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IVORY-BILLS  LiVE???!  ...

=> THE blog devoted to news and commentary on the most iconic bird in American ornithology, the Ivory-billed Woodpecker (IBWO)... and... sometimes other schtuff.
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"....The truth is out there."

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Wednesday, February 17, 2010

 

-- Gender Imbalance or, Where Be the Girls? --

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Longer-term readers know that I share Cornell's Ron Rohrbaugh's recently-expressed pessimism about any recoverable population of Ivory-bills persisting in the Southeast. I don't doubt that Ivory-bills could hang on for another couple decades in some low steady-state numbers, but see no hope for them being around a century from now. Of course that goes for a LOT of bird species --- while the next few decades bear glimmers of hope, the next century or two do not (and the case for many mammals is even worse).

If Ivory-billed Woodpeckers made it into the 21st century one might surmise they likely persisted in an approximate 50/50 sex ratio to do so; OR, if the genders are skewed in any direction, one might expect it to favor females over males to bolster the species' survival chances. Thus, I'm often troubled by the high percentage of IBWO sightings that cite males, when gender is identified (in fact in the last 5 years I can't recall a single claim arriving in my email specifying a female) --- it's bad enough that male IBWOs and male Pileateds are the easiest ones to confuse, but moreover, there simply ought be more females in the mix if the species is out there. I'd guesstimate that maybe 70++% of credible or semi-serious sightings cite male birds --- but if Cornell or someone else has an actual breakdown of the figures I'd like to see it; maybe I'm off. Yes, there have been some good sightings of females and even pairs in recent times; they simply seem dwarfed by the number of male claims over that time. There could be plausible reasons for such a prevalence:

1) The vast majority of those claims may well be male Pileateds, dropping the actual IBWO male/female ratio back down to normality.
2) Females spend more time on the nest so possibly males are out-and-about, traveling more often and greater distances, and exposed to sighters more often.
3) Males are more visually striking and possibly noisier, thus perhaps more attention-getting.

Maybe it is that simple; but to the degree that male predominance of sightings actually reflect the ratio of Ivory-bills in the wild then it would be yet one more factor not boding well for a species that needs all the help it can get.

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Comments:
Around half of the "mountain lions" reported in Tennessee are described as black. Problem is, Felix concolor does not come in black. At least in the new world, "Black Panthers" are a political movement, not an animal. Stray dogs, however, are often black, long-tailed, and running rapidly away through the woods.

Most "Barrow's Goldeneyes" reported in the southeastern U.S. seem to be females; of course to the west and north where the species actually exists males are quite numerous.
 
Well, the skeptic in me has an explanation--both male and female of the Pileated Woodpecker have a red crest.
The preponderance of "male" IBWO reported is consistent with the idea that most recent sightings of "Ivorybills" are misidentified Pileateds.
(There are other explanations of course, but I think this is pretty likely.)
Remember: Extinction of the IBWO is just a hypothesis. Also, persistence of the IBWO is just a hypothesis. The question is, which hypothesis is more consistent with the data?
 
"The preponderance of "male" IBWO reported is consistent with the idea that most recent sightings of "Ivorybills" are misidentified Pileateds."

Most reports of Ivory-bills are passed through an initial filter (for identification and observer credibility) and are screened out - the remainder are the ones everyone talks about.

"The question is, which hypothesis is more consistent with the data?"

You tip your hand when you say "most" recent Ivory-bill sightings are misidentified Pileateds. The extinction hypothesis requires that every single sighting be either misidentification or fraud, while the persistence hypothesis requires that only a single sighting be an actual Ivory-bill. There are many detailed credible observations (Kulivan, Cornell 7, Hicks etc.) including multiple observers (Harrison/Gallagher) and even simultaneous independent observers (Agnew/Wolliver), so the data is clearly more consistent with the persistence hypothesis.
 
As far as I can tell, the vast majority of sightings since 2000 involving experienced birders produced no clear identification of gender. The Gallagher/Harrison sighting is just one example of this. This is hardly surprising, as most of these sightings were of birds in flight, presumably with crests folded. At least 6 sightings in Arkansas may well be of the same bird. It is difficult for me to see how you infer any kind of meaningful sex ratio from the data.
 
In the past I have mentioned a few times that the number of acoustical events and sightings that indicated pairs was significant. This was brought up to infer possible population viability.

CT never said a word against that inferrance but decided to bring it up now evidently attempting to dovetail with Cornell's possibly erroneous opinion.

In seconds we can think of several modern putative sightings (starting with Kulivan's detailed 5 minute look)or acoustical evidence that strongly indicates pairs are present. Pairs have been reported in at least 4 states by reliable observers, multiple times.

Also one should set up a heirarchical spread sheet of field reports. The sighting of a pair ranking much higher than even multiple sightings of only single birds assuming this data set is tempospatially related.

In other words if there were 3 sightings of single birds, regardless of sex and there was one sightings of a pair; all sightings occuring in a one year period in the same 10 s mile area, then one should not count that as 5 birds and pertinent here one should count that as a possible pair in that 10 square miles. It might also be argued that its one possible pair and one or more lone bird.

In addition many Picidae, I believe have an outbreeeding ethological mechanism. The females chase away their offspring males. This may have been observed in IBWOs (Sonny Boy, Fang?). This results in many male Picidae having to disperse much further than females.

CT also mentions some good points on why males may be more conspicuous. Regardless I agree with Fang that there is no sex ratio data that indicates one sex is well above the other.

More importantly there is plenty of evidence that there are multilpe pairs around, especially when you correctly and carefull treat sightings with weights as described above.

If population structure is properly looked at with the given data the IBWO will be considered to have several putative pairs about, mixed in with some possible singles. I see nothing unusual in our unpublished data of over 80 square miles of habitat to indicate there are not vialble pairs.

In fact I believe the putatitve population evidence nicely fits what a stable, but very small population should show.

Fred Virrazzi
 
Fred, that point about more males possibly being observed (off territory) due to their propensity for dispersal is excellent. Seems very plausible.
 
I can't tell whether Bill P. above is being tongue-in-cheek with his "Felix concolor" above, but puma concolor is the how the nomenclature police currently taxomonize these critters. Over the years I've also seen them referred to as "Felis" and "Pantera"; for the Gen X-ers, "Felix" was a cartoon cat who pre-dated his Holden Caulfieldesque nephew, "Fritz" (gotta a slip a tribute to J.D. Salinger in there, somehow).

And yes, I lifted my moniker from the feline nomenclature on this one, and not the rattlesnake's (even though I currently keep snakes and not cats). That happened when I got involved with some other locals to try to stop the stupid slaughter of these magnificent animals by those apparently in need of a testosterone fix.

There have been sightings of "Eastern panthers" for several decades now; I'm on the fence with regards to their credibility, and yes, as far as I know they don't come in melanistic versions.

Curiously, I did have a conversation last week with a lady from Massachusetts who claimed she and another motorist had seen a cougar by the road in that state (and not the human female variety thereof). She said they both commented to each other that nobody would believe them. And weirdly, the subject arose out of the blue when I was engaged in my day job and not discussing wildlife matters. This lady seemed genuine enough, so who knows?

Of course when I was attending wildlife hearings a few years ago I listened to the Southern Utahovian hillbillies insist they were being overrun, and we needed to increase the harvest to protect the deer herds.

For the record, I've never seen a mountain lion in the wild, nor a puma, nor a panther, nor a catamount, but I know they exist nearby. As for cougars, there's also the university mascot variety, plus the previously mentioned ones the young guys are always hoping to hook up with in the singles' bars.

Speaking from experience, though, wrestling with the bar species can become problematic . . .
 
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