Using maths to decide when to put dogs on leashes

Reducing the threat to our endangered migratory shorebirds


Key messages:
  • We sought the most cost-effective allocation of patrol effort among sites with a limited budget to help manage disturbances to migratory shorebirds
  • We demonstrate a straightforward objective method for allocating enforcement effort while accounting for diminishing returns on investment over multiple visits to the same sites.

One dog’s fun is another bird’s terror. Repeated disturbance by dogs can stress and even kill shorebirds. (Photo by Kiran Dhanjal-Adams)

One dog’s fun is another bird’s terror. Repeated disturbance by dogs can stress and even kill shorebirds. (Photo by Kiran Dhanjal-Adams)

Going for an evening stroll along the beach with the dogs is a great way to end a hot Australian summer’s day. But, unbeknown to many, little migratory shorebirds are also often soaking up the late afternoon sunshine. These little creatures have made it all the way from their breeding grounds in eastern Russia and Alaska, to spend the Australian summer feeding on the abundant sea life found in the intertidal zone. Like Zen masters, they patiently wait until the tide has gone down to gorge on worms, shells and crabs, before retreating as the tide comes back in. They must then wait until the tide withdraws to feed again.

This feeding period, during low tide, is critical to these birds. Many will have flown non-stop all the way from Alaska to Australia, some 11,700 km in 6 days! That’s like doing 293 marathons in one go. And like someone who has just run a marathon, migratory shorebirds are hungry. They will have lost between 50-80% of their body mass during this spectacular journey.

Migratory shore-birds (ruddy turnstones) are foraging for food at low tide. (Photo by Kiran Dhanjal-Adams)

Migratory shore-birds (ruddy turnstones) are foraging for food at low tide. (Photo by Kiran Dhanjal-Adams)

One dog can easily spook a flock of hundreds of birds. If this happens once, it is not so big a deal. But I have counted up to 1 dog per minute on some Australian beaches. That is 60 dogs in one hour and 120 in 2 hours – that’s a lot of disturbance! Repeated disturbance can be highly detrimental for the birds as it forces them to leave a good feeding area for not-so-good feeding areas. And even if they move, dogs are likely to be wherever they move to.

Anything preventing birds from gaining enough weight can mean they are unable to migrate. It might even kill them.

This is a big problem. Many species of migratory shorebird are in rapid decline across Australia. Several species have been recently listed as threatened under the Environmental Protection and Biodiversity Conservation Act. In Moreton Bay, for example, some species have declined by 50-80% between 1995 and 2009.

Moreton Bay near Brisbane is a popular place for shorebirds and people (and people’s dogs). Between 1995 and 2009 some species have migratory shorebird have declined around Moreton Bay by 50-80%. (Photo by Kiran Dhanjal-Adams)

Moreton Bay near Brisbane is a popular place for shorebirds and people (and people’s dogs). Between 1995 and 2009 some species have migratory shorebird have declined around Moreton Bay by 50-80%. (Photo by Kiran Dhanjal-Adams)

While this is all quite depressing, there are several simple steps we can all take to minimise impacts on shorebirds. First up, restrain your dog. I have had 6 dogs in my life, and all of them have been fond of chasing birds – pigeons in particular. I am always careful to keep my dog on a leash near wildlife. I also walk around flocks of birds, not through them. It’s easy, yet it makes a big difference.

But not everyone is aware of the plight shorebirds or the need to give them peace, and local shorebird managers are encouraged to carry out information campaigns. And this is where a little decision science can help. Given they must also manage commercial and recreational fisheries and tourism on top of shorebirds, there is a need to optimise where and when they carry out information campaigns to avoid wasting precious time and funds, while delivering the best possible outcomes for the birds.

Consider this, if you have 10 sites that you could visit between 0 and 5 times, there would be a total of 60,466,176 possible combinations of site visits. How would you figure out which of these possible combinations delivers the best outcome?

A few other numbers and a bit of maths will help here. How many birds are at a site? How many disturbances? How much will it cost to manage that site? With this information it is possible to do a cost-benefit analysis to determine which combination of site visits delivers the best outcome within the specified budget.

However, the more you visit a site, the more you will start talking to the same people over and over again about shorebirds. There is, therefore, a trade-off between visiting a site too much and wasting your time talking to the same people, or visiting a site too little and not talking to enough people.

How do you explore this trade-off? We attempted it by expressing the trade-off as a mathematical formulation (Dhanjal-Adams et al, 2016). We found that if management was effective (ie, that almost everyone started putting their dog on a leash after talking to marine park officials), then it was best to manage a lot of sites a few times. However, if management was not very effective (ie, that only a handful of people started putting their dog on a leash after talking to marine park officials), then it was best to find sites with lots of birds being disturbed, and repeatedly visiting them. This ensures as many people as possible are persuaded to keep their dogs on a leash near shorebirds.

Dogs and shorebirds don’t mix and many species of shorebird are in dire trouble. How much effort do you spend patrolling a range of shorebird sites to ensure people are doing the right thing? (Image by David Salt)

Dogs and shorebirds don’t mix and many species of shorebird are in dire trouble. How much effort do you spend patrolling a range of shorebird sites to ensure people are doing the right thing? (Image by David Salt)

These methods apply to a range of management scenarios extending well beyond shorebirds. Say for instance you are deciding which sites to visit to ensure as many rhinos as possible are protected from poaching, or where to patrol to ensure fish stocks are not depleted. All that is needed is information on target species (average number of rhino or fish), infractions (numbers of caught poachers or illegal fishers) and the cost of patrolling (how much petrol do you need to get to those sites).

It’s important to note that enforcement is not the only tool available in the manager’s toolbox. For shorebirds, for example, better dog walking facilities (where dog owners can go and let their dogs run off-leash) would reduce the number of people walking their dogs on the beach, and would in turn reduce the need to carry out information campaigns.

The underlying message is that everything is a balancing act, and successful conservation requires a mix of community involvement, government engagement and implementable management plans. Engaging communities and governments is a long and complex process, but devising cost-effective management plans need not be so with the right tools.


More info: kiran.dhanjal.adams@googlemail.com

Reference

Dhanjal-Adams KL, K Mustin, HP Possingham & RA Fuller (2016). Optimizing disturbance management for wildlife protection: the enforcement allocation problem. Journal of Applied Ecology 53: 1215–1224.

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