Earth & Sky

The following individual was interviewed for today’s show. Our thanks to:

David Carter
Environmental Program Manager
Delaware Department of Natural Resources Environmental Control
Delaware Coastal Programs

Interview:

ES: Please tell me something about yourself:

DC: My name is David Carter, I’m Environmental Program Manager with the Delaware Department of Natural Resources Environmental Control, Delaware Coastal Programs.

ES: Thanks for talking with me today. Will you please tell me about the work you’ve done monitoring the suite of Delaware shorebirds, and in particular the Red knot?

DC: We’ve focused most of our attention on the birds up here on Delaware Bay. They typically arrive on May 10-12, and then leave by the end of the month. Best we can tell is that a large concentration of birds concentrate here in Delaware Bay. We don’t know exactly what the population size is, hemispherically, so we’re doing some work every year catching, color marking, by putting little plastic bands around their legs that we can scan and get population estimates for. We also do what are called biometrics, where we take a lot of measurements like the bird weight, wing size, bill size, that enables us to look at the health of the birds that are stopping by, and also let us know how much weight they’re putting on here. They feed on horseshoe crab eggs, and typically a little more than double their weight while they’re here.

ES: Wow, how long does it take them to double their weight?

DC: Well, they tend to double their weight in about 10-14 days. And typically they’ll come in anywhere from 90-110 gm and leave somewhere at 200 gm. And we’ve actually captured birds ? we caught one last year ? that put on about 45-50 gm a day for two days. They can move pretty quickly.

ES: Why are these birds so hungry?

DC: A lot of them appear to be flying from South America; in large part it looks like a lot of them come from Brazil and Argentine areas in a straight flight. So when they actually arrive in Delaware Bay they’re in what we call a fat-free condition, where they’ve actually burnt so much energy in the migration that they’ve actually burnt some of their muscle tissue as energy for their flight. Then they have a very short time window where they have to fatten up and have enough energy to fly up to the Arctic and also have enough to sustain them under cold conditions and things like that when they arrive in the Arctic to reproduce. And the total (distance) is about 10,000 km or so.

ES: Could you tell me a little bit about what makes the Delaware Bay area an Important Bird Area, what are some of the characteristics of the Bay that are important to birds?

DC: Well, the main thing that occurs with these shore birds is that they come in for Horseshoe crab egg. Horseshoe crab eggs spawn in incredible densities in Delaware Bay. And in recent years that’s been concentrated on the Delaware side of the bay. There has been some overharvesting of the eggs, but the data is still not clear whether there is a problem. And we actually went through a peer review to sort that out. So we need a lot more scientific data. But we get millions of Horseshoe crab coming through, spawning on the beaches, and under a good spawn they leave sometimes _ inch to an inch of solid green eggs, that are tiny eggs, 3-4 mm in diameter, which is a giant, smorgasbord supermarket for these guys to pig out on!

ES: I understand that the crabs don’t make it easy for the birds to get to their eggs, in that they typically bury them out of reach. How do the birds get to them then?

DC: Well, it depends. We do have some bird species, like Ruddy Turnstones that actually go into the beach and are very adept at digging in, getting down to the eggs, and tossing them up. What we’re also taken a really hard look at over the last five years are what ? both natural and nonnatural factors ? in terms of the habitat conditions, sand grain size, allow those eggs to come up to the surface. So in some cases, when the Horseshoe crabs spawn very densely will come in and burrow and dig up previously laid eggs and get them to the surface, making them available. The other thing that happens is that when we get on-shore winds with some good wave energy, those waves work that sand down to the depth of the eggs and bring a lot of them up, making them available to the birds.

ES: Now this 10,000 km trip that some of these shorebirds take, is that typical for migrating birds?

DC: Well, Red Knots right now, and in particular this hemisphere’s Red Knots that are actually a separate race that occurs in the Eurasian flyway that goes on through Africa, best we can tell, is the longest migration known on an annual basis for a species. It’s pretty much phenomenal. On some of the others, like Sanderlings, they don’t go quite as far south. And the only other bird that we knew went a little further than this was the Eskimo curlew, which for all practical purposes, is believed to be extinct. So they are a very unique long distance flyer and migrator.

ES: Could you talk a little more about the relationship that shorebirds have with this unique habitat?

DC: Well, it’s the only place where we get this really heavy concentration of Horseshoe crab eggs, and I think that over the years they have just evolved with them. And the other hypothesis that’s been out is that in recent centuries that they’ve concentrated the Horseshoe crabs into this area and that led to the concentration of the birds. It’s difficult to tell because market hunting at the turn of the century had just about decimated these bird populations that are very low so there aren’t a lot of good records historically of of what populations were and where they were seen. For the most part these birds feed on bi-valves, small muscles, clams, and those type of things everywhere else in their flyway. So it’s a unique thing for them to feed on the eggs here in Delaware Bay, and maybe it’s a very energy rich source. It may be that it’s so abundant that there’s an ecological pay-off for them, an evolutionary pay-off for them. But they tend, throughout their flight, to go from one flight to the next where they have this incredible, super-abundance of food that allows them to really put on this incredible weight gain so that they can make it all the way up for the rest of their migration and be able to be successful at breeding.

ES: What are some of the factors that affect the availability of Horseshoe crab eggs?

