By getting rid of the larvae infestation in the lawn - that's the most likely explanation, either leatherjackets or chafer grubs. The birds peck at the lawn to get the grubs out. Lay a sheet of plastic on the grass somewhere overnight, lift it early in the morning - you should see larvae on top of the soil if its leatherjackets.

I like watching the jackdaws, but I won't advise leaving the chafer grubs! The birds are often the first indication that something's amiss. Been a common problem over the last year or so, and chafers tend to proliferate on a four year cycle, so with any luck our lawns will be better next year.