Thursday, May 29, 2008

Pale Male and Lola's Eggs, Thunder, Reverse Sexual Dimorphism, Peregrines, and Fire Island Doves

Photograph D. Browne

Pale Male and Lola stand on the nest in the rain

I contacted Glenn Phillips the Executive Director of NYC Audubon and contrary to rumor Audubon does still plan for an egg retrieval of Pale Male and Lola's eggs as soon as the 927 swing stage goes into action for window washing and other building maintenance. That activity shouldn't be terribly long from now, and should still be within the window for trustworthy diploid test results.


(John Blakeman's essay on the Diploid Test and other relevant information coming up Friday, so stay tuned. )


I do hope that a very small sample of each egg,(keep fingers crossed for a male egg if they've been fertilized), can be collected in hopes of getting the DNA markers for Pale Male. Then we can compare his DNA with samples from other NYC Red-tails and once and for all find out who is related to whom. It's already too late to get a sample from Tristan, aka Pale Male III. Now, unfortunately, we will most likely never prove or disprove a relationship between Pale Male and Tristan. We mustn't waste anymore time.

Screen Captures of Thunder courtesy of R. of Illinois and KJRH TV

Thunder, looking somewhat peckish, scans the thermals looking for a parent bringing some dinner. Note that her crop is relatively flat so it's about time for a meal.

This eyass has the peachy breast that is often seen in the the Eastern United State. I'm very curious about the percentage of rufous to white breasts in Oklahoma. Of the urban hawks in NYC so far, most have the light rufous breast.

One eyass from the Fordham nest a few years back had the white feathered model. It's been suggested that perhaps the rufous morph might help the parents find their youngsters more easily.

The delivery arrives and it's a dead mouse which Thunder proceeds to kill soundly once again.

Practice makes perfect.


Food-- a fledglings chief delight in life.

Photo by D.B.
Red-tailed Hawks, Tristan and Isolde, 2006, of the Cathedral Nest.
A Grand Example of Reverse Sexual Dimorphism


Question: Are a female hawks toes always bigger than a male's toes?



All raptor species have reverse sexual dimorphism, ie. the female is larger than the male. Therefore it follows that the female's feet would be bigger as would the rest of her. But it's tough sexing a bird who is sitting alone. When seeing a bonded pair perched side by side then it's usually reasonably easy to decide their sex. Occasionally though you can have a big male and a small female and so they are close in size. The female will still most likely be bigger if one had them in hand and measured. The male and female also have a slightly different skull shape which some longtime watchers learn to recognize over time.



In Red-tails there is usually about a 25% difference in size. Though if you look at the Riverside pair they are much closer in size than Isolde and Tristan are in the above photo.

People like Jemima Parry-Jones can look at any raptor and tell you the sex and relative age. But then again she has worked hands on with raptors daily for many years. This is not to denigrate her expertise. I've seen her work and she has a spectacular touch and eye with these birds which is almost magical.

As to why raptors are reversely sexually dimorphic? There has been a tremendous amount of discussion as to why, as opposed to so many other species, that the female is bigger in raptors. Being larger for brooding has been discounted as has most of the other hypotheses.




Sexual dimorphism either way is a plus, for if one bird in the pair is larger than the other they can work the same territory and subsist on different prey. A Red-tail female can handily take rabbits but the males rarely do. But the male being smaller can live on fewer calories when prey is more scarce.

For instance, this was a very hard winter in the Midwest, at a certain point all the female Kestrels disappeared. They needed more calories than they could get in this area and went further south to find them, but as the males needed fewer, they stayed and looked after things on the home front.

I read a study done on a species of raptors in Australia, which for me held the answer to WHY ,REVERSE SEXUAL DIMORPHISM? Let me say though that there are others that do disagree but for me this answer does it.



I think that male Red-tails look around for a territory. They find something suitable and wait for a female to arrive. In the meantime there is a population of unbonded females looking around for a male with a good territory. If two females are interested in our male at the same time, I believe that the females fight each other for the male and his territory. The winner gets the guy and the goodies. It makes sense then that the bigger and stronger female would have a tendency to win, she gets the chance to reproduce and propagates larger females who in turn will likely win mates with territory in the future.

I found this reinforced at least for me in the behaviors of Pale Male and Lola. During breeding season, Red-tail intruders will fly near the nest area while Lola is brooding the eggs. In some cases, she keeps sitting and Pale Male will rather gently "herd" the visitor out of the territory. We surmise these visitors are their young from a previous season. They recognize the son or daughter and usher them away from the nest.

