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Harrow Nature Conservation Forum
Requiring dogs to be on lead in Bentley Priory Nature Reserve - detailed arguments

There are a number of reasons, some obvious and some less so, why allowing dogs to run free over Bentley Priory damages the site as a nature reserve. We discuss the most important below.

A minority of poorly controlled dogs will attack cattle and wildlife. There have been a number of recorded instances of dogs chasing the cattle at Bentley Priory; in one instance a bullock was so scared that it jumped over a barrier fence. The cattle are important to the management of the grassland at Bentley Priory; if the grazier decided that the site was too dangerous for livestock and removed them (as he has talked of doing) then we would have to control the grass by mowing, which is not nearly as good at maintaining a complex mix of small scale habitats. We have witnessed dogs mauling wild deer; one instance was on Wood Farm in 2019 where the deer was so badly injured that we had to kill it. A recent report of dogs mauling a deer in Watford shows that this was not an isolated instance.

Even the best behaved dog, that would not hurt a fly, is percieved as a threat by wildlife. Ground feeding birds will fly up and wait in trees until long after the dog has passed; for hungry birds in winter, this can mean the difference between life and death. Birds nesting in bramble thickets will abandon the nest until they are sure that the danger has passed; while they are away the eggs may get cold or may be eaten by squirrels, magpies, grass snakes or even toads.

Peter Peretti, who was chief warden of Bentley Priory from 1989 to his death in 2022, was convinced that the increasing number of dogs on Bentley Priory was the main reason why the number and variety of birds on the site has declined drastically. His records show that in the years from 2012 to 2021, Willow Warbler and Yellowhammer were lost completely as breeding birds while breeding pairs of Garden Warbler and Lesser Whitethroat dropped by 30% and 75% respectively. Scientific research backs up Peter's view: a study in Australia found that dog walking in woodland leads to a 35% reduction in bird diversity and 41% reduction in abundance - and this was dogs on a lead, not free running dogs (Banks and Bryant (2007), Biology Letters, https://doi.org/10.1098/rsbl.2007.0374).

Clearly if the only objective was to maximize wildlife value, dogs would be banned completely from Bentley Priory. However requiring dogs to be on a lead will concentrate the impact on the strips of land adjoining the paths, allowing wildlife to live undistubed in the majority of the site (the Australian study looked at the number of birds within fifty metres of the path where leashed dogs were walked).

A less obvious problem caused by dogs is the fertilizing effect of their urine. On Bentley Priory, Spring Meadow and The Greedsward are beautiful in early summer when agrimony, knapweed, scabious, pignut and many other wildflowers bloom profusely. These lovely wildflower-rich meadows exist because the soil is low in nutrients. Where an area receives fertilizer, wildflowers are crowded out by ranker vegetation, especially grasses and bramble. To see the effect of this one only has to compare Spring Meadow and The Greensward, which have never recieved fertilizer, with Old Lodge Meadow which was treated with fertilizer in the past. Dog urine contains high concentrations of nitrogen and phosphorous, and dog urine has been shown to be a significant source of these nutrients in wild areas close to towns, significantly impacting the ecology (De Frenne, Cougnon, Janssens and Vangansbeke (2022), Ecological Solutions and Evidence, https://doi.org/10.1002/2688-8319.12128). Thus even well meaning dog walkers who collect and remove their dog's faeces are contributing to damage of the plant community of the site. Once again, if the only objective was to maximize wildlife value, dogs would be banned completely from Bentley Priory. However requiring dogs to be on a lead will concentrate the effect of the urine on the strips of land adjoining the paths, keping the majority of the grasslands in good condition and preserving the lovely wildflower swards.

The consultation also asks about dogs entering or remaining in ponds. Dogs love to jump into ponds, and denying them this pleasure seems cruel. No doubt an individual dog would not be much of a problem, but cumulatively, in the numbers visiting open spaces in Harrow, the effect are seriously damaging. The most obvious effect is on the waterfowl. Adults have to swim away or take flight; flightless babies are often caught and killed. But an even more serious effect is on plants and freshwater invertebrates. In a small pond, the clay stirred up by the dogs feet takes days to settle, so that no light can penetrate the pond water and no pond plants can grow. Much of the animal life in a pond or lake depends on the marginal vegetation: the reeds and other waterplants that are rooted in shallow water around the edge. Small fish hide among these plants to escape being eaten by larger fish and by cormorants; invertebrates such as damselflies and water scorpions cling to the stems. The cumulative effect of dogs scrabbling up the banks out of the water, dislodging plants that are trying to grow, is devastating. The two ponds at Roxbourne Rough in south Pinner, shown below, are a great example of this: one is fenced to exclude dogs, the other is not (the photos were taken on the same day in 2022).


Another, hidden problem is the flea treatment in dog's fur, which leaches into the water and harms freshwater invertebrates. A recent study of English rivers found that all those tested contained toxic levels of vetinary insecticide (Perkins, Whitehead, Civil and Goulson, Science of The Total Environment Volume 755, Part 1, https://doi.org/10.1016/j.scitotenv.2020.143560). In 2022 the charity Froglife launched the campaign 'pawsagainstponds' to alert dog owners to the damage dogs do to ponds and rivers. While streams in Harrow are heavily polluted from many sources - so polluted that most dog owners would not let their dogs jump in anyway! - rain fed lakes and ponds can be biodiversity hot spots. For example, the Dragonfly Ponds in Bentley Priory, close to the pill box at the top of Spring Meadow, is home to sixteen different species of dragonflies and damselflies, one of the loveliest group of insects. Making sure that dogs do not enter the water will help keep these ponds as havens for these and other aquatic life.

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