Wednesday, February 6, 2013

Local Birds and Climate Change by Tom Pirro (reporting from Massachusetts)



Local Birds and Climate Change 

By Tom Pirro
(reporting from Massachusetts)




Many bird enthusiasts in central Massachusetts now enjoy both Red-bellied Woodpeckers and Carolina Wrens at their feeding stations. But, it wasn’t too many years ago when an area sighting of either of these handsome birds would have been news worthy. In the early years of their range expansion, their presence was first into the milder regions of the state toward New Bedford, Fall River and Cape Cod. Eventually they spread into Greater Boston, the North Shore and Southern Worcester County; and are now regulars in the hill towns of North Quabbin and Worcester County. 


Carolina Wren.  Photo: Tom Pirro
I regularly see Red-bellied Woodpeckers at my feeding station in Westminster and they’ve become widespread across North Central Massachusetts and is no longer restricted to lower elevations. The same holds true for the Carolina Wren, however its habitat is restricted to brushy thickets. 
Red-bellied Woodpecker.  Photo: Tom Pirro


Below is data from the two Massachusetts Breeding Bird Atlases, the first took place from 1974 to 1979 and the second from 2007 to 2011. The Massachusetts Audubon Society spear headed both campaigns, dividing the state into roughly 1000 “blocks” which were surveyed by hundreds of volunteer field observers. The frequency in which each of these species has increased is staggering.

Red-bellied Woodpecker

Breeding Bird Atlas 1 (1974-1979)
Breeding Bird Atlas 2 (2007-2011)
Blocks Present
4
783
Blocks Surveyed
969
1055
Percent
0.4%
74.2%
Carolina Wren

Breeding Bird Atlas 1 (1974-1979)
Breeding Bird Atlas 2 (2007-2011)



Blocks Present
66
751
Blocks Surveyed
969
1055
Percent
6.8%
71.2%



The Red-bellied Woodpecker and Carolina Wren are considered resident species and remain fairly close to their breeding territories throughout the year, with the exception of a post breeding dispersal. National Audubon’s annual Christmas Bird Count data shows a similar trend to the breeding atlas data, with a dramatic increase since 1970. It superficially appears their respective numbers maybe beginning to stabilize, but continued monitoring will track their future population in our region.




Evening Grosbeaks
In contrast to the recent arrival of the red-bellied Woodpecker and Carolina Wren has been the dramatic decline of wintering Evening Grosbeaks. It hasn’t been  too many years since roving flocks of this species would decimate sunflower seed stocked at feeding stations, to the point of nearly out competing Gray Squirrels! Over the past 15 years this species has become increasingly scarce in the North Quabbin and Worcester County regions, a former winter strong hold for this large and attractive finch. The Christmas Bird Data painfully supports this observation, in recent years both the Athol and Westminster CBC’s often miss this species on the count, unheard of a decade ago! 


Bicknell Thrush
In many cases, such as with the Red-billed Woodpecker, this may not be bad news as there appears to be plenty of suitable habitat (deciduous forest) to allow a northward expansion. Of concern are species with more northerly distribution which may get crowed off the continent. The Bicknell’s Thrush which inhabits elevations generally above 3000 feet in balsam fir has a range limited to the Northeastern US and Southeastern Canada.  (see below).  This species once bred on Mount Greylock in Western Massachusetts, but only one was detected during the most recent Breeding Bird Atlas and likely a late migrant. Of concern for this species is the threat of a warming climate that could essentially  “flood” the Bicknell’s Thrush from its elevated island breeding grounds. 
Bicknell’s Thrush range mapWikipedia

There are many reason for a species range expanding or contracting.  Global climate, which is  currently being “assisted” by humans, is certainly one of them.  According to Audubon, 60% of 305 regularly occurring winter species are shifting their respective ranges an average of 35 miles northward, while less than ½ that number appear to be averaging a more southern winter distribution. Certainly some species such as Red-bellied Woodpeckers and Carolina Wren may benefit (at least in our region) while others may not, such as Evening Grosbeaks. More concerning are species with limited ranges which may be driven from existence such as the Bicknell’s Thrush.

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