Early Philadelphia Vireo spring migration?

Last week, Roselvy and I saw a Philadelphia Vireo in a mixed flock of insectivores working the slope of an oak forest on Montaña de Isopo, about 20 km south of Tegucigalpa, the capital of Honduras. Philadelphia Vireo winters in southern Central America, and this past winter we saw this species occasionally in our area here in Honduras. I took the photo above on January 8, 2012 in a forest near Santa Ana where we live.  

Today, however, I heard a Philadelphia Vireo singing from the neighbors' yard across the road from our house. That bird I assume is a migrant, because I never heard or seen one there before, and also because it was singing. According to the BNA account, Philadelphia Vireos do not sing in fall or winter, but they sing during spring migration (Moskoff & Robinson 2011), a trait they share with the Red-eyed Vireo (Skutch 1960). Many warblers also sing during spring migration, though usually closer to the breeding grounds (Dunn & Garrett 1997). 

Three days ago, two Philadelphia Vireos were also seen on the campus of the UNAH (Universidad Nacional Autónoma Honduras) in Tegucigalpa, Honduras (ebird.org), where they presumably did not winter. 

Normally, Philadelphia Vireo departs from the wintering grounds mid- to late April, and the extreme dates for Veracruz, Mexico - where it is a transient - are 16 Apr－24 May (Winkler et al. 1992, cited in Moskoff & Robinson 2011). Late April to mid-May, the birds pass through the southern US states and late May is when they pass through the northeast.

I wonder if observers in Mexico and the US will note early Philly Vireo migration this spring.

Cited literature

Dunn, Jon and Kimball Garrett. 1997. A Field Guide to Warblers of North America. Peterson Field Guide Series 49. Houghton Mifflin Company, New York.

Moskoff, William and Scott K. Robinson. 2011. Philadelphia Vireo (Vireo philadelphicus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/214

Skutch, A.F. 1960. Life Histories of Central American Birds II. Pacific Coast Avifauna 34. Cooper Ornithological Society. Berkeley, California.