What and where is the cavity?

The cavity is in a huge Eucalyptus tree where a limb “ripped out” about 20 years ago, pulling some of the inside of the tree with it. It is at least 2 feet deep and 18″ across with more room off to the back left. It is also hollow above (sometimes adults or chicks go up there), but we do not know how far up it goes.

It is about 40 feet up and we have a permanent ladder installed to make frequent climbs efficient. In theory, predators such as snakes or raccoons can enter the cavity, but to date viewers have not seen anything attempt to attack the eggs or chicks. Viewers have seen an occasional hummingbird flutter in.

Cavity location : 33°37’46.18?N,117°33’15.12?W in Google Earth or most other internet mapping sites.

How long do barn owls live?

From banding data, wild BNOWs live up to 12-15 years. If you are interested in longevity of other birds check out the Banding Lab’s Longevity Records. But more important, please understand that survival rates of BNOWs offspring (and this applies to all birds in general season to season) is extremely low – perhaps 5-10% at best make it to adulthood and breeding. Here’s why: Unlike humans who produce a few offspring (let’s say 1-6) over the course of their entire life time, birds produce these numbers of offspring numbers EVERY YEAR, many starting at their first year of adulthood which can be 1 year old. In the case of a BNOW pair, who for the sake of example might live ten years, they have the potential to produce 5-10 offspring EVERY YEAR over NINE years. Let’s say they average six/year. This means by the time they die they will have produced 9 X 6 = 42 young to replace the two of them. There is simply not enough room on the planet to accommodate all, especially given that there are millions and millions of birds doing the same thing every single year.

I don’t see owls – where are they?

When incubating eggs, the female will stay in the cavity for most of the night, leaving occasionally for reasons not totally clear to us. The male is often out all night hunting and will return with prey. The male may or may not spend the day in the cavity. If not, he will roost in a nearby tree, as many BNOWs do. As chicks hatch and grow, both adults will roost outside of the cavity during the day, and deliver food at night. Once chicks fledge, the cavity may go unused for sometime until this pair, or another pair, decide to use it again for roosting and breeding. However, chicks often use the cavity to roost during the day for several weeks after they fledge.

I want to learn more about the owls’ leg bands

Among other things, banding birds allows us to gain knowledge of how long they live and where they live and/or migrate.  Much of data that’s gathered from banded birds can come from band numbers read from birds that are found dead or captured and released.  However, the bands on birds the size of these owls can often be read with a spotting scope or, in this case, a zoom camera.

Birdbanding was formally regulated by the US Fish and Wildlife Service, but now by the USGS.  You must have a permit to band birds and this is also regulated by USGS.  Every band has a unique # on it and all bands are tracked in a database managed by USGS.  In addition, the proper band sizes are known and, in most cases, every individual of a particular species will wear the same sized band.  Last, raptor (birds of prey) chicks grow so rapidly that often by the time they are two weeks old their legs are large enough to comfortably wear and adult sized band

The adult BNOWs currently using the cavity have a US Fish & Wildlife Service aluminum leg band on their right leg. The male also has a “Monel” brand leg band on his left leg. Monel bands normally have the bander’s name and telephone number and a unique number.  It has been found that people will tend to more often report a band if there is a name and local telephone # on it.  Young BNOWs that hatch in this cavity will get a single aluminum band btw 2-6 weeks of age.  They normally fledge around 7.5-8 weeks.

If you find a bird with a band you can report it online or call the 800 # found on more recent bands.  In the past reporting was done by mail and you could simply send the info to “Bird Band, Laurel, MD”.  By any method, the Bird Banding Lab (BBL) will get back to you with information about when and where the bird was originally banded.

What sounds do barn owls make?

Barn owls produce a variety of vocalizations, although the ‘meaning’ of them is not always clear. For example, you may hear the female ‘rasping’ repeatedly, particularly before she produces and starts incubating eggs, but we do not know what, if anything, is being communicated. BNOWs also hiss and bill-snap when threatened.  They do not “hoot”.  Search Youtube for examples of BNOW sounds.

What is a clutch, and how big are they?

