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.

2006

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)

2007

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)

2008

2/19/2008 (1 at BCEP)

2009

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)

2010

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)

2011

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)