Wilson's Warbler Wilsonia pusilla Wilson       Field Guide IDs: NG-384; G-292; PE-242; PW-pl 51; AE-pl 358; AW-pl 409; AM(III)-180 Nest Location Nest Type Eggs & Mating System Dev. & Parental Care Primary & 2ndary Diet.. Foraging Strategy F I: 10-13 DAYS ALTRICIAL VINE .........TANGLE 0 - 3 feet F 4-6 (2-7) MONOG (POLYGYN) F: 8-11 DAYS MF HOVER & .........GLEAN HAWKS BARK.. ....GLEAN BREEDING: Thickets and brush in well-watered locations (esp willow and alder bogs), riparian woodland. 1 brood. DISPLAYS: ? NEST: Variably placed: high-elevation nests are smaller and built on ground; coastal nests larger and above ground. Bulky, esp for such a small bird; of dead leaves, grass, moss, lined with fine grass, occ hair. Built in 5 days. EGGS: White to creamy, marked with browns, variable, often wreathed. 0.6" (16 mm). DIET: Also occ berries. CONSERVATION: Winters s to w Panama. Uncommon cowbird host. NOTES: Breeds over a wide range of elevations: coastal populations have smaller clutches, lower nesting success, and are monogamous; high-elevation populations have larger clutches, higher nesting success, and polygyny occurs regularly. Females brood. Much more common in w than in e. STANFORD. NOTES: Uncommon to fairly common migrant and summer resident in woodland and scrub near the Dish, with a few pairs probably nesting there. Uncommon migrant elsewhere on campus. ESSAYS: Polygyny; Monogamy; Average Clutch Size; Variation in Clutch Sizes. REFERENCES: Stewart et al., 1977.