Thursday, March 31, 2011

Spring Migration- what do the years tell?

Just recently we completed our NSWO spring sampling and ended up with a California Bat and no owls.
Most every year we - the owl team - make some efforts to determine when the N. Saw-whet Owl spring migration occurs in our area. We have nailed down the fall migration which occurs between Oct 1 and Nov 30, and peaks at the end of Oct, beginning of November. We also know that birds winter at the Reserves based on recaptures in winter months and telemetry locations in 2011. I would consider any February birds that we captured as wintering birds, with some possible movement at the end of February.

Over the years it appears that the birds move between the first and last week of March. 2009 was odd as we had a March 4 capture (could have been wintering) and an April 4th capture (our latest season capture). Using Steve's technology (a remote broadcaster and recorder) we have documented our latest detection on April 21, 2011!

Here are the data. Please note all of the 0 detection/capture nights and think about how dedicated my volunteers are to continue through the years.

1/6/2006 (3 [2 and 1 recap] at BCCER)
2/7/2006 (3 [1 and 2 recaps] at BCCER)
2/22/2006 (0 at forest ranch)
3/7/2006 (2 at BCCER)
3/20/2006 (detections but no captures)
4/21/2006 (0 at BCCER)
4/28/2006 (0 detections/captures at BCCER)
4/30/2006 (0 detections at BCCER)
5/7/2006 (0 detections Magalia @2600')
5/12/2006 (0 detections forest ranch @3000')
5/16/2006 (0 detections at BCCER)
5/17/2006 (0 detections at Magalia)

1/21/2007 (2 [1 recap at BCCER)
3/1/2007 (0 at BCCER)
3/10/2007 (4 at BCEP)
3/16/2007 (0 at BCEP)

2/19/2008 (1 at BCEP)

1/22/2009 (1 at BCEP)
2/28/2009 (0 BCCER)
3/6/2009 (1 at BCEP)
3/20/2009 (o captures but NSWO detection at BCCER)
3/23/2009 (3 at BCCER)
3/25/2009 (3 at BCCER)

1/8/2010 (2 at BCEP)
1/8/2010 (3 [2 new plus 1 recap] at BCCER)
1/31/2010 (0 at BCCER)
2/18/2010 (0 at BCCER)
2/25/2010 (0 at BCCER)
3/4/2010 (1 at BCCER)
3/11/2010 (0 at BCCER)
3/13/2010 (0 at BCCER)
3/25/2010 (0 at BCCER)
4/4/2010 (1 at BCCER)
4/7/2010 (0 at BCCER)
4/21/2010 (0 at BCCER)
4/30/2010 (0 captures/detections)

2/10/ 2011 (2 [1 new and 1 recap at BCEP)
3/7/ 2011 (3 [1 new and 2 recaps at BCCER)
3/29/2011 (no detections or captures at BCEP)
3/30/2011 (no detections or captures at BCCER)
4/12/2011 (bird tooting-heard on Steve's remote recorder)
recordings in between April 12 and April 21 accidentally deleted by me
4/21/2011 (bird wailing- heard on Steve's remote recorder)

Wednesday, March 9, 2011

Winter Sampling at BCCER - March 7, 2011

On this winter night we set up our station at OWL3 at the BCCER. Past years have suggested that spring migration to the summering grounds occurs in early March when we have captured several owls in one setting. On this night serenaded by a great horned owl and numerous flocks of snow geese flying overhead, we captured three owls, but only one of these was unbanded. The other two owls had been captured three times previously, making this their fourth capture, an uncommon event. Our recapture rate is low and this is attributed to the birds being "net savvy;" once a bird is captured they rarely go back to the same site during the same season. These two owls seem to be "net happy," due to the high number of times they have been captured in the same season. It tells me that the audiolure is extremely attractive to some owls!

Here is their story.

Both birds were banded on October 15, 2010 during fall migration at the OWL3 site at BCCER. They are identified as band number 1014-14523 and 1014-14524, and although their band numbers are sequential, they were banded at different times that night. Each was captured on different nights two more times until March 7, 2011, when they were captured together again- this time during the same net run time. The number of days between capture is 149 days -close to 5 months, which is great evidence that the BCCER provides fine wintering habitat for these owls. Other research has suggested that siblings may travel together during migration, and although we can't say for sure, these birds could be siblings, based on the their capture patterns, see below.

Capture Date / Mass in grams / Sex (based on wing chord length and mass)
10/15/2010 84.3 unknown
11/1/2010 98.9 female
1/27/2011 84.9 unknown
3/07/ 2011 86.9 unknown

10/15/2010 95.4 female
10/16/2010 90.4 female
11/3/2010 97.2 female
3/07/ 201 93 female