On other occasions, Pale Male will be more aggressive in chasing the intruder out while Lola looks on. But then there are the instances when a Red-tail will arrive, Pale Male goes after it, and suddenly Lola turns into a Valkyrie, comes off the nest like a rocket and seriously goes for the intruder. The poor intruder usually then high tails it out of the area in fear of live and limb. I surmise these visitors are female and Lola doesn't want another female anywhere near her mate or in her territory--at all, ever. She takes the appearance of another female very personally.


Rob Jett of The City Birder made an observation that also supports this theory as well. He has been watching a bonded pair of Red-tails in Brooklyn for some time. One day during the courtship season, there happened to be a Red-tail female, that was unreleasable in an avian enclosure topped with a roped covering not far from the hawks he watches.. The pair heard this enclosed female calling and both went to investigate. The male sat on the sidelines while the females attempted to go at each other through the netted top of the aviary. A mini-demonstration of the female vs female battles that may well go on frequently behind the scene.


Then there are the cases in which a pair of Red-tails encroach on the claimed area. In these cases, I assume, because two birds must be dealt with. Lola comes off the nest in her Valkyrie mode, both she and Pale Male screaming, while Pale Male makes for the nest to protect the eggs. Why? First of all Lola is bigger and because while Lola is dealing with one RT, the second might come and despoil the nest. Pale flies to the nest and stands over the eggs, while puffing up his feathers and even doing raking of the twigs with his talons in a very butch manner. If because of the vagaries of the fight, Pale Male has a better angle for attack or Lola is tiring and at some point needs a hand, he'll come off the nest, go after one of the pair and Lola will fly back to the nest for a breather. In a pitched battle these switches can happen numerous times. I take these instances as a possible invasion that is an attempt to steal the territory away from PM and L. It doesn't work. In fact it's never even been close

Photograph of Rochester Peregrines courtesy of Froona.

From contributer Karen Anne Kolling--"Why parents get tired... I'm guessing this is the Dad. "


Photograph by Brett Odom
Donna,

I was out on Fire Island over the weekend and I took several photos of two Mourning Doves displaying. At first both doves were displaying exactly the same as the one on the right, but the left one changed his posture before I could get my camera out.

Have you seen your doves in WI do this?

Is this two males competing for a female off camera or is this a male and a female? Or are they just attempting to warm up in the sun? I was able to get photos of a few different postures, all of them with their wings and tail spread. I only saw this behavior once for the five days I was out there.
Brett


Hi Brett,


No, I haven't seen Mourning Doves in this exact posture before. As these two are hunkered down I doubt the feather position has anything to do with any aggression. Doves aren't much for aggression anyway. All I've seen two males in breeding season do in response to each other is that one will do a little hop towards the other and the second male then backs off a foot or two and they both go back to their business. Or sometimes at a feeding area, they just keep their backs to each and pretend they are the only male there.

I have seen other birds spread their feathers to dry them in a somewhat similar feather position but not in the snugged down posture. But then again doves are very prone to lowering their bodies onto their feet. Doves in Wisconsin, remember it's usually a little chilly if not downright cold, tend to dry themselves in the sun with one wing up and feathers raised instead of spread.

I'm wondering if these birds aren't spreading their wings and tails in the sun, not only for a sunbath but perhaps as they are on Fire Island which is very sandy, perhaps they spread their feathers so that any moist sand that has adhered to their feathers will dry and fall off?

Any other possible theories or similar sighting, anyone?

Donegal Browne

3 comments:

Yojimbot said...

Yes...Ive seen that posture before. They are definitely sunning themselves. Ahhhh, sunshine!

Anonymous said...

Hi, I have seen ring-necked doves doing that posture here in South Florida, in my backyard. I have not been able to figure out what it's about. It doesn't seem connected to aggression, or mating. It looks like they're relaxing. No other dove looks bothered, or agitated, or excited by it. Thanks for your site!

Donegal Browne said...

Thank you James and South Florida for your observations and nifty explanation. I do most of my Mourning Dove watching in Wisconsin. I do it daily and yes, doves are very partial to sunbathing. But these Wisconsin doves never seem to spread their feathers while catching those rays. They hunker down on their feet and face the sun. They keep their feathers smooth, and their wings and tail folded.

Perhaps it never gets hot enough here for them to be cued into spreading their feathers?

Fascinating.