Friday, November 3, 2017


Yep, that's how many owls we have banded since our first night of owls on October 12, with an opening night of 13 owls! Now on November 3rd, we still have a couple of weeks of migration (October 15-November 15, with sampling on either end). It is our highest number of migrating owls since we have run the station annually in 2005. VERY exciting! The majority >80% have been Hatch Year (HY) owls, hatched sometime this summer in 2017. All these youngsters are easy to age. Here's how. We look at the dorsal side of their wings to see what their molt pattern looks like. And we use descriptions like chocolate to describe the color differences between new and old feathers. We look at the remiges; the primaries (10) and secondaries (13).
Hatch Year, all feathers one age (uniform molt pattern)

Second Year, outer primaries and inner (closest to body) secondaries have been replaced,the new feathers are darker(dark chocolate) and of higher quality then the old,
retained (milk chocolate) feathers. 

After Second Year, (over 2 years old) has three generations of feathers
fresh (dark chocolate), old (milk chocolate) and very old (old milk chocolate!)
And then, there is the magic trick to confirm our age determination. We look at the ventral wing and turn on a black light and like a black light poster, the feathers glow! It's actually a pigment called porphyrin. If you like chemistry, go here to learn more about porphyrins.

Notice the difference in porphyrin glow? As the feather ages, the pigment ages too;
the older feathers don't glow as brightly as the fresh feathers. How old is this bird?

Friday, October 20, 2017


The wolf spider! Volunteer Mary Muchowski found this lady on our way down to check the nets. Guest Dan Roskopf was with us to meet a NSWO, and took the spider's photo. She's a protective mother, carrying tens of babies on her back. Apparently this is rare spider behavior, only wolf spiders do it, so I feel very excited that we got to see her! Watch this video to see a live version of active young wolf spiders: 

Wolf spider mother and hitch-hiking babies, Dan's photo
there is always something interesting in the night.... Come join us and see for yourself!
Dan and Mary with NSWO, Dan's first!


Owl season was off and running on October 13, 2017 when program directors Ken and Julie and volunteer Mary, banded a whopping 13 owls!! Since then, we have been out six more nights and have banded 5, 5, 2, 7 and 6 owls, = 38 owls, averaging 6 owls a night. A great surprise, we had one recapture from our Snow Goose Festival event from January 2017, showing migration site fidelity. Recapture information is always valuable.
  • NSWO profile. They are amazing tiny predators, and captivate all that meet them!

Lucky guests, meet and release a NSWO

Volunteer Carol Anderson with saw-whet owl.
Volunteers help drive our program, thank you!

All our other owls are new owls without bands and most are hatch year birds, meaning owls were hatched in summer 2017, and it was a great summer for saw-whet owl breeding! We have also captured and released 3 pallid bats, a flying squirrel and a katydid!

Sunday, June 11, 2017

OWLETS In a Box and Another Occupant

Ken was able to check the owlet box this week; the chicks look healthy and mom is still roosting in the box with them. Both owlets are losing their down feathers and looking more and more like adults as their contour feathers grow. They were more curious about the camera then mom, who has the adult wisdom to avoid predators, lie flat and be still.

This owlet in the box is still pretty downy.
This owlet is slightly older, showing more contour feathers

The nestling phase is about 35 days so they should fledge between the 3rd week and end of June. We were hoping to put up some cameras around the nest box to watch the parents deliver food and the chicks fledge, but the supporting trees were too far away. We'll have to come up with other ideas.

Meanwhile, last week we found another occupant in nest box #2. We have deduced, based on the list of cavity nesting birds in the area, that it was an ash-throated flycatcher egg. Since there was only one egg and it had ants on it, we determined it was abandoned. This weeks' box check confirmed it, no new eggs, more ants.  Here's how Cornell Lab of Ornithology describes the egg, "creamy white with reddish brown streaks and elongated blotches." Click this link for more information about the ash-throated flycatcher. 

