eBirding and County Birding the Tennessee Warbler


Ethan Monk
 

Recently the Tennessee Warbler in Contra Costa/Alameda counties in Creekside Park (El Cerrito/Albany) has been a source of confusion for some birders who are unsure where the county line falls. So in response to those who asked me to write a post clarifying, here it is, and if I am wrong please correct me!

On the internet, there are generally two different maps used to illustrate the CC/ALA Co. line at this location. One commonly used map shows the county line bisecting El Cerrito Creek clean down the middle from the bayshore to Carlson Blvd. This is the line that has been traditionally used by birders. Yet, a considerable subset of maps, including the Caltrans Map, shows the county line deviating from the Creek as it passes West under Carlson Blvd., and following the concrete walking path through Creekside Park. In some places, this revised county line would put the boundary 30 or so feet North of the creek, and would jeopardize Contra Costa's single Mourning Warbler record.

I have done some research, and to my understanding, the CC/ALA line does truly follow the center of El Cerrito Crk from the bay through the park and to at least Carlson Blvd. The second version of the map that shows the county line deviating North of the creek along the concrete path appears to be a propagation of an error made somewhere in the past. While most parks are treated as one single parcel, Contra Costa treats its section of Creekside Park as four individual parcels: two North of the path, and two South of the path. The county line maps that show deviation from the creek follow the border between those two Northern parcels and the two Southern parcels, as if the Southern parcels are in Alameda, even though the two parcels South of the concrete path and North of the creek are mapped, assessed, etc. by Contra Costa County. And the two Southern parcels have their Southern boundaries in the middle of the creek reaffirming that yes, the county line runs down the middle of El Cerrito Creek.

If you wish to use the Caltrans map and consider the concrete path the county boundary for your personal listing convenience, feel free--it is not my list, but I would recommend not telling anyone.

Ethan Monk


Aaron Maizlish
 

No buddy, it’s much worse than you think.  Birders have been using that creek bed as the county line forever, since that makes the most sense.  But that creek bed alignment and the concrete path that you mentioned are modern inventions that are probably100 years newer than the county boundary.  So I’ve known for some time that most of the modern creekbed is firmly on the Contra Costa County side, and the reality is that the county boundary is a straight line.   But this truth has been too hard to bear.

The entire creekbed is really Contra Costa from the frontage road to about Yosemite Avenue, according to both the Contra Costa GIS and the Albany GIS.  There is a small parcel between the apartments and the realigned creekbed, probably created for the park, that is part of the city of Richmond (as is the shopping center) even though it's entirely the south of the creek.  East of the apartments, the footpath is on the Alameda side of the line, but only by a couple feet, the creek is CoCo on both sides.  At about Yosemite Ave and to the east, the county line is at about the middle of the creek.

Now I really didn’t want to lose Noah’s Mourning Warbler record for Alameda - do you?  Let’s just pretend the creek is still the line, because surveyors that’s what the original surveyors would have wanted.  To do otherwise would be to start splitting trees in half.   I can’t send the map to the group (attachments aren’t allow, by popular request, but contact me offline if you want a screen capture.




Aaron Maizlish
San Francisco






On Sep 11, 2021, at 5:48 PM, Ethan Monk <z.querula@...> wrote:

Recently the Tennessee Warbler in Contra Costa/Alameda counties in Creekside Park (El Cerrito/Albany) has been a source of confusion for some birders who are unsure where the county line falls. So in response to those who asked me to write a post clarifying, here it is, and if I am wrong please correct me!

On the internet, there are generally two different maps used to illustrate the CC/ALA Co. line at this location. One commonly used map shows the county line bisecting El Cerrito Creek clean down the middle from the bayshore to Carlson Blvd. This is the line that has been traditionally used by birders.  Yet, a considerable subset of maps, including the Caltrans Map, shows the county line deviating from the Creek as it passes West under Carlson Blvd., and following the concrete walking path through Creekside Park. In some places, this revised county line would put the boundary 30 or so feet North of the creek, and would jeopardize Contra Costa's single Mourning Warbler record.

I have done some research, and to my understanding, the CC/ALA line does truly follow the center of El Cerrito Crk from the bay through the park and to at least Carlson Blvd. The second version of the map that shows the county line deviating North of the creek along the concrete path appears to be a propagation of an error made somewhere in the past. While most parks are treated as one single parcel, Contra Costa treats its section of Creekside Park as four individual parcels: two North of the path, and two South of the path. The county line maps that show deviation from the creek follow the border between those two Northern parcels and the two Southern parcels, as if the Southern parcels are in Alameda, even though the two parcels South of the concrete path and North of the creek are mapped, assessed, etc. by Contra Costa County. And the two Southern parcels have their Southern boundaries in the middle of the creek reaffirming that yes, the county line runs down the middle of El Cerrito Creek.

If you wish to use the Caltrans map and consider the concrete path the county boundary for your personal listing convenience, feel free--it is not my list, but I would recommend not telling anyone.

Ethan Monk