Sparrow weather?

1st May 2012, Tuesday

I participate in nestbox challenge, a BTO initiative that encourages people to record the use of nestboxes, and the survival of eggs and chicks.  During this last month we had four house sparrow nests supporting  chicks for more than a week in late April. All of the nests contained young birds for at least 7 days and survival during this wet period was just 55%.

male house sparrow

At first this figure did not seem particularly high and I blamed

the wet weather for limiting the amount of invertebrate food, but looking at data for April 2011, a hot dry month, survival of chicks in 5 nests was even worse at only 50%, so perhaps the wet weather has not influenced hatchling survival? Or has it?

April 2011 was so warm that my family spent a lot of time in the garden, and this was inhibiting birds returning to the nest box with food.  So perhaps the mortality in the two years resulted from different factors causing chick starvation.  2011 was a slightly earlier nesting season with the first chicks fledged by 1st May.

In 2010 egg laying was late so there is no comparable data for April, but in 2009 we had 80% survival of chicks in April.  That year, however, there was only one nest so it is not fair to compare the two years.  Which brings me to the numbers of house sparrows.

Our population has increased from one nesting pair in 2009 to 4-5 pairs in 2011/12. An encouraging sign, matched by an increase in the numbers of birds counted feeding in the garden in my weekly garden bird counts between spring 2008 to the present day.

Weekly house sparrow counts 2008-2012

The number of birds fluctuates on a yearly cycle with the lowest counts at the start of the nesting season, and highest counts in the late summer/autumn.  The trend is clearly upwards with fewer low counts of less than 10 birds this winter, and more counts in excess of 30 birds last autumn.

I put this down to constant feeding of the birds with a good seed mix, provision of nest boxes, plenty of shrubs for roosting, and allowing the grass to grow longer than usual in the spring to provide invertebrate food.  Across the country house sparrows had a good year last year, with numbers of gardens supporting the species clearly up in the Garden Birdwatch scheme, for the first time after a number of years of sustained decline.  What will happen in 2012?