[CT Birds] Moorhen mystery
Anthony.Zemba at gza.com
Thu Jul 21 12:15:52 EDT 2011
Roy, et al. sorry for the aborted email yesterday afternoon. And allow me to finish here:
Roy, you are absolutely right. And habitat suitability has a lot to do with how populations can handle/recover from those stochastic events. As habitats become less suitable populations may be impacted in a number of ways. Survivorship, fecundity, and other measures of a population's fitness may be negatively impacted by changes in habitat suitability. In some cases, certain biotic and/or abiotic factors may keep an emergent marsh in a dysclimax state. Out on the fertile South Windsor floodplain, that is not the case and emergent marshes succeed toward robust climax palustrine forested floodplain forest dominated by one or more of the following: Silver Maple, Eastern Cottonwood, Basswood, Sycamore (unless disturbed by farming). In the early days of the time period Paul was referring to, there was a lot more open herbaceous cover - both upland and wetland - to the north and the south of Station 43, and more open water (we have historic photos of the farmers keeping the old river channels open by blasting them with dynamite). From the air (to a Moorhen or otherwise) it must have looked like a large contiguous herbaceous stand of vegetation interspersed by the open water of a flooded old river channel. Over time, the reduction in agricultural intensity and the succession of and to palustrine forest has fragmented and reduced the herbaceous emergent cover type. Not only did the cover type change, but perhaps the hydrology as well as open water areas began to accumulate organic matter from annual senescence of the vegetation, and deposition of sediment from floods. Eventually, the marsh can become too shallow for Moorhen making them much more susceptible to predation, one of the factors you mentioned as a possible population demise. I am sure there were/are a number of factors working against habitat suitability for moorhens out there. This species is adapted to handle those changes, dispersing widely in search of suitable habitat, hence its wide distribution throughout North America and the Old world. Despite the large extent of the distribution, it is not particularly common throughout that range - at least in the US, and may be locally common only in some of the more suitable and extensive wetland systems. Their family (Rallidae) is known for their ability to disperse widely which makes them one of the more successful avian families to colonize oceanic islands (hence the presence of Moorhen on Hawaii, Guam, and some of the other Pacific Islands)
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 Roy Harvey
Sent: Wednesday, July 20, 2011 5:52 PM
To: ctbirds at lists.ctbirding.org
Subject: Re: [CT Birds] Moorhen mystery
> One can hypothesize that the wetland cover type may no
> longer be suitable for attracting breeding Common Moorhens.
Very interesting stuff, Anthony.
My idea is that a small, isolated population is always vulnerable. There will always be fluctuations in population. Habitat, weather, predators, migration, and just bad luck are just a few of the possible negative contributors. If the population is small, recovery from a negative swing can become impossible. It may not happen the first time, or the fifth time, but over time one of the downward swings can just swing too far. It is not like there are other nearby moorhen populations to balance things out with new members.
Beacon Falls, CT
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