The eBird bar charts give us "frequency: the percentage of checklists reporting that species within a specified date range" - so it gives you an idea of how likely are you to encounter that species during that time frame in appropriate habitat.
These data
don't really tell us about the actual abundance of the species - the
size of their populations (because of the variety of counting methods
and observer effort used to get these eBird data, and other things) ... but ...
intuitively, if there are changes in frequency for really common birds -
that must say something.
So, I have compared a species' frequency from December 2021 to the frequency from 2016 - in a very imprecise way that would not stand up to statistical analysis. I have summed the year's frequency for 2016 and for 2021 and compared them by subtracting the 2016 number from the 2021 number. Here are the results for the top and bottom 30 species - the 30 species that show the greatest increase or decrease in frequency since 2016.
eBird Regional District of East Kootenay Frequency Difference
| English Name | BC_Game | Abundance | Diff_2021 | |||
| American Crow | vc | 3.912559532 | ||||
| Common Raven | g | vc | 3.267595681 | |||
| Canada Goose | g | vc | 2.520634189 | |||
| Northern Flicker | vc | 2.459357979 | ||||
| Bald Eagle | c | 2.431250047 | ||||
| Mallard | g | vc | 2.289990853 | |||
| Red-breasted Nuthatch | vc | 2.125886915 | ||||
| Dark-eyed Junco | vc | 1.596265554 | ||||
| American Robin | vc | 1.506643623 | ||||
| Rock Pigeon | g | vc | 1.454782405 | |||
| Blue Jay | sc | 1.313311740 | ||||
| Eurasian Collared-Dove | g | sc | 1.255200966 | |||
| Black-billed Magpie | c | 1.118253242 | ||||
| Bufflehead | g | c | 1.115452534 | |||
| American Wigeon | g | c | 1.098214353 | |||
| American Coot | g | c | 1.089445026 | |||
| Turkey Vulture | sc | 0.987196201 | ||||
| Pine Siskin | vc | 0.920770842 | ||||
| European Starling | vc | 0.916598597 | ||||
| Townsend's Solitaire | c | 0.910150795 | ||||
| Red-tailed Hawk | c | 0.876833943 | ||||
| Ring-necked Duck | g | c | 0.863093321 | |||
| Trumpeter Swan | sr | 0.862401577 | ||||
| Tree Swallow | vc | 0.835159263 | ||||
| Osprey | c | 0.786232455 | ||||
| Green-winged Teal | g | c | 0.763347806 | |||
| Vesper Sparrow | c | 0.760730881 | ||||
| Western Bluebird | c | 0.744897794 | ||||
| Eastern Kingbird | c | 0.731731785 | ||||
| Killdeer | c | 0.730740303 | ||||
| English Name | BC_Game | Abundance | Diff_2021 | |||
| Ruffed Grouse | g | c | -0.068174952 | |||
| Barrow's Goldeneye | sc | -0.074931879 | ||||
| Calliope Hummingbird | sc | -0.088113133 | ||||
| White-crowned Sparrow | sc | -0.088878485 | ||||
| Black-headed Grosbeak | sr | -0.098174169 | ||||
| Brown-headed Cowbird | c | -0.098403200 | ||||
| Common Grackle | sc | -0.100154859 | ||||
| Northern Shrike | sc | -0.116332190 | ||||
| Black Tern | unc | -0.122280235 | ||||
| White-throated Sparrow | sr | -0.140874202 | ||||
| Northern Waterthrush | c | -0.155879991 | ||||
| MacGillivray's Warbler | c | -0.172119636 | ||||
| House Finch | vc | -0.181452069 | ||||
| Clark's Nutcracker | vc | -0.199776593 | ||||
| Warbling Vireo | c | -0.228123752 | ||||
| Great Blue Heron | sc | -0.229904927 | ||||
| Townsend's Warbler | c | -0.245286146 | ||||
| Hairy Woodpecker | vc | -0.249200275 | ||||
| Song Sparrow | vc | -0.265412316 | ||||
| American Dipper | c | -0.286035808 | ||||
| Vaux's Swift | c | -0.316657000 | ||||
| Rufous Hummingbird | c | -0.454750968 | ||||
| Bohemian Waxwing | c | -0.540717624 | ||||
| Common Redpoll | c | -0.571101261 | ||||
| Pine Grosbeak | c | -0.779422544 | ||||
| Black-capped Chickadee | vc | -0.803501285 | ||||
| Evening Grosbeak | c | -0.962873544 | ||||
| White-breasted Nuthatch | sc | -1.054325951 | ||||
| Downy Woodpecker | vc | -1.114156219 | ||||
| Steller's Jay | c | -1.154665009 |
So, now you are more likely to see American Crow, Common Raven, Canada Goose, Northern Flicker, and Bald Eagle, etc. when you go out birding; and less likely to see Steller's Jay, Downy Woodpecker, White-breasted Nuthatch, Evening Grosbeak, Black-capped Chickadee, etc. than you would have five years ago.
I think decreases in the very common (vc) species indicates there are some population problems with them: they used to be commonly seen but are seen less often now, probably because there are fewer of them around, not because of some change in their behaviour or birders' behaviour. And fewer of them around either because their populations are smaller or because there is less habitat available for them.
This is troublesome to think about for Downy Woodpecker and Black-capped Chickadee, especially. Why? They are easily identifyable and still fairly common but why would they be reported less unless there are just fewer of them to report? And Hairy Woodpecker and Song Sparrow? What's up with them? And Rufous Hummingbird - hmm.
Clark's Nutcrackers and Great Blue Heron we know are having trouble. Nutcrackers with food supply in higher elevations: less productive limber pine seed crop, limber seeds having higher energy rewards than lodgepole pine. And Herons having trouble with finding suitable nesting sites - and maybe more predation from a higher Bald Eagle population?
It's good to see Northern Flicker increase in frequency - they carve out lots of cavities for other birds to use as nests and help recycle dead trees. Eurasian Collared-Dove we know has just "recently" arrived in the area and their population is currently growing rapidly. They used to be rare but it didn't take long for them to become quite noticeable in human-settled areas.
The increasing frequency of seeing Bald Eagles: if their numbers are indeed growing, that is fine - we need "top of the food chain" species as part of the overall balance. Why would they be increasing? Maybe warmer springs lets them get going earlier laying eggs and that translates to better survival of young? Maybe they are taking advantage of having more Mallards around to eat?
So, yeah, the 2021 frequency data is cumulative and includes the same data as in the 2016 number. Both frequency numbers contain all the data in eBird up until that point in time. That adds some evening. This is not comparing 2016 and earlier to the time frame of 2017 - 2021.
You can see the eBird bar chart here: https://ebird.org/barchart?byr=1900&eyr=2020&bmo=1&emo=12&r=CA-BC-EK
And you can change the dates to see the differences for yourself, and you can download the numbers - scroll to bottom, "Download Histogram Data".
Yes, there are more eBirders now, but this is frequency data - so that is factored in. What is not factored in is skill of the eBirder at detection and many other things - that's why this discussion is not very rigorous scientifically but it does give one something to think about.
