There are many proposed solutions to solving the common resources problem (see some of my previous posts on common resources for some examples). However, the most sustainable solution is likely to be making the species excludable, rather than non-excludable. If you can prevent the hunters from hunting, then sustainability of animal populations will be much easier to attain. But how do you achieve excludability?
One option is farming. Have you ever considered why many bird species are threatened or endangered, but chickens are not? It's because most bird species are non-excludable (it's difficult to stop someone shooting or trapping a bird in the forest), but chickens are excludable because people own them (and presumably, chicken farmers watch their chickens at least closely enough that hunters wouldn't try to hunt them). Farmers also have large incentives to ensure that they keep their flocks sustainable (by taking out only the number of chickens that leaves a reasonably stable, or even growing, population).
However, for most birds farming is not an option. Some don't do well in captivity, and most of us would probably prefer that wild populations are kept sustainable, rather than developing increasingly in-bred farmed populations. So, we need an alternative option.
Fisheries in many countries are managed through transferable quota systems. Quotas regulate the number of fish that are allowed to be removed from the sea in a given period of time. The total quota is set by determining a total allowable catch for a year (in theory at least this is roughly equal to the growth in the fishery stock), with some allowance made for recreational fishing. Quotas work well because they make fish excludable (no quota means no fishing) and are backed up by monitoring and enforcement.
So I found this article from last week by Len Gillman (head of science at AUT) interesting. Gillman notes:
The kereru is a native New Zealand species protected under legislation, but despite this protection it has continued to decline in abundance since European colonisation. As an iconic native species, it is treasured by many Maori and Pakeha as something that must be preserved at all costs...
The main cause of kereru decline is predation and competition from mammalian pests, not hunting, and controlling these pests with natural poisons such as 1080 has been shown to promote their recovery. With ongoing predator control, populations increase until they reach a point where, limited by resources, surviving fledglings entering the local population roughly equal those leaving the population due to emigration and mortality.
When a population reaches stability, small harvests can be made without affecting the total number of birds, because those removed by harvest allow more fledglings to survive. This concept is known as a sustainable harvest - it allows a small ongoing harvest without affecting the size of the population. Harvesting quotas would need to be based on kereru numbers and age distributions, considering young birds learn survival skills from older birds, but sustainable harvesting holds great promise.
There are a couple of points to add to this. First, once the sustainable harvest number of kereru have been determined, how would the harvest be allocated? In other words, who would determine who has the rights to harvest kereru, and for how many birds? This sort of allocation problem is key (see here for a similar example relating to water).
Second, to ensure efficiency the rights should be transferable between parties in a voluntary exchange. Assuming that the rights to harvest kereru are only provided to iwi, and can only be transferred between iwi, this would still ensure that iwi who have the most to gain from harvesting kereru would be those that did the harvesting (since they would be willing to buy the rights off other iwi who valued the harvest less). This would ensure the maximum net gain for society (as a whole) from the limited (and sustainable) kereru harvest.