Posts Tagged ‘Nesting’

A friend of mine has been volunteering with the National Park Service to track the nesting activities of raptors in the Presidio in San Francisco, CA for the past twenty years. There are four species of bird of prey that nest in the park. They are Red-tailed Hawk, Red-shouldered Hawk, Cooper’s Hawk, and Great Horned Owl.

Information that has been collected include where these birds nest, how many nest in the park, when stages of nesting (breeding, egg laying, incubation, etc.) occur, how many chick fledge from each nest, etc.

This project has taken a wonderful turn this year with the installation of nest cams! My friend, and others, have been working with the Park Service to get funding to purchase and install nest live-cams on some of the active nests. One of the first such cams has now been installed on a Red-tailed Hawk nest that has been built between the branches of a Blue Gum Eucalyptus Tree. The live-stream of this nest cam can be found on YouTube HERE.

RTHA Nest Cam Capture

Male Red-tailed Hawk in the Presidio, San Francisco, CA incubating the one egg that had been laid at this point. Note thin, black barring that are restricted to near the base of the tail.

The pair of Red-tailed Hawks have laid one white, and lightly speckled egg in the nest as of 3/7/2018. The male and female can be distinguished by a few characteristics. The best is by tail pattern. The male has a few, very thin black bars on its red tail. These bars are limited to the base of the tail. The female, on the other hand, has those thin black bars on the tail that extend just about all the way down to the black subterminal band near the tail tip. Beyond these tail pattern differences, the male and female have different molt patterns on the secondary flight feathers, the male is slightly smaller than the female, and the male is banded!

RTHA Nest Cam Capture F

Female Red-tailed Hawk in the Presidio, San Francisco, CA incubating the one egg that had been laid at this point. Note the thin, black barring that extend all the way to the subterminal tail band.

I have already noticed a few interesting things after only checking in on the nest for a couple of days. One is that when the the male comes to the nest to give the female a break, he sometimes brings nesting materials to add to the nest. He does this even though the nest is complete and an egg has been laid.

So far, about 60 people have been watching the nest at any given time. I am sure that this number will go up, and it will be great to push it as high as possible, since I am also sure that the Park Service will be more inclined to install more live-cams if the public response is positive and strong. So watch the Red-tailed Hawks and see what is going on at  the nest!


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You are walking down a trail in a city park right here in the city of Berkeley. As it winds its way between huge boulders and beneath overhanging bushes, your attention is drawn up into a nearby tree by the sound of scratching. There, a squirrel is scrabbling up the trunk of a tree. As it ascends you notice a thick mat of sticks higher in the tree, way up near the tree’s crown. Is it the squirrel’s nest? The squirrel climbs higher, and then moves beneath the lower edge of the stick platform and then up around the side. As the squirrel begins to get on top of the mass of sticks, it is met with the oncoming rush of the beak and talons of a female Cooper’s Hawk. The mass of sticks is not squirrel’s home, it is the Hawk’s. The squirrel is in full retreat now, and the Cooper’s Hawk in full pursuit. The squirrel begins racing in the direction in which it can go the fastest, strait down the tree trunk. The Cooper’s Hawk immediately drops after it, skimming strait down along the bark of the tree. As the hawk gains, the squirrel jumps, letting go of the tree completely and free-falling into the bushes below. It is only then that the hawk gives up the chase and returns to her nest.

What you just witnessed was the defense of one of about a dozen Cooper’s Hawk nests in Berkeley and Albany. Cooper’s Hawks in Berkeley? That’s right. These roughly crow-sized predatory birds get along quite well with humans and the cities humans live in. They eat birds and small mammals which they often capture by ambushing their prey in dense vegetation and then chasing it down in a burst of speed. They are superbly adapted to this style of hunting with short rounded wings which give the speed while not getting hung up on foliage and a long tail which acts and a rudder allowing them to turn and twist through thick undergrowth and not lose their prey.

