Tuesday, December 29, 2015

Mountain Bluebirds, Mountain Bluebirds, Mountain Bluebirds.

It is clear that 2015 has been a tremendous year for Mountain Bluebirds in Nova Scotia. Many of our birders were able to add this western open-habitat thrush to their provincial list. These visiting rarities have been long-staying and have for the most part stuck to small areas making them easy to find.


2015 Timeline
Important observations of Mountain Bluebirds this year are listed below in chronological order:

  • Nov 15 - Simon-Paul d'Entremont photographed two bluebirds at Mavillette, Digby County. They were assumed to be Eastern Bluebirds at the time.
  • Nov 22 - David Bell and Dominic Cormier discover a hatch-year (HY) female Mountain Bluebird at Freeport, Digby County. See the eBird Checklist for photos.
  • Nov 22 - David Bell and Dominic Cormier find a HY male Mountain Bluebird at Mavillette, Digby County. See my eBird Checklist for photos from that day.
  • Nov 28 - Richard Hatch saw three bluebirds at Mavillette, Digby County, that he identified as two Mountains and one Eastern. No photos were taken that day and multiple birds were not observed again at Mavillette until Dec 26, see this item below.
  • Dec 2 - Cal Kimola Brown found a HY male Mountain Bluebird at Fish Plant Rd, Cape Sable Island, Shelburne County. The bird at this location was never resighted.
  • Dec 6 - Alix d'Entremont got two HY male Mountain Bluebirds (Fig. 1) at Church Hill Rd, Cape Sable Island, Shelburne County (only 0.5 km away from the Dec 2 sighting). One is likely the same that was photographed nearby on Dec 2 by Cal Kimola Brown. See my eBird Checklist for photos.
  • Dec 26 - Simon-Paul d'Entremont photographed two Mountain Bluebirds at Mavillette, Digby County. One is a HY male, and the other, a HY female.
A few questions arrise from the list of observations above.

What explains the lack sightings of multiple birds at Mavillette after Nov 28 and before Dec 26? The Mountain Bluebird at Mavillette was consitenty found at the Cape View Motel and Restaurant, but would sometimes dissapear to the south-east in the large expanse of coastal alders. Was this where the others were spending time?

Were the three bluebirds seen on Nov 28 comprised of the one HY male Mountain Bluebird and one Eastern Bluebird photographed on Nov 15 in addition to the HY female Mountain Bluebird from Freeport (Fig. 2)? Freeport is only 25 km from Mavillette, so that seems very possible also given that the age and sex of the bird is the same. In order to survive, vagrant birds will linger at good locations where they can find enough food. Mavillette, with its open landscape, appears to be an appropriate place for these bluebirds.

Figure 1. Two hatch-year male Mountain Bluebirds at Cape Sable Island, Dec 6, 2015. Photo by Alix d'Entremont.

Figure 2. Hatch-year females at Mavillette (Dec 26, 2015) and Freeport (Nov 22, 2015) that might be the same individual. Photos by Simon-Paul d'Entremont and David Bell.

There is precedence in Nova Scotia of different bluebird species in one location. On Jan 18, 1999, a Mountain Bluebird (present since Jan 16) in Centreville, CSI, was joined by an Eastern Bluebird. Both birds remained until at least Feb 7, 1999.


Historical Sightings in NS

I've combined all issues of NS Birds (previously named the Nova Scotia Bird Society Newsletter and later Nova Scotia Birds) into a 1.6 Gigabyte PDF complete with searchable text. This allows me to search by species name and find all occurances quickly.

