Northern Parula (Parula americana) is a fairly common nesting species, common migrant and uncommon winter resident along Florida's west coast. During the winter they can be found foraging in almost any woody vegetation. During the nesting season they are found almost exclusively in association with forest vegetation where Spanish moss grows in profusion. Spanish "moss" isn't really a moss but an epiphytic plant that grows on and from another host plant species.
The Florida Breeding Bird Atlas shows the range of this species during the nesting season in Florida. Note that Sarasota County is about at the southwestern limit of its nesting range.
I heard the first apparently territorial male Northern Parula of the year on March 10 2009. Since then I have heard them daily ever since. I have at least five territorial males that I hear regularly on my daily 16-mile bicycle rides through urban areas of Sarasota County. Just today for instance, June 19, 2009, at 2:00 p.m. with the temperature at 92 degrees I heard the same five males singing. Two of them are on opposite sides of Honore Avenue where they are consistently and persistently singing throughout the day. It doesn't matter how hot it is or the angle of the sun, these birds keep singing and defending their territories.
In my native Wisconsin I remember first seeing Northern Parula on migration about May 10 and during the nesting season you could hear them singing until about July 10 or so. Hearing one sing after 11:00 a.m. would be a rarity at the end of the nesting season. Once their brood was out of the nest the singing ceased. However here in west Florida they seem to not want to give up. Given that they started singing in early March and given the short incubation and nestling period of wood warblers, the birds now have to be on their second broods. The Florida Breeding Bird Atlas mentions that they stay on territory until early August. I wonder if they have three broods?
I'll have to keep my ears piqued to determine how long I keep hearing these warblers singing. Don't get me wrong - I love the sound of singing warblers. I'm just baffled that they are still at it and in the middle of the day when most "normal" birds would have given up and conserved some energy.
The photo is from a US Forest Service link. No attribution given on the site so I assume its in the public domain.