The ability to live well with humans is unusual for a predator. Most birds of prey are too sensitive to disturbance to live in such close contact with humans or need larger areas of open spaces in which to hunt than are available within such a human-dominated landscape as downtown Berkeley, but Cooper’s Hawks find a way. They are so tolerant in fact, that in Berkeley and Albany, more Cooper’s Hawk nests can be found per square mile than in any other recorded area in North America. They nest in mature trees in almost any kind of habitat from quiet city parks to busy city intersections. And Berkeley in not alone in being an urban area that has nesting Cooper’s Hawks. In California, most urban areas have populations. Outside of the state, populations that have been studied in some detail include urban areas of Arizona, Illinois, and Vancouver, Canada.

Beginning about 15 years ago, a group of dedicated volunteers have been keeping tabs each year on the levels of Cooper’s Hawk activity in Berkeley. The group, the Cooper’s Hawk Intensive Nest Survey (CHINS), has divided the 10.4 square miles of Berkeley into smaller units. Each volunteer takes responsibility for one of these units, and searches it to locate and track the presents of Cooper’s Hawks. Searching begins in late January when the hawks first arrive in the area back from their wintering grounds, and continue all through the breeding season until the adults and a new generation of young Cooper’s Hawks depart to return south in August. In between, many observations are made and recorded such as when the hawks arrive, when nest building begins and ends, how many young hatch and when, how many young fledge and when, what they are eating and how much, and finally when the adults and young disperse.

Some the information that CHINS has found is that while Cooper’s Hawks nest in greater density in Berkeley than elsewhere.Also, they are eating a lower number of species then in more rural areas, and of these fewer species a large portion (~33%) are Rock Pigeon, European Starling, and other species that are not native to California. On this limited diet, the hawks are able to breed just fine with most nests fledging 3-4 young each year.

The CHINS project is a branch of the Golden Gate Raptor Observatory, and both are examples of scientific studies made possible by volunteers from the community working to monitor and record raptor populations. Cooper’s Hawks, and birds of prey as a whole, can function as indicators of ecosystem health and stability. This makes them especially important and useful to study, and the fact that individuals from the community are able and willing act as citizen scientists and devote their time and energies to such an endeavor show both that such work can be done and that there is interest and support that such work be done.

To find out more about the CHINS Contact Allen Fish at (415) 331-0730 and find out how you can help protect your raptorial neighbors.

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While camping last week in the Sierra foothills, I got to witness a wonderful event; the first flight of a Common Raven. I have been fortunate enough to have seen many birds leave their nest for the first time and venture out in to the world. It always excites and inspires me. It is a view of the future, what will this new life include? It is a continuation of the past, linking each individual to their ancestors. It is a reminder that on this great web of evolving lineages, we are all connected to one another.

This particular first flight was, admittedly, not wildly successful. The ravens had built their nest in a large spruce tree that was just a dozen or so yards from where we were camped with a group of our friends. On Tuesday, the 17th of June, one of the young ravens decided that the time was right. It spread its wings and leaped out of the nest. It did not get far, as it glided right over our campground and crashed clumsily into a tree. it then attempted to flap its way higher up the tree, but only succeeded in knocking itself lower and lower until finally it fell out of the bottom branches of the tree and onto the ground about 4 feet from where my 1.5 year old daughter was playing with her friends! They all looked at each other for a moment. The kids looked at the raven with surprise and the raven look at the kids with the same expression. After a few seconds just staring at each other, the bird turned and hopped off through the trees. Rather soon, one of the adult ravens had found the wayward youngster and commenced yelling at the young bird until it found a tree with a lot of low branches and was able to scramble awkwardly up off the ground.

Over the next couple of hours, two more young ravens dropped out of the nest ending up scattered around that patch of forest. All seemed healthy and strong and began to explore their, suddenly expanded, world. The adults certainly had their work cut out for them as they tried to feed and keep track of the three young birds wandering through the trees, and the forest was loud with all of them calling back and forth to one another.

A pretty exciting and memorable event for all concerned!

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On Saturday, I spent about an hour-and-a-half with my three-month-old daughter wandering around a giant shopping center in Roseville, CA.  My wife was spending some time with some friends, and so my daughter and I took the opportunity to have a look around.  As we walked between huge box stores and along expansive parking lots I was impressed, as I often am, at how much animal life was finding a way to live in and amongst all the human impacts that exist in very urban areas.  House Finches were in the bushes all over the place and White-throated Swifts and Lesser Goldfinches were frequently flying and calling over head.

