WPBO Owls Fall 2010

Saturday, November 22, 2008

Lighthouse in the Snow

Lakeshore Ice

Winter has blanketed the Point! Snow fell most of this week so it was the perfect opportunity to tackle the season's data crunching. The most outstanding statistic that emerged is simply how scarce the owls were this fall. We banded 46 Northern Saw-whets, 24 Boreals, and 4 Barred Owls. Given that a lucky birder will find a couple Saw-whet Owls per year, 46 may sound like a lot, but this represents the fewest number banded during the past seven standardized seasons, the lowest percentage of young vs. adult Saw-whets, and the lowest overall capture rate. All-in-all, we caught 1 owl of any species for every 4 hours of operation. As many factors are always at play in nature, it's not possible to name the exact cause of these record lows, but it's hard not to guess that poor breeding success for Saw-whet Owls this year played a significant role in these outcomes. This speculation is further supported by the low number of juvenile Saw-whets recorded at the point during Chris and Nova's summer project.

Last Boreal Owl of 2008

The presence of Boreal Owls also made for an interesting season. With 24 individuals banded, this year may not qualify as an irruption, but more Boreals were present this fall than usual. Monitoring the cyclic nature of Boreal Owl migration in Michigan is a fascinating aspect of owl study at Whitefish Point. The graph below shows the number of Boreals banded during each fall from 1991 through 2008 (click chart to enlarge).

It has definitely been a memorable season for us, with the undisputed highlight coming after the official end date had passed. It has become apparent that this winter will be a great one for the chance to observe Snowy Owls! If you've been following the sightings blog, you know that SIX have been recorded at the tip since late October. If you haven't yet heard through the grapevine, one of them was also captured and banded by Chris!! It's been MANY years since this species was banded at WPBO (perhaps just the second one ever) and we feel extremely lucky to have witnessed it.

Keith holds his first Snowy Owl

Well, this wraps up the owl blog for the season - its been fun! We'd like to say thanks very much to WPBO for having us back for yet another year, thanks to everyone reading and commenting on our blog, and special thanks to our supporters including WPBO members and everyone participating in the 'sponsor a raptor' and 'sponsor a day' programs.
http://www.wpbo.org/Raptorsponsor.html
http://www.wpbo.org/Daysponsor.html

Good Winter Owling!
~ Keith & Wendy

2 comments:

ivars krafts said...: Beautiful pictures! Keep up the good work!!; November 22, 2008 at 9:14 PM
Marc Snyder said...: Excellent season summary - see you next year!; December 11, 2008 at 2:52 PM

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Our New Summer Owl Study

During the summer of 2006 WPBO conducted an exploratory owl banding research project at the Point. Our project ran 3 weeks, and our efforts resulted in the capture of 208 owls; 206 Northern Saw-whet Owls (NSWO) and 2 Long-eared Owls. Of the 206 NSWO captured, 200 were juvenile birds. While the spring and fall migrations of NSWO have become increasingly well studied across the continent, these results represent the first documentation of a significant concentration of juvenile NSWO during the post-breeding period.

Thanks in large part to generous donations made by two individuals and pledges to the spring staff birdathon, we have been able to continue and expand this study during the summer of 2007. We began on July 1st, and as of August 10th we have banded 542 owls; 539 NSWO and 3 Long-eared Owls. As in 2006, the majority of the NSWO we have banded this summer have been juveniles.

In addition to the regular data we collect on all owls, we are visually accessing fat stores and muscle mass on all of the juveniles. Among North American owls only NSWO and Boreal Owls have a juvenile plumage that is significantly different from adult plumage. The juveniles begin actively molting out of their juvenile plumage and into adult plumage during our study period. Detailed descriptions of the molt progression on each juvenile have been collected.

