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Hello all!

Near the end of August there were a number of birders wondering about 
swallow numbers in Vermont.  It seem as if there were not nearly as many 
as in previous years.

To see if this was really the case, I thought I'd use eBird data to 
compare 2019 August data with the corresponding data for the preceding 
five years (2014-2018).  I chose the eBird "abundance", taking the data 
from the eBird graphs.

"Abundance" is the average number of birds reported on all checklists 
within a specified date range and region (for us that means August and 
Vermont).  It is a rather esoteric number, good for the comparisons we 
are interested in here, though rather hard to relate the numbers to any 
one specific birding outing.  The principal caution in this analysis is 
that the fewer the number of checklists the less meaningful the 
"abundance" number.  This is one reason for looking at the whole state's 
numbers.

Basically, a higher "abundance" number mean more birds in the 
geographical area of interest.  The higher the number, expect to see the 
species more often and/or in larger numbers.

Details are below, but first the grand results ------

----- For all five species of swallows combined, August 2019 had fewer 
swallows than any of the five preceding Augusts.  The abundance of 
swallows in August 2019 was only 67% of the average August abundance of 
swallows over those five preceding years.

----- Species by species, the abundance of birds in August 2019 was 
sometimes greater and sometimes less than during one or more of the 
previous five years.

----- Otherwise, the numbers from year to year show no abundance trends, 
either for the individual species or for all swallows as a whole (albeit 
this look is only six years).  For example, the abundance numbers for 
all species of swallows for the whole state from 2014 to 2019 are:

2014    9.64
2015    11.01
2016    8.55
2017    11.83
2018    7.81
2019    6.55

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Here are comparisons for each of the species from the most abundant 
specie to the least, as per 2019.

Barn Swallow [2019 August abundance 0.91]
--- 2019 fewer than two years, greater than three years
--- 90% of previous five year average
--- Most abundant in 2014; least abundant in 2017

Tree Swallow [2019 August abundance 0.56]
--- 2019 fewer than all five previous years
--- 42% of previous five year average
--- Most abundant in 2017; least abundant in 2019

Bank Swallow [2019 August abundance 0.03]
--- 2019 fewer than one year; greater than four years
--- 53% of previous five year average (data skewed by very large 
abundance in 2018)
--- Most abundant in 2018; least abundant in 2014

Northern Rough-winged Swallow [2019 August abundance 0.013]
--- 2019 fewer than three years, greater than two years
--- 108% of previous five year average
--- Most abundant in 2018; least abundant in 2016 and 2017

Cliff Swallow [2019 August abundance 0.01]
--- 2019 fewer than all five previous years
--- 30% of previous five year average
--- Most abundant in 2017; least abundant in 2019

All species combined [2019 August abundance 6.17]
--- 2019 fewer than all five previous years
--- 63% of previous five year average
--- Most abundant in 2017; least abundant in 2019

-------------------------------------------------------------------------------------
I thought I'd take a peek at county-level data, wondering if 2019 county 
August abundance values different from the state as a whole values.  
Here are three county comparisons.  As suspected, the counties vary in 
terms of the number birds per species; to get the full picture for the 
distribution and abundance of the swallow species one really needs to 
look at all the counties.

Barn Swallows
--- Vermont  0.91
--- Chittenden County  0.87
--- Windham County  0.60
--- Washington County  0.03


Tree Swallows
--- Vermont  0.56
--- Chittenden County  0.35
--- Windham County  0.34
--- Washington County  0.10


Northern Rough-winged Swallows
--- Vermont  0.013
--- Chittenden County  0.12
--- Windham County  0.00
--- Washington County  0.00


Bank Swallows
--- Vermont  0.03
--- Windham County  0.05
--- Chittenden County  0.01
--- Washington County  0.0


Cliff Swallows
--- Vermont  0.01
--- Chittenden County  0.02
--- Windham County  0.00
--- Washington County  0.00

Best to all ...............

Ian