During our rambling, my daughter and I made two particularly exciting discoveries.  The first was finding a bee hive!  The swarm had built their hive in the nooks and crannies of a potion of a wall that have been made to look like pile rocks.  The bees were industriously visiting the wisteria vines, blooming not far away, and also coming in from much greater distances as they foraged for food for the colony.  I was pretty thrilled to find this hive, but was careful not to make too much a big deal about it when people were passing by because I was worried that someone would freak out and that the property managers would find out and spray the colony.  This was weird for me because I usually like to share sightings like this with anyone who is willing to listen, but here I figured that the best thing for the bees would be secrecy.  The second exciting discovery was a Bushtits nest!  The pendulum nest of lichens and spiders web was hanging in a small ornamental tree only about 6 feet above the ground.  The tree was in a little ally way between two humongous stores.  The two adults were very busy searching through the landscaped plant and bringing caterpillars and other insects they found back to the nest to feed their chicks.

Even though this was not a bird walk through some wild place it yielded some wonderful nature experiences, and was a wonderful way to spend some time.  It served as a terrific reminder that there is wildlife to be seen everywhere, and I look forward to continuing to share similar experiences with my daughter.

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As my wife and I were driving from our apartment to downtown Davis, today, we watched two adult, light-morph Swainson’s Hawks diving and chasing each other over I-80.  They were not acting especially aggressively towards each other, but rather were flying after one another in a more playful manner.  At one point, in the midst of their swooping and diving, they both gained a fair bit of altitude, flew straight toward each other, and locked talons!  They began to fall and spin directly toward the streaming highway traffic below.  For a brief moment, I thought I was about to witness a tragic crash, but then separated well before they actually got down to car and truck level.

I have only rarely seen this talon grappling behavior before, and never done by a pair of Swainson’s Hawks.  It was very dramatic!  This is usually done by birds of prey during the courtship period when two birds are setting up a territory and settling on each other to have babies with this year.  Late June is not when this kind of thing would be expected seeing as most all the birds are now in the hatching eggs stage of the breeding season.  However, just like humans, raptor pairs occasionally take a few moments out of their busy days to spend some quality time with each other.  This time serves to reenforce and strengthen their pair-bond, and may contribute to higher rates of nest success.

So, take a few moments, find your sweetheart, and reenforce your pair bond…and by that I mean that you should lock talons together and spin a little!

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We have two bird feeders hanging above the little patio of our apartment, and the most regular species that we have as visitors are House Finches.  We have them all year round with large numbers in spring and fall as the waves of migrants move through central California, a smaller number that stays through winter, and just a handful of birds regularly come to the feeders during the summer breeding season.  I strongly suspect that this is because the House Finches space their breeding territories out to where only two or three are close enough to allow the birds access to the feeders without them having to cross into a neighbors territory too much.

Yesterday morning one of the pairs was accompanied for the first time by two fledglings!  These young birds were capable of a decent amount of flight, thought they were still doing so somewhat clumsily, but they are completely reliant on their parents for food.  Each of the two fledglings picked one of the parents and followed that adult around from fence top to ground and back again begging for food all the while. The parents are more then skilled enough to fly up and land on the feeders, but the young ones do not yet have the skills.  Instead, the young birds simply give their begging calls and tremble their wings in the hope that this behavior will trigger the adult they are following around to turn and feed them.  The adults spent most of their time picking seeds off the ground and, when they had gathered a crop full, feeding the fledgling trailing behind them.  The fledglings watched the adults picking seeds off the ground with obvious interest, but little understanding.  The second most common bird at our feeders are Western Scrub Jays.  We have one pair of Jays that have claimed out feeders and let no other Jays come anywhere close to them.  This pair built a nest in a Cottonwood tree just across the parking lot from out patio.  It is about 20 ft above the ground on a branch that is particularly dense with foliage.  Today, when they came to the feeders, they were accompanied for the first time by one fledgling of their own!  This young bird also has the occasional tuft of down still poking out through its course Juvenal feathers.  The young Jay also seems to have about the same level of understanding of the world as the young House Finches seem to.  It follows its parents and begs for food.  It watches the adults gather seeds and break them open with apparent curiosity, but does not have any understanding of how to go about actually performing this task.  Instead, it follows its parents and begs for food with fluttering wings.

