Wednesday, May 05, 2010

ENV: Common Raven nest follow-up May 2nd

I returned to the Common Raven nests at Big Springs Ranch on Sunday May 2nd to check the progress of the chicks. I was able to get additional photos and take some film while there. In a note to the Texas Ornithology listserv, and biologists i knew would be interested, (see below), i made a mistake i need to correct. There were two brief feeding bouts i was able to both photograph and film and, although, watching all this through a viewfinder, i thought that two different chicks were fed in these encounters. However, on watching the film, it is obvious that only a single chick was fed both times.

UPDATE: i visited again on 7 May 2010 and all the chicks had left the nest and were not located in about 30 minutes of observing at the nest site.

In addition to the notes here, i am appending a series of pics from May 2nd. And below those is the video, followed by a log of the important events in the film for those who don't want to sit through eight minutes of sleeping chicks.

The post that first noted the discovery of the dual nests is copied below and can also be found here: http://milkriver.blogspot.com/2010/04/env-big-springs.html

Special thanks to John Arvin, Chris Merkord and Jack Eitnear for comments on the previous notes.

Notes on Raven Nests, Big Springs Ranch, 23 April 2010
On Friday i showed the Nature Quest group the Common Raven nest on the honeycomb overhang above tablerock, and one of the participants noted that there appeared to be two nests. Sure enough not only were there two nests (for the first time in my observations at the Ranch), but there were two young in one nest and three in the other. In all my years i have never seen this, thinking Common Ravens to be territorial. I have done some preliminary searches and have not found any specific instances of Common Ravens communally or colonially nesting. However, African Dwarf Ravens do so, and there are records in North America for both American Crows and Northwestern Crows, and i found indications that Fish Crows do also. But there is also specific research on Chihuahuan Ravens to determine if any takes place, which found them too territorial to allow for it. Although they do not keep other nesters from feeding range, they do maintain a minimum distance between nests even among former nest helpers from previous generations. I will continue to research to see if there are records for Common Raven. We watched these birds at some length and found that when an adult came to the nest, four times over the days we observed, that they always fed the young in the leftmost nest. At one time, the two birds from the rightmost nest made their way to the other nest along a small ridge but were ignored by the adults. In addition it was clear that the rightmost birds were significantly older than the leftmost birds, being close to fledging (indeed one was not in the nest on Sunday), and standing on the rim of the nest. The other three were hunkered in the nest until an adult arrived, and while fully covered in feathers, still had bright yellow gapes and did not appear near ready to fledge. I guessed a difference in age of at least one week. Pictures of the nests are posted at http://milkriver.blogspot.com/2010/04/env-big-springs.html


Additional notes on the dual Common Raven nests, Big Springs Ranch, 2 May 2010
i was able to return to Big Springs Ranch today and spent considerable time at the dual nests i described last week. the two older chicks, one of which apparently left the nest for the first time last Saturday/Sunday, were present and flying about with an adult in attendance, landing on bare limbs and the cliffside. i watched the adult land one time near a chick with what looked like food from a dump (orange rind?). what exchange there was was obscured by trees. the three chicks from the other nest were also still present, and more or less confirming my opinion last week that they were about a week behind the others, were at or near fledging stage. two were initially perched on a ridge about eight inches above and "east" of "their" nest, the other one was below and some fifty feet west on a ridge along the cliff, where it may have ended up after a test flight, or it could have fallen/rolled from the nest and then walked west. in any case, they were testing their wings frequently with flaps and hops. a pair of adults, one significantly larger [likely the male], one deeper voiced, flew in twice while i was present, with the larger bird feeding one chick near the nest on one trip, and the second chick near the nest on the other trip [corrected now, after watching the film, to feeding the same chick as before]. the smaller adult simply sat by. the larger bird flew within feet of the third chick down the cliff face on both visits, but i did not see it stop there or feed that chick. i have additional pictures from today, and i also have film of one of the feeding entries. i will post all of that some time this week, i am under the gun on a couple of work projects right now. besides getting further insight into the age difference of the young today, the other new information was the total number of adults, at least three (only one was seen last week), and that a different adult attended the fledged birds than the pair attending those still at/near the nest. beyond that who knows the relationships among these birds. i will be returning again Thursday and Friday of this week, although i will be there for work purposes and may only have a short time to check the nests.


New pictures at the nest, 2 May 2010
clicking on the pictures enlarges them





















Video of the Raven chicks being fed, Big Springs Ranch, 2 May 2010



Film notes

no sound on this because the wind was blowing strongly and not much can be heard beyond mic noise

the traditional nest from past years is on the right and the new, second nest is on the left

0:09 view of dual nests built in remnant honeycomb limestone below cliff overhang

0:14 close on the two chicks from the second, later nesting, still at the nest site

0:45 close on the third chick from the second nest, below and west of the nest site, after perhaps testing its wings, or falling from the nest

1:26 distant look to zoomed in of nest site on cliff point overlooking the upper Frio River

1:40 view from below nest downriver on the Frio River at junction of Big Springs outflow

2:14 chicks straighten up and begin stretching and preening in response to adults calling in the distance -- interesting that an adult and the two chicks from the first nest were in the area and had been calling repeatedly, but only when the distant adults on their way to this nest were heard did they stir

2:41 the first feeding bout caught on film, the larger adult bird flies in feeds the closest chick and then flies out within about 4-5 seconds

4:46 the second feeding bout, the larger adult flies in first and lands on their nest, then the second adult flies in and lands between the nests. the first adult then hops up to the level of the chicks and feeds the same birds as a couple minutes previously, both adults leave within 30 seconds of arriving

6:07 the chick that had been fed hops down to its nest then makes its way across the ledge to the other nest

6:38 the second chick hops down to its nest then makes its way between, where it lingers a while

7:05 jump cut to both birds in the "other" nest

7:14 clips of the third adult in the area, the one attending the two chicks from the "other" nest, as it hops along the ledge, one of its chicks was perched, obscured in a tree above it

7:35 another clip of the third chick from the second nest


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