Maeve, Kent, Ian, Jane, et al.,
I think the article (from 2011) Kent may have been recalling re: female
mimicry in male C.aeruginosus is referenced here:
http://www.newscientist.com/article/dn21138-zoologger-the-only-crossdressing
-bird-of-prey.html#.UoJvh3Avri0
The research in that case did seem to indicate advantages to the females and
"typical" males provided by the presence of the "faux males." Those birds
also had an advantage in that being 'accepted' as females, they didn't get
driven out of a territory the way a grey-coloured male would be.
In a paper in the Auk from 1986, Ethan Temeles of UCDavis presents research
indicating a prey base relationship to gender distribution in C.cyanus.
The Birding magazine article by Liguori and Sullivan which Maeve mentions
provides, IMO, quite excellent information on plumages.
And NOW --- I will put in a plug for the HMANA Winter Raptor Survey. As
Eric said, the Champlain Valley is where the action is for seeing birds of
prey during the winter months. As some of you know, I have been conducting
a standardized survey in the Addison area for 15 years. The data gathered
by such surveys across the continent can help researchers' investigations in
any number of areas such as the effects of climate change, human impact on
habitats, and yes, ratios of males to females, adults to juveniles, and any
number of other questions. While it is absolutely true that we cannot with
certainty sex Red-tails, for example, and the challenges inherit in aging
N.Harriers can contribute to a possibly skewed picture, some investigators
do feel that noting size differences (i.e. a designation of "female"
Red-tail means 'Large'; "male" = 'Small) or colour differences (i.e. brown
vs. grey Harrier) may be useful to a future research project.
All that aside, I invite you all to consider setting up and running a survey
route. The more data we gather, the better, and furthermore -- it's a fun
way to spend a winter day! Check http://www.hmana.org/winter-raptor-survey/
for more info.
Here's to Harriers! And Rough-legs and Red-tails and eagles and falcons
and....
Susan Fogleman
Campton NH
-----Original Message-----
From: Vermont Birds [mailto:[log in to unmask]] On Behalf Of Maeve Kim
Sent: Tuesday, November 12, 2013 9:02 AM
To: [log in to unmask]
Subject: Re: [VTBIRD] Northern Harrier
Kent and others interested in this topic - I've been hunting through old
birding magazines trying to find the article about male Northern Harriers
sometimes mimicking females in color - with no success. So I'm not sure if
the writer was describing birds in North America or elsewhere. I'll keep
looking.
I did find a related article that's pretty interesting, though, about color
variations as male harriers age:
https://aba.org/birding/birding452liguori.pdf
Maeve
On Nov 12, 2013, at 7:49 AM, Kent McFarland wrote:
> 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
>
> ____________________________
>
> Kent McFarland
> Vermont Center for Ecostudies
> PO Box 420 | Norwich, Vermont 05055
> 802.649.1431 x2
>
> [image: VCE Logo] <http://www.vtecostudies.org/>
> Visit Our Pages: [image:
>
Facebook]<http://www.facebook.com/pages/Vermont-Center-for-Ecostudies/569309
12454>
> [image:
> YouTube] <http://www.youtube.com/user/VCE14> [image:
> Blogger]<http://vtecostudies.blogspot.com/>
>
>
>
> 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
>>>>>>
>>>>>>
>>>>>> -----
>>>>>> No virus found in this message.
>>>>>> Checked by AVG - www.avg.com
>>>>>> Version: 2014.0.4158 / Virus Database: 3629/6824 - Release Date:
>> 11/10/13
>>>>>>
>>>>>>
>>>>
>>
|
