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Maeve,
I thought this was just for one species in Eurasia, Circus aeruginosus.
Is there evidence for that here in North America for the species that
occurs here? I didn't see anything about it in the Birds of North American
account (revised in 2011), but maybe it was very recently discovered.

They do talk about polygyny in the Birds of North America account and say
it is more likely due to prey base rather than sex ratio. Our studies of
Bicknell's Thrush system, which is polygynandrous (a multi-male,
multi-female polygamous mating system), also pointed to prey base as a
major driver.

I think there are a lot of examples of polygyny in hawk-like birds:
Galapagos Hawk comes to mind. Some species have been found to at least
occasionally practice it: RT Hawk, Cooper's Hawk. In Europe I think
something like a third of raptors are known to practice polygyny.

A cool topic for sure! Thanks for bringing it up.

Kent

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Kent McFarland
Vermont Center for Ecostudies
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On Tue, Nov 12, 2013 at 7:03 AM, Maeve Kim <[log in to unmask]> wrote:

> In the past few years, scientists have discovered a fascinating wrinkle
> about sexual dimorphism in harriers. It used to be thought that there were
> many more harrier females than males. (One article I read said the ratio
> was 17:1 in some parts of the world.) Everyone figured this worked for the
> species because harriers are the only hawk-like bird known to practice
> polygyny (one male mates with several females). – But recently brown
> harriers have been found that have look like females (although a bit
> smaller on average) but are males. More research is being done, but the
> thought now is that there have always been more harrier males than
> previously recognized – that some mimic females in coloration, perhaps
> allowing them to sneak into other males’ territories without being attacked
> so they can mate with the Gray Ghosts’ females.
>
> One of the coolest things about bird research is that it keeps uncovering
> more and more questions! In this case: Do female harriers accept the
> odd-colored males? If so, why - when coloration is such an important
> “turn-on” in so many bird species? Are there other bird species that humans
> sort into male and female based on color but that nature has sorted less
> clearly? (Human beings love neat categories, but nature really doesn’t.)
>
> Maeve Kim
> Jericho Center
>
> On Nov 11, 2013, at 9:44 PM, Ian Almer Worley wrote:
>
> > Hi Eric,
> >
> > Are you saying that "gray-ghosts" can be either male or female?
> >
> > Thanks,
> >
> > Ian
> > ................................
> >> Hello VT Birders:
> >>
> >> In response/support to Jane's statement about seeing more adult male
> >> Northern Harriers in winter:
> >>
> >> In general, mature males in good health (the breeders) tend to drift
> south
> >> from their breeding territories as little as possible and return to them
> >> quickly in late winter/spring to secure it once again.
> >>
> >> Given that VT sits at the northern edge of the wintering range for
> Northern
> >> Harriers, we end up seeing a higher percentage of "gray ghosts" roughly
> >> Nov-Mar.
> >>
> >> We observe this with Northern Harriers because they are sexual
> dimorphic.
> >> This holds true for other species, like Red-tailed Hawks, but there is
> no
> >> way to sex them so it goes unnoticed. Even if you are banding a
> Red-tailed
> >> Hawk, it gets reported to the banding lab as "sex unknown" due to
> >> overlapping measurements.
> >>
> >> Wintering raptors in the Champlain Valley is one of the highlights of
> being
> >> a VT birder, at least from my perspective.
> >>
> >> Good birding,
> >>
> >> Eric Hynes
> >> Hinesburg
> >>
> >>
> >>
> >>
> >> On Mon, Nov 11, 2013 at 2:42 PM, Jane Stein <[log in to unmask]>
> wrote:
> >>
> >>> Broad-winged hawks are the only raptor that all leave for the winter.
> All
> >>> the others are partial migrants, and our winter population here is
> made up
> >>> of some year-round residents and some that have moved down from further
> >>> north to spend the winter.
> >>>
> >>> Somebody with better information please correct me on this, but it's my
> >>> impression that with Harriers, the females and immatures tend to
> migrate
> >>> more, and we often end up with more adult male "grey ghosts" during the
> >>> winter. I recall on one trip several years ago counting 7 adult male
> >>> Harriers in and around the Dead Creek area on what was probably an up
> year
> >>> for the vole population.
> >>>
> >>> Jane
> >>> (Shoreham)
> >>>
> >>> On 11/11/2013 2:25 PM, Barbara Powers wrote:
> >>>
> >>>> A Northern Harrier was sitting in a tree in our field. It later took
> off
> >>>> to hunt. I thought they had all left for warmer climes. Nice to see
> it up
> >>>> close.
> >>>> Barbara Powers
> >>>> Manchester Center
> >>>>
> >>>>
> >>>> -----
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> 11/10/13
> >>>>
> >>>>
> >>
>