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For the Birds: The Science Behind Recent Bird Die-Offs

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With the New Year came a number of mass animal deaths across the country, including the 3-5,000 red-winged blackbirds that fell near Beebe, AR, beginning on New Year’s Eve. The U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis. is investigating the cause of the AR bird deaths, as well as the smaller die-off of about 500 birds that occurred in Louisiana on January 3rd. The preliminary findings suggest that these birds died from impact trauma, and further tests are pending. USGS scientists Paul Slota and Scott Wright discuss the NWHC response.




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Marisa Lubeck: Welcome and thanks for listening to this episode of CoreCast. I'm Marisa Lubeck.

With the New Year came a number of mass animal deaths across the country, including the 3-5,000 red-winged blackbirds that fell near Beebe, Arkansas, beginning on New Year’s Eve. The U.S. Geological Survey’s National Wildlife Health Center in Madison, Wisconsin is investigating the cause of the Arkansas bird deaths, as well as the smaller die-off of about 500 birds that occurred in Louisiana on January 3rd. The preliminary findings suggest that these birds died from impact trauma, and further tests are pending.

I'm here with USGS scientists Paul Slota and Scott Wright who have been studying the birds at the Center.  Thanks for speaking with me, Paul and Scott.

What does impact trauma exactly mean, Scott, and what caused the trauma in the Arkansas birds?

Scott Wright: Impact trauma is a term that we use to differentiate different things that might have caused the birds to appear the way they do when we conduct the necropsy, which is an autopsy of animals. And what we look for are specific appearance of organs and blood and so forth that might be where it's not supposed to be and that sort of thing, as a result of the birds striking either a flat or blunt surface as opposed to a sharp surface. So impact trauma in this case means that the birds struck something that was blunt or flat.

What we looked for are tears in the organs, some broken bones, and hemorrhage, which means there's free blood in places where we wouldn't normally find it like within the body cavity. All of these are indications of type of trauma, in this case, from blunt surface.

Marisa Lubeck: Is there any link between the Arkansas event and the bird deaths in Louisiana?

Scott Wright: Well, the only links that we are aware of based on the evidence we have is that one, similar species were involved in both events, that is red-winged black birds. Two, based on the appearance of carcasses we received from Louisiana, they also struck objects, but in this case it was power lines.

Marisa Lubeck: Paul, the National Wildlife Health Center has been stressing that while bird die-offs are concerning, they're actually somewhat common. How often do events like this occur and why don't we hear more about them?



Paul Slota:  That's a really good question. The National Wildlife Health Center investigates almost to 150 to 200 wildlife mortality events every year. These are just the epizootics or epidemics that we investigate and it include birds, frogs, salamanders, bats--a number of species. Now, that averages out to close to a report every other day and some years, more than that. If we just look at the bird events for 2010, we've recorded eight events involving more than 1,000 birds. For the past 10 years, there had been 188 events involving more than a 1,000 birds. So relatively speaking, 2010 was a fairly quiet year.

Now, most of these reports come to us from refuge biologists and wildlife biologists that manage really quite large tracks of land and along with that are large wildlife populations. So most of these events don’t occur in urban areas and residential areas and I think that’s why this event is creating so much notoriety: Because it occurred in a relatively, heavily populated residential area and that is very unusual. But I think it’s not quite as unusual as what people might think.

Marisa Lubeck: What other noteworthy animal die-off events has the center worked on in the past?

Paul Slota: Well, the most interesting one to me was an investigation that I was involved with in the 90s that involved the emergence of the West Nile virus. Beautiful Fall day, we began receiving unexplained reports of dead crows, and this often did involve residential areas. Now crows are really tough birds, so this was something of an anomaly. At about the same time, in the New York area, zoo birds were dying and in some of the hospitals, people were being admitted with some kind of strange symptoms. The National Wildlife Health Center worked with the Centers for Disease Control, as well as the veterinary community, to figure out that in this case all of these events were related. We ended up documenting the emergence of this new disease into North America. So this was the first time that scientists were able to document a new event occurring.



Marisa Lubeck: Why is the National Wildlife Health Center particularly involved in this investigation and what unique resources does it have to offer that make it useful in such cases?

Paul Slota: The USGS National Wildlife Health Center is basically the only federal laboratory that’s dedicated to the study of wildlife health from a national perspective. So we work with federal, state, and other natural resource agencies throughout the entire United States to investigate wildlife health and disease issues.

