ermine (M. erminea), and Least Weasel (M. nivalis). We observed adult godwits mobbing Northern Harrier (once), Sandhill Crane (once), Arctic Skua (12 times), Glaucous Gull (2), Common Raven (1), Arctic Fox (6), and Mink (2). We also observed adults spooked by a Short-eared Owl, and responding vocally to both a Golden Eagle and a Sandhill Crane.
Twelve Bar-tailed Godwit nests were found at Old Chevak in 2004 through a combination of focal observations and rope-dragging. Seven of the 12 nests were found during the laying period (i.e., prior to completion), two were found with complete clutches, and three were of unknown status because they were found during, or after, predation. Nest initiations ranged from 14 to 30 May; the mean initiation date was 23 May. Estimates of the age of chicks in two additional broods in the fourth week of June suggested that the clutches from which they had hatched were also initiated during the latter half of May, probably near or just prior to the mean clutch initiation date.
All 12 godwit nests found on the study area were depredated. Among those nests that were found during, or survived until, incubation, the mean length of survival after clutch completion was only 4.8 days. The nest surviving the longest lasted only until day 11 of incubation. Arctic Fox and Sandhill Crane were each observed depredating one nest; a third nest was apparently depredated by either or both of these species (based on observations of godwits mobbing both species in the immediate vicinity of their nest on the same morning that the nest was ultimately abandoned with only a single egg remaining). The predators responsible for the other nests losses could not be determined. We observed Arctic Fox, Mink, Ermine, Sandhill Crane and Arctic Skua depredating nests of other species on the study plot. Subsequent to the depredation of known godwit nests, only 2 godwit broods were found that might have hatched from additional nests on the study plot.
The high rate of godwit nest predation was apparently a local and/or species-specific phenomenon. Overall, waterfowl nest success was quite high on the outer Yukon-Kuskokwim Delta in 2004, and although sandpiper nest success at Kanaryarmiut Field Station, 19 km to the southeast of Old Chevak, was below the 7-year mean, it was >45% higher than in either 2002 or 2003.
Ten nests of Grey Plover were also found on the study area. At least seven of the 10 were depredated; the remaining three were all still extant when last checked. Between 18 and 27 May, approximately 80% of the study area (~3.2 km2) was rope-dragged a single time for nests. During this effort, 129 nests of 11 species were located, including 121 nests of seven shorebird species: Grey Plover (2), Bar-tailed Godwit (4), Black Turnstone (Arenaria melanocephala, 1), Western Sandpiper (Calidris mauri, 105), Rock Sandpiper (C. ptilocnemis, 5), Dunlin (C. alpine, 2) and Red-necked Phalarope (Phalaropus lobatus, 2). The 105 Western Sandpiper nests represented 87% of all shorebird nests found during rope-dragging. No other shorebird species exceeded 4% of the shorebird nest total from rope-dragging. These numbers should not be converted to estimated densities, because even multiple visits by rope-draggers only find a fraction of the shorebird nests present on a plot.
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Summary
of fauna studies: |
Field work was a pilot study of breeding ecology in Bar-tailed Godwits. This pilot study had three primary objectives: 1) determine if breeding densities were high enough to support more detailed breeding ecology studies in subsequent years, 2) collect a single godwit egg from each of 8-10 nests for a preliminary contaminants screening, and 3) collect basic breeding biology data on this poorly-known species.
A field crew observed godwits and searched for godwit nests at Old Chevak from 14 May to 2 June, and from 9 June to 28 June 2004. The density of breeding godwits was estimated to be between 1.5 and 3.75 pairs/ km2. Twelve godwit nests were located through a combination of focal observations and rope-dragging. The former tactic was probably more efficient at locating nests. Egg morphometrics were recorded at nine nests, and a single egg was collected from each of those nests for contaminants screening. That analysis should be completed in 2005. All 12 nests were depredated; known predators included Sandhill Crane and Arctic Fox. Two additional broods hatched from undiscovered nests on or near the plot.
The density of birds in the Old Chevak study area is adequate for implementing a detailed breeding ecology study of Bar-tailed Godwits in 2005. The sample size of nests will be increased by expanding the study area, increasing the field crew size, and using focal observations exclusively for nest-finding. Protocols for reducing researcher impacts on nest success will be expanded in 2005. Results of the initial contaminants screening will be used to evaluate whether additional collections are necessary in order to test hypotheses regarding the impact of pollutants on reproductive success.
Reference: McCaffery, B. J. 2004. The breeding ecology of Bar-tailed Godwits on the Yukon-Kuskokwim Delta: Results of the 2004 pilot study at Old Chevak, Clarence Rhode National Natural Landmark. Unpubl. U. S. Fish and Wildlife Service report, Bethel, Alaska. 20 pp.
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