Photographed the endangered (in Canada) Prothonotary Warbler along the Tulip Tree Trail at Rondeau Provincial Park.

The Prothonotary warbler is the only cavity-nesting warbler in North America and typically selects a small hole, low in the trunk of a decaying tree, as the site in which to build its moss-lined nest. Its breeding habitat is protected at Rondeau Provincial Park and in the Long Point National Wildlife Area. Man-made nest boxes have been established as part of a recovery plan and some can be found at Rondeau. Source for the above info is from the Royal Ontario Museum website.

Bird Studies Canada website has this to say: "The Prothonotary warbler breeds throughout the eastern U.S, and north to extreme southwestern Ontario. It is most abundant in the southeastern U.S. and up the Mississippi River. Being at the fringe of its range in southwestern Ontario, the Prothonotary Warbler is almost entirely restricted
to a few areas on and adjacent to the Lake Erie shoreline (Holiday Beach, Pelee Island, Point Pelee, Wheatley, Rondeau, Long Point, and Point Abino). It also regularly occurs in Hamilton, and occasionally nests at Pinery Provincial Park on Lake Huron. The "core" populations in Canada reside in Rondeau Provincial Park and the Long Point region.

In spring, the Prothonotary begins to return to southern Ontario in the first week of May. Males generally precede females by about 2 weeks, and older birds of both age groups precede younger ones. The entire adult population is usually back on its nesting grounds by the first week of June,
but some younger females dilly-dally and may not arrive until the end of June. By the time the females are back, the males have already established their territories and begun to select potential nest sites for the females to inspect. Since it cannot excavate its own, it happily uses naturally formed hollows and those excavated in previous years by chickadees and Downy
Woodpeckers. Cavities that are fairly low (usually 1-3 metres) are greatly favoured, especially if they are over open pools of water. Other than that, Prothonotaries are not terribly fussy about the cavity." --- BSC website.