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How can you correct this for "reporting errors?"  Have you checked how many
checklists were submitted each year?

On Sun, Sep 15, 2019 at 8:55 AM Ian Worley <[log in to unmask]> wrote:

> 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
>
>
> -----------------------------------------------------------------------------------------------------------
> 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
>


-- 
Best regards,

Leslie

Leslie Nulty
P.O. Box 1121
Jericho Center, VT 05465
home office: 802-899-4582
cell: 802-324-1496