Chickens, Trees and Farmers - an Experiment in Mutual Benefit

By Marian Stamp Dawkins, Department of Zoology, University of Oxford - Unlike adult laying hens, broiler or meat chickens are juveniles and most of them are killed when they are less than six weeks old. People like to see them ranging outside and enjoying the fresh air so that it is decidedly disappointing if, when they are given access to an outside area, they then don't make much use of it, as sometimes happens.
calendar icon 14 March 2006
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Chickens, Trees and Farmers - an Experiment in Mutual Benefit - By Marian Stamp Dawkins, Department of Zoology, University of Oxford - Unlike adult laying hens, broiler or meat chickens are juveniles and most of them are killed when they are less than six weeks old. People like to see them ranging outside and enjoying the fresh air so that it is decidedly disappointing if, when they are given access to an outside area, they then don't make much use of it, as sometimes happens.
Department of Zoology, University of Oxford

But if chickens do not range as far as we would like them to, perhaps it is our fault for not providing an outside environment that is attractive enough to them. All our domestic breeds of chicken are descended from the Red Junglefowl - sometimes known as the Bamboo Fowl - of South East Asia. Junglefowl are essentially birds of the dry forest and are found in areas where there is plenty of undergrowth, such as bamboo thickets or along the edges of human settlements. If they do venture, cautiously, out into a clearing, they usually remain within easy reach of cover and can silently and quickly melt back into the undergrowth.

No wonder, then, that many farmers are beginning to realize the benefits of creating the ancestral home by providing their birds with tree cover. But what we don't know is whether this does actually improve the birds' welfare. Are they genuinely better off roaming in their forest or is it just satisfying our human idea of what chickens 'ought' to be doing? Are consumers really buying higher welfare or does it just look good on the label?

With the help of funding from Defra, we set up a unique experiment to find out. We call it unique because although many people had given broiler chickens access to trees before, no-one as far as we know, had combined a fully commercial venture designed to be profitable with a properly replicated experiment designed to be scientific. In fact, several people told us before we started that it was impossible to do both, so we found ourselves trying to prove them wrong as well as all the other things we were doing. In fact our experiment, which we nick-named PINE (Poultry In Natural Environment) took on a life of its own and provided a way of answering at least four different sorts of questions, some of them scientific and some of the commercial.

Our first question was the overall one about the system that any farmer thinking of starting up a chicken business would want an answer to: can you take an empty, tree-less field, plant young trees and profitably rear free-range chickens in small units? The system was run with the help of the Food Animal Initiative (FAI) at Oxford and the Northmoor Trust at Little Wittenham, both of whom needed to make a profit to cover their costs in the way that any other farmer would.

Our second question was the one that prompted our interest in the first place: is chicken welfare really improved by planting trees and encouraging them to range or is it just that we humans fondly imagine that it is? Given that we were starting from scratch with a completely tree-less field, a sub-question here was whether any benefits from trees would be apparent even with newly planted woodland rather than already mature trees that many farmers, like us, would not have available.

We also had a third question: might chickens also be good for trees? Would the young trees benefit from the natural fertilizer that the chickens were being encouraged to desposit under them and, more importantly, might the chickens eat or destroy competing vegetation and so reduce the need for spraying herbicide to keep down weeds?

Our final question was about the environmental impact since there would be no case for promoting the system unless we could show that the system itself would not cause problems with pollution or loss of biodiversity. Would there be nitrate-run off or damage done to the environment through the impact of the birds?

So we had four questions and four elements: farmers, chickens, trees and the environment. Could there be mutual benefit all round? Could everyone win?

We set up identical systems at two separate sites, one at Little Wittenham and the other at the University Farm near Oxford. This straight away gave us information about whether different sites gave different answers to our questions. Our chicken unit was a "plot" of 1627 m2, which had on it either one small chicken ark (52m2 floor area), with its own windmill and solar panel, or two. As each ark held 670 chickens, the one-ark plots gave the organic outside range space allowance of 2.5m2 and the two-ark plots gave the free-range outside space allowance of 1.2 m2. Altogether, across the two sites, we had 16 of these chicken plots, but we also had another 16 identically sized plots that were left free of chickens so that we could monitor the impact the chickens were having. Of the 16 chicken plots, 8 were planted with young trees (a mixture of conifers and broad-leaves) and 8 were left as pasture only, so that we could compare the behaviour, welfare and productivity of birds kept with trees and those kept without. A steady stream of 1300 birds a week was supplied to a major retailer and over the course of the first 18 months of the study, we studied a total of 112 flocks, of them with trees and 56 of them without, a degree of replication enough to satisfy even a demanding statistician.

For the first three weeks of life, all the chicks were reared in brooder houses to keep them warm. Then they were moved into the arks, but the doors were kept closed for a few days, partly to protect them from the weather and partly to get them used to their new home. By the time they were 25-27 days old, the doors were opened and they could move freely in and out of the arks.

