Mountain Bluebirds and Other Western Rarities

Figure 1. Mountain Bluebird at Mavillette, Digby, November 22, 2015. Photo by Alix d'Entremont.

On November 22, 2015, David Bell and Dominic Cormier found two Mountain Bluebirds, one at Freeport and another (Fig. 1) in Mavillette, both in Digby County. Paul Gould and I had just found a Yellow-breasted Chat in the multiflora brambles near Prospect St in Yarmouth when I received the good news about the Mavillette bird via text. We said our goodbyes to the chat and drove up Highway 101 towards my next lifer. Just north of Salmon River we noticed an interesting bird on the wires. We stopped to investigate and found that it was a Western Kingbird (Fig. 2).

Figure 2. Western Kingbird at Salmon River, Digby, November 22, 2015. Photo by Alix d'Entremont.

David and Dominic were still in Mavillette keeping an eye on the bluebird when we arrived. We quickly shook hands and thanked them as they had to leave to do maintenance on more radio bird tracking systems. The Mountain Bluebird was my 294th bird for the province.

The Mountain Bluebird breeds in western North America and is migratory in most of its range. It is a rare but regular vagrant to the East. There had previously been at least 11 reports of this western thrush in Nova Scotia, most during fall and winter. The last sighting was on 10 May 2009 in Dartmouth. (Mclaren, 2012)

Identification Tips

Lets begin by looking at structure to identify this bird to species. Compared to Western Bluebirds and Eastern Bluebirds, Mountain Bluebirds are longer-winged, longer-legged and thinner-billed (Alderfer, 2014). Figure 3 is very useful to compare structure between the Mountain Bluebird and Eastern Bluebird as both birds are in a similar position.

Figure 3. Mountain Bluebird (L) and Eastern Bluebird (R) at Mavillette November 15, 2015. Photos by Simon-Paul d'Entremont.

Mountain Bluebirds only have one moult per year, the pre-basic moult completed on the summering grounds. Therefore, there is no extreme difference in plumage between seasons. An adult male would be almost entirely sky-blue - clearly not matching our bird. A hatch-year male would be similar, but duller blueish to mixed brown and blue. Hatch-year males show strong moult limits in the greater secondary coverts - the inner ones having bright blue centres. The first pre-basic moult includes 1-8 inner greater coverts. A single bright blue replaced inner greater covert is visible in Figure 4. This replaced feather creates strong contrast with the remaining retained greater coverts. (Pyle, 1997)

Figure 4. Mountain Bluebird at Mavillette, Digby, November 22, 2015. Photo by David Bell.

Adult females are dull bluish gray and hatch-year females are dull brownish to grayish. The amount of blue on the bird combined with the presence of a strong moult limit in the greater coverts make it a hatch-year male. Some photos show more pure blue on the upperparts than others (Fig. 5).

Figure 5. Mountain Bluebird at Mavillette, Digby, November 23, 2015. Photo by Ellis d'Entremont.

Multiple Recent Western Vagrants

 Five western rarities were in s.w. Nova Scotia on November 22, 2015:

-Mountain Bluebird at Freeport, Digby
-Mountain Bluebird at Mavillette, Digby
-Western Kingbird at East Ferry, Digby
-Western Kingbird at Salmon River, Digby
-Western Kingbird at Louis Head, Shelburne

One could hypothesise that the weather system that brought hundreds of Franklin's Gulls to the eastern US mid-November contributed to the recent arrival of western birds to Nova Scotia. The track of the mid-November storm seemed favourable to bring some exciting birds to the Maritimes.

The Mountain Bluebird at Mavillette was actually present since mid-November. Simon-Paul d'Entremont had photographed two bluebirds at Mavillette on November 15 that were, at the time, passed off as Eastern Bluebirds. Once the November 22 bird was identified as a Mountain Bluebird, Simon and I reviewed his earlier images and were surprised that the rare bluebird was in fact present on November 15. One of the Simon's bluebirds was a Mountain Bluebird and the other was an Eastern Bluebird.

The Western Kingbird at Louis Head, Shelburne, was originally reported November 15. A Franklin's Gull was sighted briefly at Hall's Harbour, Kings, on November 19. The number of western vagrants concentrated in such a brief period provide evidence supporting a weather-driven arrival.

References

Alderfer, J., J.L. Dunn. 2014. (Ed). Complete Birds of North America, 2nd Edition. National Geographic Society. Washington DC, USA.

McLaren, I.A. 2012. All the Birds of Nova Scotia: status & critical identification. Gaspereau Press Ltd, Kentville, N.S., Canada

Pyle, P., S.N.G. Howell, R.P. Yunick, and D.F. Desante. 1997. Identification guide to North American Birds, Part 1, Columbidae to Ploceidae. Slate Creek Press, Bolinas, California.