It will take a little while for any of these fledglings to figure out that those hard black things are sunflower seeds and that there is food inside them.  It will take them all even a bit longer to figure out how to actually open the shell.  A very fun process to watch.

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At the field house where my lab and office is, we have a number of Barn Swallow pairs that build nests and raise young each year.  This spring has been no exception with about half-a-dozen pairs building their mud cup nests under the eves around the edges of the buildings.  One of these nests is right above the front door of the office building.  A pair (I don’t know if they are the same individuals) uses that nest every year, and again, this year is no exception.  It is pretty dramatic to have these incredible flyers zooming in and out right over my head every time I go in or out of the building.  I would think that the regular flow of traffic would disturb the birds enough that they would not use this particular section of eves to nest under, but they do not seem to mind much.  They do fly off the nest each time someone passes by, but then they fly right back without delay.  Yesterday, I was coming out the front door, I found the two halves of a Barn Swallow egg laying on the ground directly beneath the nest .  It was split neatly in half, which is a sure sign that it broke when the chick hatched out.

Baby birds use their egg tooth to slowly chip away and weaken the shell from the inside.  They do this by shifting around inside the egg such that their head moves along the equator of the egg.  As they go around and around on the inside their egg tooth moves around and around along the same line eventually causing the egg to crack around the middle leaving the shell in two tidy halves.

I did not see these shell fragments when I first got the field house about three hours before, and so am pretty sure that one of the Barn Swallow eggs hatched between 11am and 1pm yesterday.  It is kind of cool to have such exact information on hatching times.  The adults will soon be even more fun to watch as they whip back and forth to feed their newly hatched babies!

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I came across my first family group of Bushtits of the year, today.  The group was comprised of what looked like three adults, which were probably the mated pair and one nest helper, and four young birds.  Bushtits are one of a number of species that include nest helpers in their reproductive strategy.  These helpers are usually young from the previous year that return to aid their parents.  Young birds that fledge from a nest early in the year also sometimes stay to act as helpers as their parents raise a second brood of young.  Since this family group that I found is so early I would not be surprised if the adults attempted a second brood.

A number of ideas about why young birds help raise their siblings are floating around.  One is that the young birds are getting valuable experience in raising babies, so that they will have better success when they do eventually go off by themselves.  Another idea is that the baby birds grow faster, and so fledge earlier, when there are more helpers to feed them.  A related idea has to do with what is called inclusive fitness.  This hypothesis says that the more individuals that carry a copy of a particular gene, the better, so helping relatives survive is actually a good strategy for preserving your own genes.  This is especially true if the individuals in question are close relatives, such as siblings, because there is a lot of shared genetic information.  A further idea is that good nesting territories are few and far between, so the helpers return to their parents territory and stay around in the hope of inheriting that nesting territory if and when their parents die or breed elsewhere.  This seems particularly possible in cavity nesting birds for which cavities have been shown to be a limiting factor in reproduction.  All these hypotheses seem reasonable, and they are not necessarily mutually exclusive, but few have been really well examined!  This seems to be an area that is ripe for some observations and experiments that might yield really interesting results.

So, who wants to put up a bunch of bird boxes and see what happens?

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The birds of prey, here in Davis, are in full nest-building mode.  Yesterday I followed an adult, light morph Swainson’s Hawk that was carrying a stick and so found my first Swainson’s Hawk nest of the year being built near the top of a redwood tree on campus.  This is the exact spot where a pair nested last year and is also where I saw my first Swainson’s Hawk this year.  I have no idea if this is the same pair that held this territory last year, but it does seem likely.

Additionally, today I saw a White-tailed Kite in some grasses on the ground.  As I watched, it took off with a bundle of dead grass in its beak.  I was able to follow this bird to my first White-tailed Kite nest of the year.  This nest is in the very top of a Valley Oak out near my lab.  The tree is along a ditch that acts as a riparian corridor, although there is no water on the surface, through the otherwise agricultural land that fills the surrounding area.

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