Whilst birding the ‘patch’ in the spring a number of Upcher’s Warblers have been seen with the highest daily count five birds. They are mainly seen in the scrub and bushes near to the spray fields and percolation pond with the below photos taken at the edge of the spray fields. The main identification points to separate Upcher’s Warbler and Eastern Olivceous Warbler are that Upcher’s Warbler is generally bigger and has a more stocky appearance although this can be difficult to judge on a lone bird if unfamiliar with them. Wings, legs, tail and bill are all longer on Upcher’s Warbler than on Eastern Olivaceous Warbler with the legs and bill being thicker on Upcher’s Warbler. The tail on Upcher’s Warbler is long and ‘full’ and darkens towards the tip, which is not the case in Eastern Olivaceous Warbler. This darkening of the tail can be seen clearly in the below photographs. The tail is also moved in a rather lazy swinging motion often sideways and also upwards and is also fanned, which is not often if ever shown by Eastern Olivaceous Warbler. The exaggerated tail movements of Upcher’s Warbler are often the first thing that draws attention to the species, especially if they are deep in cover.
The wing is fairly dark and contrasts with the mantle and also has quite a long primary projection and the wing has a pale whitish secondary panel in Upcher’s Warbler, with Eastern Olivaceous Warbler having a paler less contrasting wing with shorter primary projection and a pale buffish secondary panel which is much less obvious and more difficult to see than the panel in Upcher’s Warbler. Another quite obvious difference is the spacing on the tertial feathers, with the tip of the middle terital closer to the outermost tertial than it is to the innermost one on Upcher’s Warbler and these being evenly spaced on Eastern Olivaceous Warbler.
The general plumage of Upcher’s Warbler is quite greyish, rather than the brownish and yellowish tone of Eastern Olivaceous Warbler and the lores appear quite bare on Upcher’s Warbler. Lastly the bill is relatively stout looking and has a pale pinkish base on Upcher’s Warbler, and is less stout with a yellowish base on Eastern Olivaceous Warbler.