I’ve been slowly explaining the three axes that I’m using to look at habitat quality and conditions on the nonbreeding grounds: prey availability, predator risk, and human disturbances. I’ve alluded a bit to this third component - the disturbances - but I haven’t fully explained it yet.
I mentioned in the last post about this that an overwintering individual has two main ‘goals’ to survive and eat. But an individual’s ability to forage is linked to all three of these axes: it’s based on the prey availability (how likely a foraging attempt is to be successful), how often they have to look for predators which is time that they can’t eat, and similarly how often they are interrupted by people.
The beaches and bays in Chile are all public access - which is a nice thing compared to some of our private property beaches in the States, but it also means that there can be a lot of people utilizing these areas. We often see families swimming and picnicking, or sightseers taking photos of the swans or going on a walk. But there are also people using these areas for income.
There are fishermen in big boats, individuals collecting shellfish (mostly mussels), and individuals harvesting kelp. People drive up and down the beaches. Stray dogs (or owned dogs walking with a family) run around and chase birds. Barnyard animals roam freely through the mudflats. Boats and barges motor up to the tide line. Tractors drive back and forth between trucks and businesses and boats. There can be hundreds of people trying to utilize the same space that the godwits and other species are trying to forage in.
There are a few 'main’ concerns. Those individuals that are collecting shellfish and kelp are often following the tide line. There’s been reports of hundreds (literally hundreds) of people spread out along the tide line collecting kelp in some bays. Often they have boats or big carts pulled by oxen or horses to carry the kelp from the tide line to shore.
Godwits tend to forage right along the tide line where the mud is wet or in the water up to their bellies. They want to forage right where the people are. At Caulín, there are published reports of almost three hundred people and no godwits - there was no space left for them. The kelp is sold to the Japanese cosmetics industry, and it’s most likely harvested at rate that is un-replaceable. Little invertebrates utilize the kelp habitats and it appears to be a preferred foraging substrate for godwits. How does the harvest influence prey availability? And how is it affecting the invertebrate community long-term? How does the presence of people affect godwit foraging efficiency and decisions?
Then the actual person is also a threat and usually perceived by godwits as a predator. It can influence how much time they forage versus are vigilant. There’s a 'buffer’ around a person where godwits don’t seem to forage - a minimum distance to person, so if the people spread out enough then there may be more area disturbed than not.
There are a lot of questions and what ifs on the biological side, and it’s an interesting problem. The people harvesting kelp and shellfish on the flats aren’t the big bad corporations - they’re subsistence harvesters. Picking up some mussels and clams to make a traditional Chiloé dish - curanto - for dinner. Or collecting kelp to buy groceries. The human aspect is the flip side to this coin. How could we tell them that their livelihood is hurting the birds? Now that is a question I’m not ready to try to answer.
I’m interested in using some information we collect to look at the human disturbances on the flats in conjunction with the information on prey availability and predator risk to look at an individual’s decision to forage at that site. If a site has low predators, high food, but often has a lot of people collecting shellfish, would you decide to forage there?
We surveyed Caulín today and saw lots of kelp drying on the beaches from the morning tide. Not too many people out and about and we had what is now considered a big flock for this site about 2,500 godwits (numbers a decade ago were twice that before those published reports of 300 people). Within the flock we saw three FEGs that we’ve seen at Caulín before - including a male we hadn’t seen in a month! It was a really good scan!
Update: 29 individuals… Still