April 16, 2008 - Hatching imminent

Hatching: By now the chicks are nearing their projected hatch date. The chicks fill virtually the entire interior of the eggs that was once occupied by the yoke and the albumen.

Video: View Raptor Cam LIVE

A large air chamber known as an “air cell” exists at one end of the egg. If hatching goes well, the chick will shift into a “tucking position” where it places its beak between its body and its wing and then extends its beak into the air chamber and inflate its lungs. Prior to this time, the embryo has receive all of its oxygen needs through a network of capillaries that connect to a membrane inside the egg known as the “chlorioallantois” which imports oxygen from and exports carbon dioxide to the outside world.

Once the chick has broken into the air chamber it will begin to peck at the interior of the air chamber working its way slowly around the edge. The first break through to the outside world is known as ‘pipping.”

KWG / Audubon Raptor Cam

The process of pecking its way out of the egg can take a day or two. Chicks have a feature on their bill known as an “egg tooth” which allows then to break through the hard shell.

They also have a special muscle on their neck known as a “”hatching muscle” that gives them the strength to accomplish this task. This muscle shrinks once the chick leaves the egg.

Eggs may all hatch at the same time or one at a time up to 48 hours apart depending on whether the parents began incubating when the first egg was laid or whether they waited until the whole clutch was in the nest.

April 10, 2008

Today it appears that a large piece of paper or cloth has either blown or been carried into the red-tailed nest.

While the primary nesting material for red-tails is branches and natural materials, it is not uncommon for birds of prey as well as other bird species to also incorporate human garbage into their nests, particularly materials that allow them to weave their nests together. Osprey are particularly notorious when it comes to this habitat. Audubon. Sometime when you are out on the river, take a close look at an osprey nest through a pair of binoculars---you may be surprised to see that what appears from a distance to be all sticks actually is loaded with all kinds of unnatural junk.

Video: Hawk busy nest-building

Audubon deals frequently during the spring with hawk and owl nestlings that have become entangled in lines and other debris that their parents have incorporated into their nests. Another reason to always dispose of your garbage in appropriate receptacles! Fishermen should be particularly aware of trying to retrieve broken fishing lines.

Video: View Raptor Cam LIVE

April 9, 2008

The hatching of the Red-tails is immiment! Here are some answers to the questions folks are asking:

These Red-tails began building the new nest in January and began laying eggs around March 8th.

This year they are incubating three eggs, one more than in 2007. Red-tails typically lay from 1-4 eggs and the eggs are laid approximately 48 hours apart.

The birds can begin incubating the eggs as soon as the first egg is laid or they can wait until all the eggs in the clutch have been laid. If they begin incubating on the first egg, then the eggs will hatch 48 hours apart (known as an asynchronous hatch). If they wait until the final egg has been laid, then all the eggs will hatch simultaneously.

Both of the parents take turns incubating the eggs. Switch-offs can occur at anytime but rarely will one bird be on the nest continuously for longer than 4 hours at a time. The incubating parent will also stand up every few hours and turn the eggs. This is critical for proper development.

Video: Hawk rolls eggs in nest

Incubation will last between 31-35 days. We expect the eggs to begin hatching any time after April 10th. It will take another 41-45 days for the young to attempt their first flights. During this short six week period the nestlings will grow to be as big as their parents!

April 4, 2008

Visitors to the Raptor Cam this week noticed a dead pigeon near the nest, raising questions about what else red-tails might eat.

KGW / Audubon Raptor Cam

A pigeon is visible in the nest of a pair of Red-tail Hawks nesting in downtown Portland.

In fact red-tails consume a wide array of prey species that includes mammals, birds, reptiles and amphibians.

Two weeks ago, an Audubon kayak trip on the Columbia Slough even observed a red-tailed hawk perched and later flying with a fish in its talons.

While they usually kill their own prey, it is not uncommon for them to forage upon carrion as well. Red-tails have amazing capacity to adapt to the locally available prey base.

