Sand Martin mid season report

In recent years I've blogged a lot about Sand Martins after each session or each week.  As the pattern of catching is pretty similar with early visits being mostly adults, mid season visits being a mix of adults and juveniles and late visits being mostly juveniles it all becomes pretty similar and I may as well say 'read previous year's report for these dates'.

This year has been vastly more successful than last year due to better weather and consequently river levels that are not over topping banks or flooding out burrows.  As a result we have:

- More captures for 2013 than we managed in all of 2012 although with increased effort in 2013
- 50% of the captures by this point in the season than we had in 2010 and 2011 with similar effort.

These figures reflect how poor 2012 was and how late the 2013 season is (about 10 days later for Sand Martins).  2010 and 2011 were exceptional in terms of productivity and occurred on top of good winters for returning birds.  2012 on the other hand had poor survival from the 2011 winter and a poor breeding season which has led to a lower population in the Lune valley.

As this is part of the BTO's Retrapping Adults for Survival programme (RAS) we are aiming to retrap birds from previous seasons to understand the survival of Sand Martins between years.  So far this year we have visited 3 large colonies and not managed to get into some smaller colonies due to windy weather limiting evenings we can ring on.  The retrap numbers from previous years are below:

Year of Ringing	Juvenile	Adult	Juv return rate	Adult Return rate
2009	0	1	N/A	0.5%
2010	2	0	N/A	0.1%*
2011	7	8	N/A	1%
2012	9	19	5%	13%

* Return rate calculated from total number of adults handled in each year and proportion caught this year.  As few adults were ringed in 2009 a higher proportion have survived than from 2010.

Following a good winter we typically expect 20% of adults to return and roughly 15% of juveniles although this varies from 2% to about 20% depending on various factors.  The 2010/11 winter gave us a return rate for adults of about 8% and the 2012/13 winter has given us a 13% return rate for adults.  As we caught about 1200 individual adults in 2011 we would expect (given the above rates) to retrap roughly 13 birds caught as adults in 2011.

Totals ringed so far this year are:
New Adults - 266
New Juveniles - 228
Retraps from previous years - 46
Controls - 1 UK ringed, 3 French ringed.

While nice to catch the foreigners it is hardly surprising given nearly every British Sand Martin will migrate through France on the way to winter in Africa.

Richard