[CT Birds] population estimates (long .... and probably boring)
Anthony.Zemba at gza.com
Tue Oct 4 12:17:50 EDT 2011
I have not read the publication yet myself, and perhaps I should reserve comment until I do so at the risk of sounding off the mark here. But perhaps the problem comes from a failure to take into consideration the special habitat attributes of the two species in question. For instance, Red Maple swamps are by far the most common Palustrine Forested wetland in CT. Four-toed salamanders inhabit Red Maple swamps, but Four-toed salamanders are by far not the most common Caudate in CT and are in fact absent from many Red Maple swamps. They likely require a certain special habitat attribute (perhaps presence of a Sphagnum layer?) within the Red Maple Swamp for the swamp to be suitable habitat. If one was to sample a Red Maple swamp where they were locally abundant and then use those results to estimate state population by extrapolating over the area of known red maple swamp coverage in CT, one would be way off base. I fear the same may have happened here. Yes Acadians and Ceruleans are a forest interior species, but as most birders known, not all forest interiors have Acadians and Ceruleans. They are likely forest interior specialists that require a special habitat attribute. As an example, Acadians that I have encountered in the forests of eastern CT have all been found within interior forests but within the area of the forest that is bisected by riverine upper perennial streams. I suspect that their breeding territories are centered on or about these drainage types. If one was to conduct point counts across a forested landscape bisected by such drainages and get a density of breeding Acadians and then extrapolate that across the entire forested watershed one might generate erroneous results for as one moves higher or lower in the watershed, stream density changes too. (e.g, higher in the watershed the streams become intermittent or originate from a palustrine forested wetland or groundwater discharge seep, and lower in the watershed they diminish as drainages join to form larger, lower perennial streams).
In the case of Ceruleans, I believe that they require a special habitat attribute or combination of attributes that may be based upon a specific forest structure produced by certain vegetation associations age or some other structure influencing factor. The presence of a shrub or sub-canopy layer is likely a factors based upon my casual observations (e.g., saw-timber sized mature forests with a developed canopy but with enough light reaching the forest floor to sustain a subcanopy or shrub layer).
Certainly three seemingly productive (or at least frequently birded) spots in the state for Ceruleans (River Road in Kent, Hartman Park in Lyme, and Boston Hollow Eastford/Ashford have very different vegetation species compositions, but the overall structure may be similar. Whatever the preferred combination of attributes are, they would by no means be uniformly distributed over all of CT's forest interiors as slope, aspect, elevation, hydrology, soil type, depth to bedrock, age class, coverage, etc, would change with location within the forest influencing forest structure.
Anthony Zemba CHMM
Certified Ecologist / Soil Scientist
GZA GeoEnvironmental, Inc.
655 Winding Brook Drive
Glastonbury, CT 06033
ONE FINANCIAL PLAZA
1350 Main Street
Springfield, MA 01103
anthony.zemba at gza.com
From: ctbirds-bounces at lists.ctbirding.org [mailto:ctbirds-bounces at lists.ctbirding.org] On Behalf Of David F Provencher
Sent: Tuesday, October 04, 2011 11:32 AM
To: Chris Elphick; ctbirds at lists.ctbirding.org
Cc: chris.elphick at uconn.edu
Subject: Re: [CT Birds] population estimates (long .... and probably boring)
As you know, my background is technical and I am (sadly) not unfamiliar with statistics and the protocols (including their weaknesses) for censusing birds. Additionally, my birding is very rarely done at the known birding hot spots. For me, walking and hiking are as important as the birding, so hiking boots and sweat (and often blood) are as much a part of my birding as binoculars are. Being a hard core hiker has given me a pretty decent ability to judge distances in the woods as well, which helps to more accurately assess population densities. I agree that there are more Ceruleans breeding in CT than a lot of birders may realize (I mentioned that to a few correspondents privately yesterday) and southeastern CT has a good distribution of them. Although the sites tend to be scattered and of very low population density.
I believe these two numbers are significantly off the mark high, especially with regards to Acadians. If there were that many Acadians in CT they would be the most common forest interior flycatcher in many places. To put it simply, they are not, they are uncommon to absent across all the areas of CT forest I hike, and I hike over most of the state. I have never found anything like the density levels these numbers represent for Acadians, and only in a few places for Ceruleans. I realize you could have written ten times as much info on censusing protocols and statistics as you did (thankfully you didn't!), but I think this may have been an "oops" moment in a very important and needed published work. Clearly you had reservations on this data at the time of review. On balance I think the strength of this excellent publication far outweighs its few weaknesses. Hopefully, as we move forward, the quality of the data will get even better.
From: ctbirds-bounces at lists.ctbirding.org [mailto:ctbirds-bounces at lists.ctbirding.org] On Behalf Of Chris Elphick
Sent: Tuesday, October 04, 2011 8:17 AM
To: ctbirds at lists.ctbirding.org
Cc: chris.elphick at uconn.edu
Subject: [CT Birds] population estimates (long .... and probably boring)
A few responses to your question ... a bit long-winded I'm afraid ....
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