Monday, June 5, 2017

Western Screech OWLET UPDATE and Photo Essay!

#1! Lots of down but some contour feathers appearing
#2 of the two owlets
It was time to band the owlets after peeking into the box last week, I determined they were old enough, ~ 3 weeks to 1 month old and getting ready to "fledge." Typically owls leave the nest cavity and are called "branchers", because that's what they do, sometimes falling clumsily to the ground, climb up a tree, and perch on a branch. Their growing flight feathers are heavy with blood and they beg for food and begin to persistently follow their parents around before they are capable of even moderate flight. I wondered about this being a successful strategy because it seems safer remaining in a protected cavity. But after seeing and smelling the remains of this nest box, I think I figured out why it's best to get out of there (see below!)
At least 3 prey remains in this nestbox
Here is more evidence of the male being a good provider with three different prey remains that might be a deer mouse, vole or gopher and the tiny remains of a pocket mouse or other tiny rodent.

Ken climbs the ladder and hands me the mom for
weighing and checking the band we put on last week.
You can see the plug in the nest hole.
We begin with Ken removing the female from the box (the nest hole is plugged to ensure she doesn't flush out of the nest) and handing her to me. She is held in a bag until the nestlings are banded. As typical for screech owls, she is very calm through this process.The female has a lot invested with two owlets, so would unlikely abandon a nest at this stage. Both owlets were plump at 135-145 grams (the same weight as some adult males).  We banded and weighed them separately, so owlet #1 remained in the bag quietly waiting for the sibling.The mom was also well-fed, weighing in at 190 grams!
One owlet banded and held in a cloth bag until the second owlet is processed
The owlets are returned to the nest box, then mom is returned. We wait about five minutes to remove the plug before leaving the owls safely in their box. I have no doubt the male is roosting somewhere nearby, but we were unable to find him.

Saturday, May 27, 2017


Today Ken and I checked the boxes on the Reserve. We were particularly interested in Nest Box #15 (sort of like an address) where we discovered a nesting Western Screech Owl, 37 days ago in April. Today May 27, we saw a mom owl with her two owlets and a nice meal for the chicks, a deer mouse (peromyscus sp.)

A view from above: 3 screech owls and breakfast. Note the larger owlet on the left.
Owl eggs hatch asynchronously, so one will be a little older than the next.
Ken removed the female and lowered her down to me for banding. She remained still and calm through the process.We returned her to the box after taking some measurements and examining her condition.
Here I am taking the wing chord measurement of the owl.
Note the band on her right leg.

Then I looked at her brood patch. Hormones help release breast feathers providing direct heat exchange for incubating eggs and brooding young,until owlets can thermoregulate on their own. This female's brood patch is already getting pin feathers (two dark lines under her bare skin), because the owlet's feathers now keep them warm. By fall her breast will be feathered, which will help keep her warm for the winter months.

The brood patch, well past its use for warming chicks. Because the
chicks now have feathers they no longer need warming by the adult.
Leftover prey shows the male is a good provider. He was likely roosting in a cavity nearby, and maybe observing us. Stay tuned for the rest of the story!
A view with the mom removed. The owlets are about the size
of an adult deer mouse (right corner), and too small to band.
The Cornell Lab of ornithology is a great resource for bird natural history including screech owls. Also click here for a nice overview of owl courtship and reproductive behavior.

Friday, April 21, 2017


Western Screech Owl inside a nest box
Can you see the the owl in the box?  You are looking at the head and back of a Western Screech Owl inside nest box # 15. We believe she is incubating eggs due to her flattened posture and absolute stillness when we peeked the camera into the box. If she is incubating and all goes well, we can expect to see 2-7 nestlings within the next month.