For the birds living in downtown Portland the most commonly available prey items are going to be pigeons and rats and both have shown up periodically as dinner guests on Raptor Cam.

April 1, 2008

Downtown Red-tails not only urban Hawks:

In addition to the pair of Red-tail Hawks we're watching nest in downtown Portland via the KGW/Audubon Raptor Cam, there are also several red-tailed hawks that nest around Portland’s Airport. The Port of Portland has developed an innovative strategy for managing Red-tailed Hawks that that utilize the area around Portland International Airport for nesting, foraging and migration. Traditional approaches throughout the nation for managing wildlife near airfields have focused on lethal control. However, the Port of Portland has developed a program for managing red-tails and other wildlife near PDX that focuses on non-lethal approaches. Audubon Society of Portland has worked with the Port since 1995 to develop and expand this program and many of its innovative and effective approaches are now being replicated at airports across the nation.

March 26, 2008

With the onset of unseasonably cold weather, many people are asking whether the red-tail eggs might be in jeopardy. Most likely the clutch will do fine during this cold spell, even if we get a day or two of light snow. The combination of the nest structure and incubating parent creates a remarkably stable microclimate inside the nest, even as the temperature and weather conditions all around the nest fluctuate from one extreme to another. The parents are able to maintain the eggs at around 99 degrees Fahrenheit by varying the length of incubation sessions and their positioning relative to the eggs. While the weather outside may seem extreme to us, it is well within the norm of what a wild hawk is equipped to endure.

If the eggs should cool slightly this most likely would result only on a longer incubation periods. Slight decrease in incubation temperature slow the pace of embryo development rather than kill the egg altogether. In fact the egg temperature would have to drop all the way to around 79 degrees Fahrenheit before development stopped altogether---for this to occur, the parents would have to give up incubating altogether. As long as the parents continue their normal incubation activity the eggs will likely do just fine.

Of course nothing is absolutely certain. Cold weather certainly can put more stress on the parents, increasing their daily caloric needs while simultaneously making it more difficult to find prey. Under particularly extreme circumstances the challenges of maintaining their own survival can cause parent birds to either be away from the nest for so long that eggs do become fatally chilled, the nest is exposed to other predators looking for food, or they abandon the nest altogether. These red-tails however are experience parents and the prey base (pigeons) surrounding the nest is very high so we would not anticipate this occurring under the predicted weather conditions. However, even if nest failure were to occur, it is early in the season and it is very possible that the parents would “recycle” and lay another clutch of eggs this season.

Some people have asked whether Audubon would potentially collect the eggs and incubate them in captivity if it appeared that the parents abandoned the eggs. The answer is “no.” Nest failure due to weather conditions is a very normal part of nature regardless of whether birds are nesting in the middle of the city or in a remote wilderness area. Evolution has prepared birds to deal with these types of factors very well and we try hard not to second-guess the birds. We are often called at Audubon by concerned citizens who are certain that nests have been abandoned, only to find a little while later that the parents suddenly return a little while later and resume incubation. Raptor Cam allows us all an intimate look at red-tails going through their nesting cycle---but like millions of other nesting birds across our region who are also dealing with this inclement weather, these red-tails will be left to their own natural instincts and abilities. Raptor Cam offers will offer a viewers a look at nature with all of its complexities, trials and tribulations.

March 24, 2008

The Red-tail mom is spending a lot of time on her three eggs right now, so here's a little info about the incubation process.

Embryos do not produce enough heat to compensate for heat loss from the egg, so the red-tail parents must incubate the eggs until they hatch.

During breeding season, females will often develop a “brood patch,” an area on the belly which loses its feathers and becomes engorged with blood vessels. This area comes in direct contact with the egg and allows the parent to raise the eggs temperature to almost the same level as its own body.

Many people assume that the biggest risk to the eggs is cooling. However, eggs can often survive temporary cooling. Overheating is a far greater concern---an increase of only a few degrees above the normal incubation temperature can quickly become fatal to an eggs.