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Posted by C.K. Borg on 09:54:41 10/24/08
Folks interested in receiving a pdf of the recently peer-reviewed Journal of Raptor Research article that specifically addresses the data discussed in David LaPuma's recent post should please feel free to email me... and I would be happy to send you the article as an attachment. However, below is a message I recently received from Casey Lott further explaining these population estimates. The simple fact of this matter is that the Science doesn't support our concerns. Rather this is really a matter of the heart. I encourage anyone interested to send FWC an email.
Best,
CKB
From Casey Lott:
"All of these estimates used existing data (and some simple assumptions) that are laid out in detail in my 2006 paper in the Journal of Raptor Research describing the Florida Keys raptor migration site... The region you referred to as 'eastern North America' is defined pretty broadly in my paper (I called it the 'boreal/eastern' population). In case this number seems high for the eastern US, or even the eastern US and eastern Canada, which might be implied from 'eastern North America', these estimates refer to a much larger area.
As I defined it in my paper, the 'boreal/eastern population' includes all tundra breeding peregrines from Alaska, Canada, AND Greenland, as well as peregrines from the US east of the Mississippi. Given decades of banding data and tracks from satellite-tracked birds, these are the birds most likely to migrate through the Florida Keys. This definition of a 'population' excludes western peregrines from the US, Canada, and southern Alaska that are unlikely to migrate through the Florida Keys.
The estimate for the entire North American population, referred to in your email, includes all of these birds (Alaska, Canada, Greenland, and the lower 48), but not peregrines breeding in Mexico.
For those that don't end up reading the paper, the annual peak population estimate for North America is for the end of the breeding season, after young have fledged, before fall migration. It represents the maximum number of birds that may be available to migrate across North America. Since some young peregrines die after they fledge but before they make it very far south during migration, it is probably a high estimate for the real number of fall migrants. The estimate of 24,000-39,000 birds is based on the total number of territorial breeding pairs (minimum estimate of 3,434, maximum estimate of 4,360), plus an assumption of one non-breeding adult 'floater' per breeding territory (which comes from the peregrine monitoring literature), plus annual productivity estimates of 1.3 (minimum) to 2.5 (maximum) young per territorial pair. The range of 24,000-39,000 birds comes from multiplying the minimum pair estimate by the minimum productivity estimate (the low number) and the maximum pair estimate by the maximum productivy estimate (the high number). Pair and productivity estimates were based on an extensive literature search when I prepared this manuscript in 2005. Population size has most likely increased a bit since then."
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