  • Oct 25, 1989 - possible female at Hartlen Point, HRM.
  • Jan 27 - Feb 10, 1992 - our first fully confirmed, a HY male in Brooklyn, Queens County.
  • Jan 10, 1995 - female at Sable Island, HRM.
  • Jan 3, 1999 - immature at Port Morien, CBRM.
  • Jan 16, 1999 - female at Cape Sable Island, Shelburne County.
  • Nov 14-15, 2002 - female at Cape Sable Island, Shelburne County.
  • Dec 22-24, 2002 - one at Little River Harbour, Yarmouth County.
  • Jan 15-17, 2003 - one at Cape Sable Island, Shelburne County. *same as the Nov 2002 bird?*
  • mid-April, 2005 -  one at Long Island, Digby County. (7th)
  • May 23, 2007 - one in Upper East Green Harbour, Shelburne County.
  • May 10, 2009 - one in Dartmouth, HRM.
  • Dec 31, 2011 - one in Glace Bay, CBRM.

The above results in a total of 12 reports. There is a high probability that the Jan 2003 sighting was the same bird that was seen in Nov 2002. We are now left with 11 historical occurances of Mountain Bluebird in Nova Scotia. There have been at least 4 during 2015 (assuming the Freeport and Mavillette HY females are one in the same), the conservative total becomes 15. Twelve records have been during fall/winter and the remaining 3 in spring.


Migration and Vagrancy

Mountain Bluebirds are the most migratory of the bluebirds. They breed from east-central Alaska in the north to extreme west Texas in the south. They winter as far south as central Mexico and north to north-central Oregon. Depending on the severity of winter, they concentrate in the nothern of southern potion of the winter range. Autumn migration begins in August and extends into November. (Power & Lombardo, 1996)

The unprecedented number of Mountain Bluebirds in Nova Scotia during late fall and winter 2015 are mirrored by multiple sightings in other parts of eastern North America. Below are the number of Mountain Bluebirds reported to eBird in other eastern provinces and states.

  • Ontario - 2
  • Quebec - 1
  • New Brunswick - 1
  • Massachussetts - 1
  • Florida - 1

Figure 3 compares the eBird reports from fall migration 2014 to those of 2015. These maps allow us to visualize a phenomenon of vagrant Mountain Bluebirds that was not confined to NS. It is fair to say that a specific weather pattern at a particular latitude, altitude and time played a role in the arrival of the Mountain Bluebirds to eastern North America. During August and early September, we get airflow from the southwest. October through December is characterized by zonal airflow across North American from west to east, directly towards our province. This wind pattern contributes to the yearly arrival of birds from the west. (McLaren, 2012)

Another cause of vagrancy is misorientation, but the effect would be more consistent from year to year. A quick look through eBird shows that significant numbers of Mountain Bluebirds in the east, similar to the 2015 event, don't occur on a regular basis. The last time that we saw large numbers was during fall/winter 2011/2012.

Figure 3. Late fall/winter Mountain Bluebird eBird reports from 2014/2015 (left) vs late fall/winter 2015. From eBird.org.

Fall and winter 2015 were characterized by many other notable western vagrants to our province; these include Hermit Warbler, many Western Kingbirds, Bullock's Oriole, two American White Pelicans, an apparent "western" Marsh Wren and Western Flycatcher (Pacific-slope or Cordilleran).

One Mountain Bluebird in Nova Scotia is thrilling enough, but two separate locations with two individuals is amazing. Nova Scotia keeps providing evidence that it is truly a great place for vagrant birds. Its location (halfway between the north and south poles) and geography (surrounded by water and comprised of many headlands and islands) are great for producing exciting birding. (McLaren, 2012)


References

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

Power, Harry W. and Michael P. Lombardo. 1996. Mountain Bluebird (Sialia currucoides), 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/222
doi:10.2173/bna.222

6 comments:

  1. What an excellent job you have done, Alix, in documenting and examining the Mountain Bluebird occurances in Nova Scotia. Thank you so much!

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    1. You are welcome Joan. My pleasure.

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  2. Well done Alix! Love how you pull the information together.

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    1. Thanks Kim. Good to see it all in one place.

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  3. Great reporting Alix. Thanks. On the Putnam County NY CBC on January 2nd we didn't have the exotic Mountain Bluebirds but we did have unusually hundreds of eastern bluebirds in small pockets everywhere which certainly brightened the grey day.

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    1. That must have been quite a sight, Jane!

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