Monitoring @ BCCER

Another acronym! - The BCCER is the Big Chico Creek Ecological Reserve off of HWY 32 between the Cities of Chico and Forest Ranch. This is the property where we do most of fall monitoring. The property is nearly 4,000 acres of mixed pine/oak forest, blue oak woodlands and riparian habitat along Big Chico Creek. Find out more about the Reserve here.

Migration Monitoring on the BCCER
When I came to Chico to attend Chico State in 2005, I was introduced to the BCCER. As a biologist and bird bander I am always curious about what bird species inhabit which habitats. Northern California had some similarities to Seattle and the Pacific Northwest, where I had come from, but it was a new ecological playground for me! I wanted to know if the NSWO used the BCCER habitats in the fall and winter. So with the permission from the BCCER director, I started a fall migration station in 2005. Since then we (me and a dedicated group of volunteer owl enthusiasts) have learned a lot about the NSWO population in this area. The first questions though were, do the owls migrate through the Reserve, and when does that occur? In 2005 during our pilot attempt, we found out that indeed they do migrate through the area and that this occurs between October and November. Take a look at these graphs and you can see when we get most of our captures, which varies each season. But let's start from the very beginning, and build the story from there.

Where it all started (the BIG picture) Project Owlnet
Project Owlnet, literally a network of owl migration monitoring stations, was established to improve the knowledge of Northern Saw-whet Owl (NSWO, Aegolius acadicus) migration in North America. In the beginning, starting with only five banding stations in the east, Project Owlnet encouraged other researchers to monitor the fall movements of the NSWO, and now there are more than 100 migration stations on the map (see below)! Because of these efforts we know that an amazing migration of saw-whets occurs each fall across the nation. Cooperating stations have determined the timing of migration, movement patterns and distances, and documented annual fluctuations in demographics (numbers, age and sex of birds) annually and over time.

Project Owlnet has three primary goals:

  • Support expansion of a network of migrant owl banding stations
  • Advocate the use of relatively comparable netting protocols
  • Improve communication and coordination between owl banding stations in the North America

Fall Monitoring Protocol at the BCCER

The first step is to find a location where you think NSWO might inhabit.  They are well known to use higher elevation, mixed deciduous and conifer forests for breeding. During migration the owls may remain on territory or if food sources are depleted due to heavy snows or other reasons, the birds will fly downslope and/or south.  The BCCER provided likely habitat and we set our owl stations in these locations.  Here you can see our Banding Station OWL2, which consists of mist nets for capturing owls, an audiolure (boombox) to attract owls into the nets, and a processing station- the picnic table where, after removing owls from the nets, we take them to band, age, sex and release. OWL2 consists of 5 nets, 3 which are 12 meters long and 2 that are 18 meters long. All are 3 meters tall.  The look similar to volleyball nets but have fine mesh and 4 tiers or shelves. The nets are set up each night of banding at sunset for four hours.  We turn on the boombox, which broadcasts the primary song or call of the male NSWO.  This is a consistent toot, toot, toot.  Birds are attracted to the call even during migration, and fly into the mist nets.  
Raina King is removing an owl from a mist net

 We check nets every 1/2 hour, remove the birds from the nets, place them into soft cloth bags and then bring them back to the table where we have our banding and measuring equipment.

Here is our banding table, with our data sheets and equipment used. We use banding pliers to apply the bands (size 4 for NSWO), wing ruler to measure the wing, calipers to measure the beak, a scale and container to weigh the owls, and a fluorescent ultraviolet (UV) bulb to help us age the bird.


The federal bands are called "butt end" bands. They fit over a peg on the banding pliers, then the pliers are opened, which opens the band at the seam between the butt-ends.  The band is then inserted into a hole in the banding pliers, placed on the leg of the bird and then closed, so the ends butt together, creating a tight seam.  The band fits like a bracelet, not too tight and not too loose, but enough to spin freely and allow for feather growth underneath. Click on the band image and you will see that the bands are stamped with a unique number.  Since most NSWO all over the country look similar in our eyes, banding them is our way of identifying them as individual birds. When a bird is recovered- either by recapture, injury or mortality, the band should be reported to the Bird Banding Laboratory (BBL).   The person reporting the band will receive a Certificate of Appreciation with the known information about that individual such as its age and sex, who banded the bird and when and where it was banded!

Banding the NSWO using banding pliers. The bander
is holding the owl in an owl- safe "banders grip"
Ageing and Sexing the Saw-whet 

Once we band the bird we want to know how old it is and what sex it is as part of our seasonal demographic study. By looking at age, we can determine if the owls have had a good reproductive year- expressed in the numbers of hatch year birds (under 1 year old)  that we catch. We look determine age by looking at the wing feathers or remiges of the owl. A hatch year birds feathers will be all the same age because they grew in the nest at the same time, so their feathers are uniform.  But an adult bird will have retained some old feathers and replaced some new feathers. Their wings show a "molt limit", the boundary between new and old feathers. Look at the obvious color contrast between feathers. The darker glossier feathers are newer than the browner, dull, more worn feathers.  This bird has at least three generations of feathers so is at least 3 years old!  We record the feather generations on our data sheets and then we confirm our findings using a really cool trick- a UV light.

In the very center of this photo you can see a molt limit between the 1st secondary feather (glossier and dark) and the older, browner 1st primary feather.

Below you can see that some feathers are pinker than others. Just as above, the newer feathers glow brighter pink.  All of the NSWO feathers have a pigment called porphyrins.  This pigment fades in the older feathers.  The bird below is 2 years old, showing two generations of feathers, with the newer, replaced feathers glowing bright pink and the older ones fading near the trailing edge of the feathers. 

In many raptors, the females are larger than males. This is true for the Saw-whet owl.  Females will have a longer wing and weigh more.  To sex the bird we measure the wing chord and take the mass of the bird. 

This bird had a mass of 90 grams and a long wing chord:
a female NSWO

In the picture you can see that the male is on the right and the female, who is larger, is on the left.


If we are not installing telemetry, we will take the bird to a tree or perch it on our arm, and release the owl. We send it off with new "bling" (a federal bird band), good wishes for safe travels, and a hope to see it next migration season.

Adios!  Released owl photo taken by Mike Fisher