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low
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Breeding conditions:
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The combined frequency of all mammalian predator observations (i.e., Arctic Fox, Red Fox, and Mink) was the second highest during the study. In 2003, Mink, Arctic Fox and Red Fox were observed on 18, 23, and 4 days, respectively. There was no obvious correlation, however, between the frequency of predator observations and wader nest success. For example, during the year of lowest sandpiper nest success (2002), we made less than half as many predator observations as in 2003, and in the year of most frequent predator observations (1999), sandpipers had average nest success. The number of observations of mammalian predators on our study site has not been correlated with our qualitative assessment of rodent abundance.
A very dry winter, a thin winter snow pack, and the very warm April resulted in extensive snow-free tundra when the Western Sandpipers arrived this spring.
Shorebird clutch initiations in heath tundra habitats were the earliest on record. The first clutches of Grey Plovers, Rock Sandpipers, and Western Sandpipers were all initiated in the second week of May. The first Western Sandpiper clutch was initiated on 11 May, nearly a week earlier than the previous early date of 17 May 2002. Overall, however, nesting chronology was not unusually early in 2003. Among Western Sandpipers at our study site, the date of the earliest clutch initiation in a given year is not correlated with mean, median, or peak clutch initiation dates. Mean clutch initiation in 2003 was 1 June (5 days later than in 2002, and just 1 day earlier than the long-term mean), median clutch initiation was 31 May (8 days later than in 2002, and identical to the long-term mean), and peak was 24 May (the same as 2002). Wetlands and low meadows become suitable for nesting later than the uplands because snow melt and subsequent drainage occurs later there. Among wetland-nesting species, the first Dunlin and Red-necked Phalarope nests were initiated during the third and fourth weeks of May, respectively.
Prior to 2002, Western Sandpiper nest density was calculated as simply the number of nests found divided by the study area size (= 16 ha). By this measure, nest density in 2003 was the second lowest recorded to date, 2.81 nests/ha versus a mean of 2.89 nests/ha (range 2.63-3.06) for 1999-2003. The number of nests found, however, is at least partially a function of nest predation (i.e., fewer nests found when predation rates are high). As in 2002, nest predation in 2003 was very high; Mayfield nest success was only 0.13 in 2003, just slightly higher than the value of 0.11 in 2002, and only half of the 6-year mean of 0.27 (range 0.11-0.55). When rates of nest loss are considered, nest density in 2003 may have been as high as 3.37/ha. Excluding re-nests, the calculated density of first nests was 2.77/ha, which may approximate the density of pairs.
High rates of nest loss led to high rates of re-nesting; 29% of pairs that lost nests eventually re-nested (very similar to the value of 35% in 2002). Among clutches which hatched, fledging success (defined as a clutch fledging one or more young) was 43%, compared to 58% and 39% in 2001 and 2002, respectively. As in 2002, when only 4% of clutches produced fledged young, overall productivity on our plot was very poor in 2003. Only 3 of 45 Western Sandpiper nests initiated on our core plot (7%) resulted in fledged young.
We also surveyed 4 randomly-chosen 16 ha plots as part of an international study evaluating the double-sampling approach for estimating nesting shorebird densities. On these plots, we found an additional 62 shorebird nests of five species: Black-bellied Plover (2), Western Sandpiper (30), Dunlin (11), Rock Sandpiper (3), Red-necked Phalarope (16). Overall shorebird nest success on these plots was 36%. At the species level, nest success estimates for the three most common species, Western Sandpiper, Dunlin, and Red-necked Phalarope, were 40%, 54%, and 25%, respectively.
The point estimate of Western Sandpiper nest success on PRISM plots was three times higher than on the core plot. We hypothesize that the difference was primarily a function of differences in nest-marking protocols between the 2 studies (i.e., the PRISM plot nests were not marked); this hypothesis will be tested with empirical assessment of nest-marking protocols in 2004.
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Rodent dynamics:
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| The last peak in arvicoline rodent populations on the Yukon-Kuskokwim Delta occurred in 2000; another is predicted for 2004 (based on a consistent 4-year cycle since at least 1984). In 2003, voles were observed on 8 days, compared to 38 days in 2000, and an average of 1.25 days in the other 4 non-peak years. Winter nests, conspicuous tunneling, and clippings were scarce overall, but locally dense along the edges of some uplands, and, overall, more common than in other non-peak years. We hypothesize that the increased observations of voles and rodent sign in 2003 reflected a population building up toward the predicted high in 2004.
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Rodent species recorded:
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