Wilson's Warbler

Wilsonia pusilla
STANFORD LOCATIONS:

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.
  
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.
ESSAYS: Polygyny; Monogamy; Average Clutch Size; Variation in Clutch Sizes.
REFERENCES: Stewart et al., 1977.

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Except for Stanford Locations, the material in this species treatment is taken, with permission, from The Birder's Handbook (Paul Ehrlich, David Dobkin, & Darryl Wheye, Simon & Schuster, NY. 1988).