The first birds went out into the arks in January 2003, in the middle of cold wet weather. From that time on, our team regularly descended on the plots and made a battery of measurements. Ruth Feber and Katy James took vegetation samples, Gabriel Hemery measured tree growth and kept a careful eye on their progress. Tracey Jones and Marian Dawkins made weekly measurements of behaviour, including ranging, walking ability, foot and leg health. Curt Lambeth sank lysimeters into the soil and then fascinated the rest of us with his accounts of how water in the soil below the chickens was moving sideways across the field. Paul Cook supervised the collection of production data. Undergraduates doing their research projects counted invertebrates, looked at the development of ranging in young birds and studied the drinking behaviour of the chickens (and their prediliction for puddles). As a complete bonus, since it was not part of the original proposal, Frances Colles and Martin Maiden took regular Campylobacter samples and genotyped them with a view to seeing if our chickens were picking up infections from wild birds.

Three years into the project, and with a change of breed behind us, we can answer at least some of our own questions as well as many others. First and foremost, the system was a success commercially. Right from the start, the birds were successfully marketed as a valuable supermarket commodity. The idea of keeping birds in relatively small colonies is attractive to consumers prepared to pay more for high welfare specifications. An electric fence kept all but the most enterprising foxes out but crow predation was a bit of problem. Nevertheless, total mortality on the field averaged 6% in year 1, 3.2% in year 2 and 3.6% in year 3. Encouragingly, all flocks were Salmonella free.

Our second question - about the welfare of the birds with trees was not clear initially since tree-growth in the first year was hampered by the hot dry summer of 2003. In the first year, the chickens 'with trees' had in fact little more than tree-guards with a few leaves sticking out of the top, so it is hardly surprising that we were unable to pick up any radical differences in behaviour from the truly no tree condition. However, by the summer of 2005, when the trees had grown considerably, the numbers of birds seen outside in the plots with trees was significantly higher than in the plots without trees, particularly on sunny summer days. The trees were now definitely having an effect! And in the 112 flocks studied intensively in our first two years, we were able to find some very interesting correlations between flock behaviour and various factors in the environment. For examples, birds ranged more at the Northmoor site than at the Wytham site, possibly because there are more hedges and shelter at Northmoor. Not surprisingly, more birds ranged outside in the summer and autumn than in the winter and spring, correlated with external temperature.

On our third question (were the chickens helping the trees?) produced a somewhat puzzling answer. Trees survived the 2003 drought less well at Northmoor than at Wytham but those that did survive grew taller at Northmoor. Trees in plots without chickens actually grew taller than those with chickens but this does not seem to be a direct effect of chickens but possibly an indirect effect of the way weeds were controlled. We hope to be able to find out what effect chickens were really having by continuing our measurements as the trees grow.

Results on environmental impact, too, will have to await our longer term measurements for a final answer, but at least the results so far are encouraging. Most nutrient levels in surface and groundwater were low before chickens were introduced to the sites and remained low afterwards. Unexpectedly, plots with high chicken density have a lower mean nitrate concentration than plots without chickens, but this may simply have been due to the fact that groundwater flowed across the site and confounded any real comparison. Similarly, studies of the numbers of plant species were difficult to interpret because of initial differences between sites and at different parts of the fields. At least the chickens had no obviously damaging effects on the environment.

While the idea of chickens milling about under trees is very attractive to consumers buying chicken meat, there is nothing, absolutely nothing, that substitutes for putting an idea into practice and seeing whether it actually works. That is where the combination of the Food Animal Initiative and Defra-funded research is so powerful. By running the enterprise on commercial lines and having themselves to make a profit, FAI and the Northmoor Trust reassure farmers that the system is feasible and economic. By using relatively small units (that have the excellent spin-off of giving the scientists plenty of replication for their research), they can appeal to the small farmer who may be unwilling to invest a great deal of money all at once and wants to try things out on a small scale first. And then, by involving research scientists, they generate answers to fundamental questions about the value of the system to the birds themselves, whether their welfare is really improved and what chickens do to the environment.

But there is a further and perhaps even more important contribution that this highly successful hybrid between a commercial enterprise and a research project is making. This is that it allows the development and progressive improvement of the system itself. No idea or concept is likely to be perfect the first time it is put into practice, certainly not in agriculture, and the PINE system is no exception. No farmer wants to be the one to make the mistakes but many of them have already been surmounted and dealt with by FAI. Problems such as cleaning the houses, for example, have been solved by developing an ingenious system of plastic sheeting inside each house that is then wound out of the house by a tractor winch to remove the manure. The breed of chicken used has been changed from one that grew to slaughter weight at 56 days to one that was slower growing and kept until 81 days. The result is that we have built up a case lore of best practice, of what works and what does not. The commercial/ research hybrid is also a demonstration tool that can benefit the entire farming community.

And if trees are good for chickens and if chickens are good for trees, there could be longer term implications for the countryside as a whole. Chickens may be a way of encouraging the planting of more trees, since on their own, trees are not a very attractive investment. They take too long to yield any income. But by having a short-term return on the chickens, the longer term return becomes more attractive. Agroforestry - chickens and trees - could give economic benefits long before any income would have been forthcoming from trees on their own. All that and animal welfare too!


Jones, T.A., Feber, R., Hemery, G., James, K., Cook, P., C. Lambeth, Dawkins, M.S. Welfare and environmental benefits of integrating commercially viable free-range broiler chickens into newly planted woodland: a UK case study. Submitted to Agricultural Systems.

ThePoultrySite - March 2006

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