Owl banding Spring 2007

Several changes were made to the spring owl banding protocol in 2007. These changes were made in an effort to increase our captures, thereby increasing our data base and our knowledge of the owl migration at Whitefish Point. Owl banding data collected by WPBO during previous springs clearly demonstrated that the Saw-whet migration at Whitefish Point was already at its peak during the 1st week of April. Therefore, the start date of the spring owl research was moved up from the previous start date of April 1st to March 15th. Audiolure was also introduced to the spring owl research for the first time. Audiolure is simply the practice of broadcasting a recording of an owl's call to lure them into the research area. This is a technique implemented at every other owl migration banding site that we know of, and has been used during the fall season at Whitefish Point since the fall study began in 1993. It has been documented that this practice increases Saw-whet captures 5-10 fold.
This spring the calls of Northern Saw-whet and Boreal Owls were broadcast. As the data from previous seasons suggested would be the case, Boreals were at the bottom of their irruptive cycle and none were captured. We fully expect that Boreal Owl captures during the next irruption will increase significantly due to the use of audiolure. As for Saw-whets, the changes proved a huge success after just one season. We banded nearly 280 Saw-whets during March alone; the previous high for an entire spring season was 122. Our total captures for all owl species in March was 318, these results are also higher than the total captures of any previous spring season. The chart below demonstrates the effectiveness of the changes implemented in the spring of 2007.

General Information

Whitefish Point Bird Observatory (WPBO) conducts long-term owl migration studies in both spring and fall. WPBO began its oversight of the spring owl research at Whitefish Point (WP) in 1988, and began the fall study in 1993. A summer study was developed during the summer of 2006 when a dispersal of juvenile Northern Saw-whet Owls was discovered within the study area. These WPBO research projects have resulted in the banding of over 7,000 owls of eight species; Great Horned, Northern Hawk, Barred, Great Gray, Long-eared, Short-eared, Boreal, and Northern Saw-whet. This reasearch has established WP as one of the most diverse owl migration sites on the continent.

* Study periods:
Spring: March 15-May 31
Summer: currently July 1-August 31
Fall: September 15- October 31

**During the study periods nets are opened nightly, weather permitting , 1/2 hour after sunset and closed 1/2 hour before sunrise. Nets are not opened during periods of rain or high winds.

FAQs

Why do we band owls?
The owl banding project is the most effective way we have to monitor the number of owls migrating through Whitefish Point. For example, without the owl banding project just 3 Saw-whet Owls would have be documented in the spring of 2007. Through the owl banding project, 750 Saw-whets were banded and 32 that were already banded were caught. Without specific efforts to document the owl migration at Whitefish Point it would go virtually undetected. For more information on bird banding visit the Bird Banding Lab's website, which can be linked out of the WPBO website.

How do we catch and handle the owls?
All of the owls in our studies are captured in mist nets that are made specifically for bird banding. The mist nets we use are 12 meters long andabout 10 feet high. Due to the size difference between species that we catch two different mesh sizes are used. The nets are placed in openings among the trees at Whitefish Point. To help attract the owls into the netlanes audiolure is used. Audiolure is simply the broadcast of an owls call.In spring and fall both Saw-whet and Boreal Owl calls are broadcast, only saw-whet calls are broadcast in the summer. We do not wear gloves while getting extracting owls from the nets or during the banding and measuring proccess. Like many other things, these procedures are more difficult when wearing gloves. Extractions in particular are already difficult and would be virtually impossible while wearing heavy gloves. Yes, we do occasionally get bit or have the birds get us with their talons, and yes it does hurt. To band and weigh the owls they are placed in cans. This is the common practice when banding birds of prey and actually serves to calm the birds down.

What data do we collect?
Each owl is fitted with an individually numbered U.S. Geological Survey band. These bands are issued to federally licensed bird banders by the Bird Banding Lab in Maryland. The main measurments we collect are weight, tail and wing chord length. If the bird has flight feather molt, the molt pattern is recorded. These measurements and the molt patterns help us determine the age and sex of many of the owls that are captured. The data, including the band number is then submitted to the Bird Banding Lab for inclusion in their database.

Saturday, November 22, 2008

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