Friday, 27 November 2015

Landfill gulling: the end is nigh?

Gulls have a visible, year-round presence in London, just as they do in many other places, but things are changing. Life is not what it used to be for larids on the capital's landfills, even compared to just a few years ago, and the same must be true on many other tips in south-east England and beyond. Waste management policies have changed dynamically, and all of a sudden far less food waste is being disposed of alongside general refuse - our left-overs are, of course, the reason why gulls and other birds (typically corvids and Starlings) scavenge on landfills.

My study site four years ago - upwards of 10,000 gulls were present on several occasions.
So what's happening? Increasingly, food waste is now being composted by local authorites, reducing the amount of money they pay in Landfill Tax, freeing up space for other waste in landfill and providing a new revenue stream in the process. According to government figures published a year ago, the amount of food waste sent for composting (including anaerobic digestion) has more than doubled since 2010. And overall, local authority managed waste going to landfill has fallen by 60 per cent since 2000/01, and is down by 6.8 per cent compared to 2013/14. In 2000/01, the majority (79 per cent) of all local authority waste was sent to landfill; this has continued to decline and the proportion sent to landfill was just 31 per cent in 2013/14.

The ability to study gulls at close range on landfills has helped refine the ID criteria for species such as Caspian Gull.
That may be a good thing environmentally, as organic material such as rotting food and garden waste disposed of in landfill is broken down by bacteria and ultimately generates methane, a greenhouse gas shown to have a warming potential 21 times greater than that of carbon dioxide. But a direct result is that gull numbers have fallen dramatically, being able to exploit only a small proportion of the food waste formerly available.

Landfill ringing schemes and colour-ring reporting have also improved knowledge of gull dispersal and migration. This first-winter intermedius Lesser Black-backed Gull was ringed as a chick in a colony in north-east Denmark
and resighted on its first southward migration in east London, probably en route to Spain or north-west Africa.
In time the impact of this change may be felt in breeding populations as well as by feeding birds. Although an analysis of Lesser Black-backed Gull data shows that birds breeding in urban areas are currently more productive than their rural counterparts, common sense suggests that this must change as landfills become largely dry waste burial pits. Worryingly, a recent study in the Balearic Islands found that after the landfill closure there was a significant decline among local Yellow-legged Gulls in the average body mass of breeding females and males, in average egg volume, and also a shift in the modal clutch size from three to two eggs. Rotting food waste may be low in nutrients, but it is still food.

Landfill throngs like this in south-east England are fast becoming a thing of the past.
While rising human populations and their trash mountains may have helped fuel an expansion in gull numbers and distribution in recent decades, today's more efficient recycling and disposal techniques are putting that trend into reverse. I haven't been counting gulls at my study site for long enough to have any meaningful long-term data on this, but anecdotally, in winter 2010-11 I estimated upwards of 10,000-15,000 birds in total on several occasions; today, I counted 838 large gulls of five species, and 78 per cent of them were European Herring Gulls. This species may be ubiquitous in Britain and the 'default' large gull, but it is also on the Red List of Birds of Conservation Concern. The Amber List is even more heavily populated with larids, and Great Black-backed, Lesser Black-backed, Yellow-legged, Glaucous and Iceland feature alongside Mediterranean, Little, Black-headed and Common. With the decline of Britain's fishing industry preceding that of its landfills, is it any wonder that gulls face an uncertain future?

With little food waste being deposited in landfills, the environment may benefit but gulls will not.


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