Where are the birdies?

16 Mar 2014

As soon as spring gathers pace the trite rhyme ‘spring has sprung, the grass is ris, I wonders where the birdies is?’ comes into my mind (much to the annoyance of our middle daughter Emily). This year it has more relevance because the numbers of birds in our central Cambridge garden are the lowest I can remember. This is an unexpected observation after such a warm winter when there was plenty of bird food available. The berries in the garden are almost untouched.

The numbers have been falling for years whilst the numbers of magpies and hawks have increased. There is a history of bird egg shells on the lawn and I’ve witnessed hawks hunting. However, the number of magpies has fallen locally over the last couple of years, possibly because they were running out of victims’ nests and have gone elsewhere.

I am not alone with these observations and neighbours are questioning why they are feeding birds. This raises the possibility that success in encouraging bird numbers should be measured not by their numbers but by the prevalence of their enemies, such as magpies and hawks. On this basis, the measures that have been taken to increase birds locally over the last few decades have been a great success!

On farms there are additional hazards for ground nesting birds; these include badgers. They commonly hoover up eggs and chicks in the areas established to provide habitat for ground-nesting birds and in nearby skylark plots in crops. We all know in which direction badger numbers are going.

However, I do recognise that changes in arable agriculture, which have resulted in a dramatic increase in food production, have contributed to the fall in farmland birds. One generally recognised reason was the switch from spring to winter cropping in the 1970s and 1980s. Spring cereals provided a habitat for some farmland birds and the weeds in the crop were a source of food, either as hosts to insects and/or as seed.

The trend in some areas is now towards more spring cropping because of black-grass resistance to herbicides.  So, logically, should this be good for farmland birds? It may be helpful but the management of spring cereals is not what it was forty years ago.

In the 1960s and 1970s, the land was ploughed for spring barley after the winter cereals were sown in mid-October.   It was a steady winter job. The stubbles being ploughed also had recently shed crop and weed seeds on the soil surface. So birds like the skylark had large areas to rest in and had a food source away from field edges. This is no longer true with the land being prepared for spring cereals earlier in the autumn, when soil conditions are generally drier, and improved harvesting techniques and cleaner crops meaning that there is less crop and weed seed around.

In addition, spring cereals are now sown a lot earlier, as soon as conditions are suitable after mid-November, and higher seed rates are used where there is a requirement to compete with black-grass. Generally more nitrogen is now being applied although some heavy-land farmers have been adopting modest doses in order to produce malting quality spring barley. This all means that the relatively open spring cereal crops, suitable habitats for the later clutches of skylarks, are now less likely to occur. In addition, the standard of weed control is now higher than it was a few decades ago. Some annual broad-leaved weed species that tend to emerge in the spring are particularly beneficial to farmland birds, e.g. knotgrass and fat hen. However, in situations where spring cereals are being adopted because of black-grass, the soil seed bank will be largely devoid of these species after many years of winter cropping.

This all suggests that spring cereals will not provide the habitat and food for birds that were provided in the 1960s and 1970s. However, it may be that I am being unduly pessimistic.

There are a number of other trite rhymes that come into my head on occasions (no comments please!). One is ‘the bleedin’ sparrer’ which was obviously written in the days when sparrow hawks were controlled. Sparrow numbers have fallen dramatically over the last few years, probably due to a number of reasons including more predation, less hay-fed livestock and excluding birds from agricultural buildings. There was one statistician who even found a relationship between the increasing adoption of lead-free petrol and the decreasing number of sparrows. I have commented many times about scientists putting lines through charts and then believing the line represents the truth; this must be a prime example where great care is needed in the interpretation.