Population ecology of the long-billed curlew (Numenius americanus) in Western Idaho

-In western Idaho, a breeding population of Long-billed Curlews (Numenius americanus) remained relatively stable over a 7-yr period. Productivity was monitored closely from 1977 through 1979. Clutch mortality rates did not differ significantly among years, and mean clutch survival for a 32-day nesting period (4 days egg laying and 28 days incubation) was 40% for all 3 yr combined. Females laid just one clutch (usually of 4 eggs) each season, and mean clutch size was significantly smaller in 1979 than in 1977 and 1978. Estimated fledging success ranged from 0.40 in 1977 to 0.17 in 1978 and was consistently greater for females that nested early each season. Mean annual adult survival was estimated at 85% based on resightings of color-marked individuals. Limited data for subadult survival precluded complete demographic analysis. Nevertheless, given the estimates of productivity and adult survival pooled for 3 yr, survival of subadults from fledging until first breeding as 3-year-olds needed to be only 58% to maintain the stable population size observed through 1983. Received 10 June 1985, accepted 7 April 1986. THE population ecology of shorebirds (Charadrii) is not well known, probably because many species are wary, breed in remote areas, or both. Most thoroughly studied are species that nest at temperate latitudes such as the Eurasian Oystercatcher (Haematopus ostralegus; GossCustard et al. 1982, Safriel et al. 1984), Common Ringed Plover (Charadrius hiaticula; Laven 1940, Bub 1962, Pienkowski 1984a), and Common Redshank (Tringa totanus; Grosskopf 1959, 1964; Yates 1982). Many aspects of breeding biology are known for other shorebirds, especially in Europe and Scandinavia (see Cramp and Simmons 1982, Evans and Pienkowski 1984). But even among calidridine sandpipers (Scolopacidae), a subfamily with diverse social adaptations and mating systems (Pitelka et al. 1974, Myers 1981), detailed demographic parameters have been reported only for the Dunlin (Calidris alpina; Soikkeli 1967, 1970a, b) and Temminck's Stint (C. temminckii; Hilden 1978). Tringine sandpipers exhibit a wider range of body sizes and tend to breed at lower latitudes than do calidridines (Johnsgard 1981). Hence, they should be more accessible for study, and also more accessible for comparative demographic analyses. Long-term reproductive performance and population dynamics, however, are known for only a few smaller species such as the Spotted Sandpiper (Actitis macularia; Oring et al. 1983), Common Sandpiper (A. hypoleucos; Holland et al. 1982), and Common Redshank (Yates 1982). Larger species tend to be better studied during the nonbreeding season, and survival estimates based on annual returns to wintering grounds exist for Bar-tailed Godwits (Limosa lapponica) and Eurasian Curlews (Numenius arquata) (Evans and Pienkowski 1984). We studied breeding density, clutch size, nesting mortality, reproductive success, and adult survival in a population of Long-billed Curlews (Numenius americanus). These demographic data are integrated by life-table analyses, and the longer-term reproductive performance of the population is evaluated. STUDY AREA AND METHODS Study area. -The study area was an upland strip of shortgrass rangeland (-21,600 ha) in western Idaho (Redmond and Jenni 1982). We concentrated on a portion of the area (1,600 ha) that supported high breeding densities of Long-billed Curlews. This smaller plot was grazed intensively by large bands of sheep from late March through early May each year; other portions of the study area were grazed by cattle from November to June. Methods.-The nesting cycle was divided into prelaying, laying, incubation, and prefledging periods. A standard clutch of 4 eggs was laid in 4-7 days, and incubation began after the last egg was laid. Time from laying to hatching of the last egg was considered the incubation period; it ranged from 28 to 30 days (x = 28.4 days). 755 The Auk 103: 755-767. October 1986 This content downloaded from 157.55.39.185 on Thu, 26 May 2016 04:49:02 UTC All use subject to http://about.jstor.org/terms 756 REDMOND AND JENNI [Auk, Vol. 103 Population densities were estimated each year by a modified Finnish line-transect method (Redmond et al. 1981), and nests were located during egg laying or incubation according to methods described by Redmond (1986). When found, each nest was marked with a numbered wooden stake (2.5 x 5 x 40 cm) placed 10 m upslope from the nest cup. To deter mammalian predators from following our scent trails, paradichlorobenzene (PDB) crystals were sprinkled at a 1-m radius around each nest cup. On subsequent visits, a nest was always approached directly from the marking stake; when departing, a line of PDB crystals was spread across this path. Because the crystals were small and very volatile, they evaporated quickly and probably had only a short-term effect. Whereas the efficacy of this method for discouraging mammalian predators has never been tested, Lehner et al. (1976) showed that similar chemicals deterred coyotes (Canis latrans) and dogs (Canis familiaris) from food rewards. Similarly, Knight (1983) found PDB and napthalene to be useful in repelling skunks from specific areas. Nests found during incubation usually were checked every 2-5 days until the eggs first starred or pipped, and then every day until hatching was completed. Nests located during egg laying were not checked for the first 2-3 weeks of incubation. Clutch size was estimated by the maximum number of eggs found in a given nest. The diversity of potential predators on and around the study area made it difficult to interpret every act of predation and to identify responsible species. Mammalian carnivores that hunted regularly over portions of the study area included coyotes, feral dogs, feral cats (Felis domesticus), badgers (Taxidea taxus), and long-tailed weasels (Mustela frenata). Red foxes (Vulpes fulva), striped skunks (Mephitis mephitis), and raccoons (Procyon lotor) occurred on adjacent agricultural lands but were never seen hunting in upland hab-