BNOWs lay one to up to a dozen or more eggs/year/per clutch (sometimes they have more than one clutch/year). A ‘clutch’ is a group of eggs laid in a nest at one time. Larger clutches sometimes result in not all chicks surviving. Two common reasons for this: 1) Not all the eggs always hatch. 2) When the female lays the first egg she begin incubating it, meaning development begins. It takes her 1.5 to 2 days to lay the next egg. So, for example, if she lays 7 eggs, it may have taken her two weeks to lay them all. They will hatch accordingly, each one after approximately 30 days. This means by the time egg #7 hatches, egg #1 (if it hatched) will already have 2 weeks of development under its belt. BNOW chicks can fly at around 8 weeks, so 2 weeks is a lot of development time and younger chicks are sometimes not strong enough to compete with larger, older siblings for food.

What do barn owls eat?

Barn owls eat a variety of vertebrates. Here, most are rodents, such as wood rats, mice or pocket gophers. For a list of all mammals found at Starr Ranch, see here. The adult female will bite off parts for the youngest chicks, but within 7-10 days chicks will rip off bits of prey on their own. By two weeks of age, they’ll consume a whole animal, as long as it is a small enough – such as a mouse.

Recent history of the cavity

2008 clutches and earlier: This cavity has been in existence for perhaps 20+ years. A large limb fell ripping out the inside of the tree to create it. It is unknown how long BNOWs have used it. However, we have banded chicks from this cavity for at least the last 8-10 years. The first cam went up around 2007 and was simply watched here at Starr Ranch. Webcam viewing began around 2008. In 2008 there were 5 eggs. The first 2 hatched several days ahead of 3, 4,and 5. and 3-5 didn’t make it.

2009: Info coming soon.

2010 clutches:
First clutch:
(Laying, Hatching, Band#)
Egg 1 – 01/02/2010 11:00, Hatch 02/03/2010 06:15, 907-04043 #1
Egg 2 – 01/04/2010 10:30, Hatch 02/04/2010 09:30, 907-04040 #2
Egg 3 – 01/06/2010 15:30, Hatch 02/07/2010 03:00, 907-04044 #3
Egg 4 – 01/09/2010 06:30, Hatch 02/09/2010 03:15, 907-04041 #4
Egg 5 – 01/11/2010 11:00, Hatch 02/12/2010 16:30, 907-04042 #5
These two did not survive:
Egg 6 – 01/13/2010, 17:30, Hatch 02/13/2010 08:30
Egg 7 – 01/16/2010, 11:00, Hatch 02/16/2010 01:45
Other 5 chicks all fledged.

Second clutch:
Egg 1 05/21/2010 08:00
Egg 2 05/23/2010 09:00
Egg 3 05/25/2010 01:00
Egg 4 05/28/2010 04:00
Three eggs hatched and all three chicks fledged in August. [top]

First clutch:
Egg#1 01/07/11 ~7:30AM  Hatched ~12:30AM 02/07/11
Egg#2 01/09/11 ~7:30AM  Seen ~ 2:00AM 02/09/11
Egg#3 01/11/11 ~8:40AM  Hatched ~ 2:20AM 02/11/11
Egg#4 01/13/11 ~7:20AM
Egg#5 01/15/11 ~8:05AM
Egg#6 01/17/11 ~8:10AM
Egg#7 01/19/11 ~11:00AM

What are these bees and will they hurt the owls?

European honeybees are commonly found on Starr Ranch. Although they were harder to find over the last several years, more recently they have become quite common again and hives are found in many natural cavities all over Starr Ranch. The comings and goings of the bees at this cavity are not a threat to the owls and occur from time to time. The bees are not in an aggressive mode – they are not defending a hive – and there’s not a lot exposed area on the owls that’s “stingable” anyway. They may “annoy” the owls, but that’s about the extent of it.

However, if the bees decide to start a hive in the cavity, then we will get to watch them build it and the owls will find a new spot. I make no apologies for saying upfront that I will not intervene should bees decide to take over the cavity. For one thing, there is not much I can do to prevent the bees from checking out the cavity. And if they do decide to build I’ve already learned that it is almost impossible to find a beekeeper willing to come out and move the hive to another location – especially one 40 feet up in a tree. And I will not exterminate them.