In this case, we’ve been using our facility and our staff to support state investigations. So it’s important to distinguish that these two events in Louisiana and Arkansas are actually being investigated and managed at the state level and that we’re just providing the scientific support on the diagnosis. And we’ve been doing this for well over 35 years with a very specialized facility in which we’re able to safely work with disease agents, as well as a very specialized staff consisting of wildlife biologists, pathologists, microbiologists, chemists, veterinarians. We even have a dedicated facility engineer to ensure that our facility is under very tight containment so that anything we’re working on doesn’t get into our local community.

Marisa Lubeck: Can you walk us through the testing process once you receive the birds from the states? Scott, what sorts of tests, for example, are performed and when will the lab results be available?

Scott Wright: The most important thing that we do is get as much information as we can, as soon as we can, from the local investigation – the folks that are at the area where an event occurs--whether it’s this one in Arkansas or any other one--to help us think about the circumstances that might have been involved in these animals' deaths. Once we receive the carcasses, we do very careful external examination and very comprehensive internal examinations looking for evidence that might suggest the cause of death, collect appropriate samples for testing based upon what we observed and what we have learned from the local investigation.



In this case, we’ve done testing for potential pesticide poisoning or other types of poisonings and some of those results are still outstanding but we’ll receive them soon. These are what we called rule-outs. The idea behind this is to make sure we have covered different bases to consider all the different types of things that might have occurred. Once this information is put together, we then have a story that’s composed of the laboratory analyses and pathology--what we see in the carcasses--combined with the information received at the local investigation. These two major pieces put together a story of what this event was all about.

Marisa Lubeck: Paul, if mass die-offs happen relatively frequently, why is it important to study these individual events so thoroughly?

Paul Slota: We're always concerned about these events and we think it’s very important to investigate and understand them so that we can learn how we might control them in the future. And if we can’t control them, at least reduce their frequency or magnitude. A few years back, there were mallard ducks that were dying on the reflecting pond in front of our US capital. This also triggered reports of people getting sick. And some of those birds were put in a FBI jet and flown to Madison and within a fairly short period of time, we were able to show that the birds died of avian botulism, which is a really common disease in birds. And now the National Park Service routinely cleans the reflecting pond and we have not had any reports of birds dying again.

It demonstrates the need to carefully investigate these events so that we can tell what events are fairly common versus events like West Nile which were very uncommon.

Marisa Lubeck: The media have been reporting on this die-offs consistently since New Year's. Scott, have you ever worked on an animal mortality event of this magnitude before and what have things been like for you and your colleagues at the National Wildlife Health Center this past week?



Scott Wright: I’ve worked on multiple events like this throughout my career. I think the major difference between some of these other events and this one is these two unrelated but simultaneous events received an enormous amount of media attention. But putting this in perspective with some other events that are more current, certainly the emergence of White Nose Syndrome in wild bats over these last several years has drawn a great deal of attention on the part of the scientific community, but not as much on the part of the public--or at least a much slower progression of interest on the part of the public. But from a biological perspective the overall effect of White Nose Syndrome far surpasses anything we’ve seen in these recent events involving red-wings in Louisiana and Arkansas.

In terms of our staff, many of them worked very hard to provide as much information as quickly as we could to the investigators that are responsible for wildlife management in the states of Louisiana and Arkansas. They asked for our assistance and really, I think this is a tremendous example showing how well we were able to interact with state agencies and other agencies in order to receive carcasses, conduct necessary scientific tests and then put together answers as quickly as we could. These all does a service to the public because, understandably, they were quite concerned. So it was important that we work together, hectic to be sure, but important that we work as hard as we could to get information out in a timely way, and that’s what a lot of folks did.

Marisa Lubeck: Have you learned anything new about the science you do from these bird mortality events and has anything interesting or noteworthy struck you during the study process?

Scott Wright: I think the circumstances surrounding the event at Beebe, Arkansas, was unusual in the sense that I’m not aware of our databases supporting an event like this that was a result of loud noise forcing birds off their roosts. However, it’s important that we document all of these events as much as we can. This gives us the opportunity to discover emerging diseases. For example, White Nose Syndrome was essentially started because of a phone call, because someone had some bats with white stuff on their muzzles.

So we learn something from just about everything we touch, and it goes into the overall mass of knowledge we have about wildlife and wildlife health across the nation.

Marisa Lubeck: Thanks for taking the time to speak with me today, Scott and Paul.  

This podcast is a product of the US Geological Survey, Department of the Interior. I’m Marisa Lubeck. Thanks for listening.


Show Transcript