I’m in the East Bay for a while and I came across this article in Bay Nature that says:
“Acorn woodpeckers, for example, are uncommon to rare in most California coastal sites where only a single species of oak—typically coast live oak—grows, but are common inland where several oak species live together. (Acorn woodpeckers are rare in Oakland and Berkeley, but common in Orinda and Lafayette.) When only a single species of oak grows in an area, crop failures are apparently too frequent for the birds to survive” The Enduring Mystery of Oak Tree “Mast” Years - Bay Nature
And I thought “Inaturalist might provide evidence that might support this statement.” and sure enough iNat sightings of Acorn woodpeckers are rare in Berkely and Oakland, but common in Orinda, etc. . … but then I wondered if one could corelate the number of oak species observations with the observations of Acorn woodpeckers - that is overlay different oak species on a map of Acorn woodpeckers observations and see if iNat provides any evidence that the second part of the excerpt above is true. Essentially a map that would overlay different Oak species observations over Acorn woodpecker observations and distinguish between the types of oaks - More than one type = Acorn woodpeckers - Only one type = no (or few) Acorn woodpeckers.
I couldn’t figure out how to do it. Can it be done?
Thank you. I think I got that, but I’d like to be able to add another species of oak - or Oaks - Valley Oak, or Canyon Live Oak as well as Coast Live Oak, for example and be able to distinguish between the Oak types.
That works and it kinda confirms the statement. Below is a snip that shows Berkeley with Acorn woodpeckers and Oaks other than Coast Live Oak -which grow - or did grow throughout the region - (I took them out because they just cluttered up the map) and it seems to lend evidence that two species of Oaks are required to maintain an Acorn Woodpecker population… although I’m sure other factors come into play - like asphalt everywhere in the actual city.
Interesting, there are several outliers here; Tomales Bay by Point Reyes, Pacific Grove (or to some degree all of Monterey Bay), and Elkhorn Slough, for example. I double-checked each site for all oak species and it appears coast oaks are very much the dominant oak, with few other species. Makes me wonder if these are actually outliers suggesting other factors impacting Acorn Woodpecker abundance or the data are skewed due to increased observation numbers or observation emphasis on a particular taxonomic group (birds).
It looks like Tanoak fills the role of the second species to supplement Coast Live Oak around Tomales Bay.
But, for Monterey Bay and Elkhorn Slough the only species in significant numbers is Coast Live Oak. Perhaps Acorn Woodpeckers can tolerate these areas because acorn production is for some reason more reliable by those live oaks, or perhaps the woodpecker observations reflect populations that migrate elsewhere in lean years to find acorns on other (two-year) oak species.
Walt Koening’s Bay Nature article actually starts with his horrified discovery that two-thirds of Acorn Woodpeckers left the upper Carmel Valley in the acorn “bust year” of 1983. So I guess that changes the question to:
Among regions with only a single oak/tanoak species, why do Acorn Woodpeckers avoid some regions altogether while they’re wiling to inhabit others except in “bust years”?
Thanks to everyone who contributed to this thread. I learned a few things and I thought of a few other things to check out - Scrub Jays and oaks, various butterfly species and host plants, etc. - It just helps to illustrate the potential utility of iNat.