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La Crescenta, CASign In to follow
This is a young Baltimore Oriole, due to the bright orange breast, the black line through the eye, the fairly large bill, and large size. Baltimores are more apt to be confused with the closely related Bullock's Orioles (rare in Costa Rica during winter), which are very similar but have the orange brightest on the head rather than the breast, and a paler gray body. Young and female Orchard Orioles are much smaller and greener, with short pointed bills, and are more likely to be confused with a Hooded Oriole (absent from Costa Rica).
This is a Song Sparrow; note the reddish-brown color (grayer on a Lincoln's) and coarse brown streaks (crisper streaks contrasting with a buffy breast on Lincoln's). Lincoln's also has a relatively smaller, more slender bill.
This is a Nuttall's Woodpecker for a few reasons, namely: 1) Ladder-backed Woodpecker is a desert species that occurs in CA only in the southeast, overlapping with the Nuttall's in Los Angeles and Kern counties, and 2) the upper back is completely black, whereas the white stripes would extend to the nape in the Ladder-backed.
While you're technically correct (this is a gull and it is on the Pacific), Pacific Gull is actually a much larger species from Australia. (http://en.wikipedia.org/wiki/Pacific_Gul...) Here on the Pacific coast of North America, the typical dark-backed gull is the Western Gull.
At this distance, it's hard to be sure, but this looks to be either an Indian Cormorant (Phalacrocorax fuscicollis) or a Little Cormorant (P. niger). The only other cormorant in the area, Great Cormorant (P. carbo), is much larger and thicker-headed. With the pale underparts, this is likely a juvenile; adults are uniform blackish, save the coloring of the bare skin and feathers of the face.
The Bahama Mockingbird ID is incorrect: that species is confined to the northern Caribbean islands (Bahamas, Cuba, Jamaica, Turks & Caicos, with occasional vagrancies to Florida), and has distinctly streaked undersides and lacks the prominent white eye stripe seen in the Tropical Mockingbird here (found from southern Mexico to Brazil, and in the southern Caribbean in the Lesser Antilles, Trinidad & Tobago, and Aruba and its neighboring islands; a bird just showed up in Texas this week, a first North American record). That sentence was rather long, but I think the point needed to be made. Just trying to help!
This is actually a song sparrow. Lincoln's sparrows have finer streaks and a buffy wash over the chest that contrasts with a white belly, while song sparrows have thicker streaks that often converge into a central spot and all-white underparts.
This is either a Downy (Picoides pubescens) or Hairy (P. villosus) Woodpecker - their plumage is essentially identical (they're the only woodpeckers in North America with white backs), and the best way to tell them apart is by size, the Hairy being larger, with a longer bill, and more fond of bigger trees, while the Downy is smaller and common in gardens across the continent. It's hard to tell from this picture exactly which species this is, though.