This may be the last dollop of photos for a while, depending on how much time I have on the road. But today we have a great series from Bruce Lyon, continuing his story of the Northern Harrier nest I posted about several weeks ago. Here are his pictures and notes; the photos are stunning, and be sure to read the text:
I have been following nesting Northern Harriers (Circus cyaneus) north of Santa Cruz in California. This batch of photos is a follow up to photos and descriptions Jerry posted on June 7.
The male provided much of the family food, particularly during incubation and the early chick stage. Male harriers almost never go to the nest but transfer prey items to the female in the air. The next two photos show a prey transfer. The female (brown bird) chased the male (gray bird), who has a mouse (you can see it under his fanned tail). In prey transfers, the male drops the prey item when the female is close enough, and she then quickly snatches the prey item. In the particular transfer shown below, the male seemed to drop the mouse a bit early and the female had to go into a nose dive to get the mouse (second photo). It took me a lot of attempts to finally get a decent set of images of transfers because it is difficult to predict where the transfer will occur and they are not always very close. The two photos of the prey transfer were taken with my Canon 500mm F4 lens and are heavily cropped.
Female returns to the nest with the mouse. I was able to watch the female calmly coming and going to the nest simply by throwing some camo netting over myself and camera. As far as both the male and female were concerned, I disappeared once the camo netting was over me:
Female coming in to the nest with a lizard (a Western Fence Lizard [Sceloporus occentalis] I believe):
The harriers often had what I interpret as a ritualized copulation interaction. Often when the male returned to the nest area and the female was not on the nest but perched on a bush, he would land on her back for a second, crouch down and then take off. I saw this happen about a dozen times and watched carefully and never saw anything resembling a real copulation. I have no idea whether this serves any function, but in the old days this behavior have been interpreted in context of ‘maintaining the pairbond’. The next two photos show one of these pseudo-copulations:
The harrier nest had a fairly high rate of ‘brood reduction’ (chick death). Of the five chicks that hatched, only two survived. Often extreme brood reduction like this is associated with asynchronous hatching, where different eggs hatch on different days. David Lack, the influential English ornithologist, proposed that brood reduction is a mechanism that allows birds to adjust their family size to an unpredictable food supply (they have to choose the number of eggs to lay before they know precisely how much food will be available for the kids). He also suggested that asynchronous hatching provides the parents an efficient mechanism to trim the brood size to match food supply because the smaller, later-hatched chicks are the first to go if there is not enough food for all. The harriers seem to fit this pattern—two chicks hatched on the first day, two chicks hatched on the second day and the last chick hatched later (presumably the next day but I did not check the nest for a couple of days). Since the chicks were not tagged I don’t know which chicks perished but there was a very clear size hierarchy early on and I am pretty sure that the two survivors were the chicks that hatched on the first day. It is well known that female harriers, who do the actual chick feeding at the nest, do not preferentially feed the smallest chicks—the largest chicks would have a competitive advantage in grabbing food due to their larger size. Here is the first day of hatching:
When I next, checked the nest a week after hatch there were four chicks left. The chick on the right had recently swallowed a large mouse intact and the tip of the mouse’s tail is sticking out the chick’s beak:
When I next checked the nest, three weeks after the first eggs hatched, there were only two chicks left:
One month after hatch the chicks were developing the gorgeous rufous coloration of juvenile harriers:
Almost 50 days after hatching the two survivors are full grown and could fly very well:
After the chicks fledged I made a discovery that could explain the extreme brood reduction, and it also provides a an example of an idea I have been thinking about for awhile. I observed the male fly by the nesting area with a mouse. The female flew up to him and I expected a prey transfer, but it did not happen. Instead, the male kept flying. The photo below, of the male with a pocket gopher, illustrates what I saw but is not the actual event. Roughly a mile further south a second female flew up and got the prey item from the male—he had a second family! I eventually found the second nest and it contained four large chicks ready to fledge. This nest was about three weeks behind the first one but since it had double the family size I suspect the male was bring most of his prey items to this nest.Polygyny, where one male has several mates, is fairly common in harriers and individual males can have ‘harems’ of 2 to 5 females. Back to the issue of brood reduction, I now wonder if the first female laid a clutch size that would have been ideal had her mate invested only in her nest. David Lack proposed brood reduction to deal with ecological uncertainty but I have been wondering for some time whether social uncertainty—specifically whether feeding by the male is predictably or not—might play a role in some species. Then the harriers provided a possible example. Natural history at its best!