DC: Well I’m sure there are several. We see annual weather making an impact. The amount of harvesting, and if there are harvesting and overharvesting issues, that’s something to consider. The quality of the habitats and the beaches that are there are one that we’re looking very seriously at. And, quite frankly, we don’t know what the impacts of sea level rise are. We’re seeing increased sea level rise, and that’s changing our coastal shorelines, the birds might not be adapting as well as we’d like them to, as quickly as we’d like them to.

ES: Is there particular time when the egg availability is most vulnerable?

DC: Yes, these birds time so that they come right at the very early stage when the eggs become available. And that starts in early May and then peaks in late May when they’re really putting on their weight. And we have seen, in 1998 for instance, we had several north eastern storms come up on the Delaware Shoreline where water didn’t drop, didn’t make the beaches available for spawning or for the birds to use them, and that was a very difficult year, there just wasn’t much around for them. And I think they’re a long-lived species, maybe 10-15, some a little bit longer, is how many years they’re going to have to breed, so they’re going to have good years and bad years. And that’s just the gamble you take in the wild, it’s a tough world out there!

ES: Is it possible that they might all get wiped out by a bad event?

DC: I think that’s an overstatement. We can say that if that happened over a long period, I think it would have population problems. And there’s a debate over whether that’s happening. The fact that they come in one year and have a tough time means that probably they won’t have a good breeding year. And the only time I can really see where that might occur is where if they all came in and we had an oil spill, and it oiled a huge part of this population. I can see a problem if they came in and didn’t have eggs available and/or not enough eggs to make weight gains to make it up to the Arctic and had a very cold, cold spring where the snow wasn’t melting. In the Eurasian flyway that they’ve been studying for forty years, when they’ve seen large drops in the population, it’s usually been correlated very closely with very harsh, cold winters in the Arctic breeding grounds where you just have something happen, they get up there, they have some bare ground, they start to set up nest, and then they get a cold blast that really takes them out. That’s when you see them. But anytime you have a species that concentrates such a large, large percentage of the entire hemispheric population in an area that could be 2-3 km of beach in Delaware Bay in any given year, they are susceptible. You know, you truly have put all of your eggs in one basket. And there’s always a risk for a species that does that. But there must be some evolutionary pay-off as to why they do it.

ES: What do you mean by “evolutionary pay-off?”

DC: Essentially, over time they adapt, they change biologically and behaviorally to environmental conditions that lead to successful reproduction and sustaining the population. So the things that benefit them the most are the things that they evolve to be able to do. And that appears to be having them all converging into these super abundant areas. As a large population, there may be advantages. For instance, if there’s a large flock of peregrine falcons coming down to eat you, well if you’re in a big flock, perhaps you have bigger protections or a better chance of seeing them and being able to take evasive action. So these are the things that over time, increase your chances of survival and reproduction and keeps your species going, it’s straight out of Darwin.

ES: What kind of bird traffic come through this area, like for instances the Red knot?

DC: We’re not sure, but it’s common to have a half million, a million shorebirds of 10-15 species. For Red knot the population might be 75-150 thousand birds in the entire hemisphere, and I personally have been with a team where we have counted about 50 thousand of them all on on beach that was about a kilometer in length. So that’s probably in one tiny, tiny place along the flyway is comparable to the size of a needlepoint, and we have half of the entire hemisphere’s population there.

ES: What are some of the other things you’d like the public to know about the work you’re doing?

DC: Well the big thing is that it wouldn’t be possible to in our case without the enormous amount of assistance that we’re getting from the British “” Ornithology and the “” “” Group. These are groups out of the United Kingdom and they have about 40 years of experience doing this kind of long-term research studies and banding and cannon netting with shorebirds. They’ve come over annually and provided training and assistance to us and have really helped us to develop this program we hope will be able to do the longer term and help to answer these difficult questions with a lot of public policy ramifications, and one of the real goals that we have is that we have been, the environmentalists and the fisherman have been in a combative state and we believe that really, the only way that we’re going to get common ground and these people to be able to work together and quit disputing these things is to get really good science , and based on that science make good management decisions based on fact. And people will be willing to accept that scientific information and let us act accordingly rather than just pointing the finger and yelling “The sky is falling.” It may or may not be, but we really need to understand a very complex ecological question here, and I think science and good research , good monitoring, is the only way that we’re going to do that.

ES: How important do you think these shorebirds are in the ecological “big picture?”

DC: There are several ways you can look at it. Just from an evolutionary perspective I think that it’s just an incredible natural phenomenon that you don’t see at this magnitude anywhere else in the world. When you talk about internationally, as shorebirds go, Delaware Bay is largely recognized as the “Mecca,” and I think that’s a world-wide recognition. And then there’s the “” Wadden thing in Europe and others have some really wonderful things. Of course the copper delta in Alaska is another one. It is a truly unique natural phenomenon that are just breathtaking to see. This is stuff that’s just amazing. When we set up national park systems, John Muir years ago saw things that were in the natural environment that were worth saving for future generations and we’re managing and keeping, and I think there’s some intrinsic value to that. From an economic perspective I think that the Horseshoe crab I think is a renewable resource. We have a long-standing culture of fisherman that use Horseshoe crabs for healing and things that are traditional cultural values that we need to maintain. We have huge biotechnical and medicinal values that come from the “” of the Horseshoe crab eggs that really has huge public health benefits. So there are a lot of benefits that we need to balance and work on, and it’s just a tremendous resource that gets people very emotional, and as a manager you have to balance all of those needs , all the societal needs and do the best that you can based on good information to do the right thing for the public.