So how did we see her? This winter Ken and crew installed nest boxes to determine potential use of the BCCER as breeding site for Northern Saw-whet owls, a cavity nesting species. To check the nests Ken attached a flexible cable with tiny camera and LED light to a bamboo pole, plugged in to his tablet. He can feed the camera quietly into the cavity entrance, see what is inside on his screen and then take a photo. We have conducted two box checks,

Ken's nest-cam set up. The camera is at the end of the pole
inside box #4. He is viewing the inside of the box on his tablet.

one on March 11 and one on April 19. In March, we found bird feces in two two boxes but no birds were present. We guessed the boxes were used by Northern Flickers roosting in the boxes at night. In April, we found identifying flicker feathers in the same boxes, and then we found the screech owl in a third box, What a fun surprise! Learn more about Western Screech Owls here.

Monday, March 6, 2017

SPRING MIGRATION, what do we know?

As with many of our questions, the answer is.....more study is needed! According to Project Owlnet, spring migration is poorly studied. And so, Ken and the owl monitoring team are making winter/spring efforts more standardized to identify migration timing on the Reserve. So far this year we have seen some new activity near the end of February with 10 new owls so far! Here's what it looks like:
February 25, 2 new owls
February 27, 5 new owls and 1 recap
February 28, 1 recap
March 2, 3 new owls
March 3, 0 owls
Bander Erika Iacona with one of the February 27 owls.
Is this a sign of spring migration? Possible, BUT, this year has been unusual, relative to the past 5 drought years. We have had record rainfalls and snow levels in the Sierra, which may hinder birds from moving to their breeding sites too early.So, we will continue our spring efforts to  enlighten our migration question this year. WAIT FOR IT!

Thursday, February 16, 2017


We know based on aural and/or visual detections that we have at least five species of owls on the Reserve; great horned owl, Northern pygmy owl, Northern saw-whet owl (NSWO, fall through spring?), California spotted owl (winter only), and Western screech owl (WESO). The screech owls are year-round residents and will sometimes come to investigate our NSWO caller, so they get caught in the nets. We have banded 25 WESO over 12 years of monitoring NSWO. Sometimes we are lucky to see them roosting in a cavity during the day, or perching at night. Banders Erika and Ken saw this owl perching in the barn, likely
Western screech owl in the barn at the Reserve
Possibly foraging on bats? He/she appears a little
perturbed at the disruption!
taking advantage of barn mammals. It may have been foraging on the bats that roost there! There happens to be a colony of wintering free-tailed bats, and potentially other bat species, living in the barn. I have seen great horned owls, peregrines, merlins, kestrels and red-tailed hawks capturing bats as they exit their roosts. It was quite an exciting flight dynamic as the predator bursts in a cloud of bats.  The success rate on capturing bats seemed pretty low. What we need to determine if this WESO has a palate for bats, is to find some pellets to identify prey remains.

Wednesday, February 15, 2017

A Winter Owl's Meal

Ken and team have continued monitoring owls through the winter and have found that three individuals have remained on site since fall. Three others were newly banded this winter and recaptured. It appears the wintering population of saw-whets on the Reserve is pretty good-which indicates that the prey base it sound. And proof is in the owl mass- all have increased since their first banding. Below is an example of this female's weight history, captured and weighed three times.
one wintering NSWO captured and weighed 3 times
01Jan2017 =  90.5 gr
02Feb2017 =  95.6 gr
11Feb2017 = 101.7 gr

NSWO are primarily rodent predators, but are also opportunistic, taking advantage of what's available (birds, insects, etc).From previous pellet analysis conducted by Julie Shaw (see earlier posts in 2010-2013) and visual observations we know Reserve owls eat field mice, deer mice and California voles. One owl even ate rain beetles! Saw-whets will often make two meals out of one prey item and roost with it or cache it for the next meal.