Great photos. And nice lens. 🙂 Harriers have a nest just across the creek from my house and I see this behavior all day long. This is a big year for voles and they don’t seem to have any problem catching food.
The nose dive & coming in for a landing pictures are fantastic!
IMO, they’re all fantastic! 🙂
Sure, make me look stingy with the compliments. 🙂
Well, I’ve heard that the harder they are to come by, the more they mean to the recipient…tap, tap, tap…<– me, tap dancing…
Fantastic pictures! Could the disappearance of chicken be due to predation (by some snake, in Europe I would think about Natrix natrix)?
Gorgeous birds, gorgeous photos, fascinating narrative. Thank you for sharing Bruce.
My daughter would like to work with you. Looking for a young apprentice by chance? 🙂
Very impressive stuff.
There are some pigeons in my garden but it isn’t really the same.
Spectacular photos of those wonderful birds and I thought the essay about brood reduction was really interesting. I always thought that the number of survivors from a clutch was determined entirely by food supply.
Well, if the male wasn’t delivering enough food, then that was the case.
Fascinating. These photos are gorgeous. I am thankful for the vicarious experience with these magnificent birds.
Around my neck of the woods, which is no woods at all, the superabundance of rain has changed the central Oklahoma landscape a bit. We have pears and apricots growing on ornamental trees. Garter snakes are quite sizeable due presumably to the abundance of food sources. We have families of geckos living in and around the house. Bunnies are hopping all over the place in ours and our neighbors’ front and back yards. Neither sight has ever occurred this deep into town, at least in my experience. There was a largish turtle on my porch the other morning, which I failed to photograph, like a dummy. It has been an interesting summer to this point. I need to make a habit of capturing photos of this wildlife propagation when feasible and submitting them to Jerry for possible ‘Wildlife Photos’ posting. I would be terrible at identifying species, though, so hopefully posting them would be an opportunity for someone to share their expertise.
Nothing I like better than an ID quiz. 🙂
they have to choose the number of eggs to lay before they know precisely how much food will be available …
Choose? They choose??
I should have responded earlier but hopefully late is better than never. ‘Choose’ was sloppy shorthand language on my part. Birds have built in physiological and sensory mechanisms that allow them to use information from the environment (and their own bodies) that determines the number of eggs that are laid. In behavioral ecology this is referred to as decision making, but this does not imply that the organism is necessarily making a conscious decision. Feeding experiments with wild birds have shown that food supply can be one such cue the birds use in determining clutch size but the specific cognitive and physiological mechanisms that connect food supply to the number of eggs laid is not well understood, as far as I know. Does this answer your question?
Wonderful series of photos and fascinating narrative. Thanks!
As a kid growing up in CA, we always called the fence lizards “blue bellies”. Those suckers are hard to catch…much respect for the Harrier’s hunting skills. They are obviously equal opportunists when it comes to their prey…do they also catch fish?
Thanks for this series of photos and the captivating commentary.
Fascinating story and exquisite set of photos, Bruce! I SO appreciated all the illustrated harrier lore.
A couple of the nests I followed off & on this season also showed brood reduction– European Kestrel and Great Horned Owl. Apparently the older chicks eat the younger, which makes perfect sense, but it is jarring to see 5 cute little chicks huddled up together in the nest box, only to return a few days later and find only two!
I wonder if the male harrier in any way “knew” that the second female was a safer bet for chick raising, and thus fed her more? E.g., perhaps the first hen was also a first-time, unproven breeder. So many intriguing angles to consider!
Second time I’ve not found my comment after hitting post, then refreshing, so I suppose both are going to show up eventually, as WP is wont to do. If so, my apologies.
Spectacular shots. Looking at these almost feels like we invade their privacy.
Thanks for this wonderful post, Bruce. The ‘true facts’ are very interesting and the photos excellent.
Fabulous shots and a great narrative. It’s a tough life if the food supply is not up to it as I assume that if it had, and no diseases and such, more of the observed nest would have fledged as well.
Really great pictures as well as natural history. We here in south central Iowa are having a really wet year (5 1/4″ a couple days ago and rivers up 18′ in some places. Vultures are doing well, but our raptors are harriers and red tails (that’s it). When we moved here there was far greater diversity and the kestrels have disappeared entirely from this area. Our first year here (2005) they were all over the place.
We do get an occasional sharp-shin haunting the bird feeders.