A great web photo of a NSWO with deer mouse prey

Friday, January 27, 2017


In a fun competition, Ken Sobon and I bet on which banding site would band the most saw-whet owls for the 2017 Snow Goose Festival (SGF) field trips. The festival is a great opportunity to see if owls are wintering on site. SO, Ken and crew Julie Newman, Wyatt Hersey and Maureen Morales, and Reserve research director Jon Aull, took SGF participants up to the BCCER (our typical fall monitoring site). Banders Julie Woodruff, Erika Iacona  and I, set up nets at Butte Creek Ecological Preserve (BCEP), an alternate winter banding site. AND the winner was........
Ken Sobon bands a wintering  saw-whet owl at the BCCER 
Red light helps the owl adjust to the night sky where it will be released

SGF participant releases a saw-whet owl
BCCER-with 2 saw-whet owls! We had no saw-whet owls at BCEP- but Butte Creek was flowing high and very loud which may have had a impact on owls hearing our broadcast. Our night was enhanced by loads of stars and Ryan's (Reserve staff) fire. Guests were offered an opportunity to band owls this fall. At the end of the night when all was quiet, a western screech owl flew into our site and called for a half hour.

Friday, January 20, 2017

ATTENTION SAW-WHET OWLS - Nest Boxes Available!

Ken Sobon and team have installed over 15 nest boxes on the Big Chico Creek Ecological Reserve (BCCER). He is hoping that the boxes will attract saw-whets, perhaps those wintering on the Reserve or moving through in spring, will stay and nest. If a pair does-it would be the first documented saw-whets breeding on site! We haven't done any summer surveys so we can't say they don't breed here. Generally I think the Reserve is too low in elevation (and hot) for Sierra Nevada breeding habitat, but these owls are shown to be nomadic, meaning they will breed where conditions are right (good prey, micro-climate) and don't often return to the same breeding area.
Locations of seven nest boxes on the Reserve. Also see our two banding sites, OWL2 and OWL3. The structures include barn workshop, office and old ranch house.The forests provide cover and good roosting habitat for owls and the meadows are great habitat for foraging for rodents.
You can see the boxes are distributed around, mostly under good canopy cover and near meadows for foraging and all boxes face NE (cooler). Some are on different tree species, some near small drainages, some with a different slope aspect.  It will be really exciting to check these boxes. Other cavity nesters that might find the boxes homey are western screech owl, ash-throated flycatcher, northern flying squirrel, wood rats and???  Monitoring begins in early March. Stay tuned!
This box #8 will be under a fairly dense cavity when the oaks leaf out.
You can see the canopy closure in the aerial google earth photo above
taken in late May.

Wednesday, January 18, 2017

Let's Get it Started! Nest Box Program for the 2017 NSWO Breeding Season

New project co-director Ken Sobon is moving forward into the breeding season for owls. We don't know if NSWO breed on site, but we have captured them as late as 4 April, likely during spring migration. We have made limited attempts during the late spring, early summer to identify nesting birds, with negative results. BUT this species is opportunistic and considered to be nomadic, nesting where the prey base and other conditions are right, and not necessarily returning to the same nesting area. Habitats on the Reserve could be good for saw-owl breeding in some years.

Ken's nest box building team, hoping to entice saw-whet owls!

Drilling the "cavity" entrance
Ken and his team may be monitoring for years before
actually finding a breeding owl, or it could happen this spring. If he does find a saw-whet it will be the first documented nesting on site. He might also find other cavity nesters using the boxes including Western screech owl, American kestrel, ash-throated flycatcher, northern flying squirrels and ??? Check back to our blog!

Ken installing nest box #5

Tuesday, January 10, 2017

New Project Directors Ken Sobon and Julie Newman 2017

Welcome Ken and Julie as the Northern saw-whet owl fall monitoring project's new directors. What a great journey it has been and a privilege to pass the project along to these two dedicated volunteers. Ken is the VP for Altacal Audubon Society (our project sponsor) and Julie is a professional environmental scientist. Both have banded and participated with the project for several years.
Ken Sobon, NSWO project Co-director
Julie Newman, NSWO project Co-director

Long-term monitoring of a species is essential to understand population trends and local natural history. Thank you for continuing this important work. Great team!