Wintering Whooping Crane Update
Wade Harrell, U.S. Whooping Crane Recovery Coordinator
Fall migration will soon begin and whooping cranes will start moving south out of their breeding grounds in Wood Buffalo National Park (WBNP). It was a good breeding year in WBNP. Above average water conditions contributed to an estimated 45 fledged whooping cranes that will soon be headed to Texas on their first migration. We usually expect to see the first whooping cranes arrive at Aransas NWR in early October. The whooping crane migration from Wood Buffalo to Aransas is about 2,500 miles in length and can take up to 50 days to complete.
Last fall, I outlined some of the places that whooping cranes stop to rest in migration. This fall, let’s take some time to look at some of the preliminary results from the whooping crane tracking study in regards to when, where and how whooping cranes perish. For years, scientists have thought that migration was the most dangerous time for a whooping crane, and hence the time period in which they were most likely to die. Our recent telemetry study is providing new information in this vein and is again reminding us that there is still much to learn in regards to whooping crane biology. Most of us don’t like to talk about death, but for a wildlife biologist, understanding more about mortality can help us improve management for whooping cranes and ultimately recover the species.
Tracking study and mortality:
From 2009-2014, a study led by the U.S. Geological Survey’s Northern Prairie Wildlife Research Center marked 68 individual whooping cranes with GPS transmitting devices. This equates to about 20% of the Aransas-Wood Buffalo population being marked. About half of the marked birds were marked as 1st year fledglings at Wood Buffalo and the rest as adults here on the wintering grounds. The information collected from these marked birds, consisting of 3-5 locations a day, 365 days a year, provides us an enormous data set that we are now starting to sort through. Once signals from the GPS transmitters indicate that a bird has quit moving, it is often a sign that the bird has died. We try our best to collect every carcass as quickly as possible once we have reason to believe the bird has likely perished. This is not as easy as it sounds, however, since GPS tracking technology still has a few glitches and these birds are often using remote and inaccessible habitat. Additionally, carcasses tend to degrade very quickly in the natural environment. Regardless, all collected carcasses are sent to the National Wildlife Health Center (NWHC) for necropsy and disease testing. The lab then provides us a report indicating likely causes of the bird’s demise.
Of the 68 whooping cranes we marked in the tracking study, we recovered the remains of 17 birds over a 4 year period (June 2011-March 2015). Here is a summary of what we have found so far:
1) Whooping cranes are most susceptible to dying at a young age. Only 3 of the 17 birds we recovered were classified as adults (> 2 years old). Keep in mind that whooping cranes are long-lived birds (<30 yrs).
2) Mortalities occurred across all seasons and times of year. When we discuss whooping crane management, we often divide up a year into four distinct time periods (summering, fall migration, wintering and spring migration). Whooping cranes spend about 5 months of the year at summering locations (WBNP) and another 5 months at wintering locations (on and around Aransas NWR). The other 2 months of the year they are migrating between summering and wintering locations.
More than 85% of the marked crane deaths occurred in summering and wintering time periods, with mortalities roughly equal between each time period. Thus, less than 15% of marked crane deaths occurred during migration. So, cranes deaths are evenly distributed across the year. Previously we thought that migration was a particularly risky time for cranes, given the potential hazards they face in their long journey. But the tracking study doesn’t indicate that this is the case. Keep in mind that the tracking study was conducted during a drought period here on the wintering grounds, and we know from past research that winter mortality is higher during droughts. Past research likely underestimated mortalities that occur in summering areas due to the remoteness and inaccessibility of WBNP.
3) Mortalities occurred in places you would expect, with all of the summering mortalities occurring in Wood Buffalo National Park less than 20 miles from the primary nesting areas. Wintering mortalities occurred throughout our primary wintering range (5 on Aransas NWR and 2 on private lands). Birds died in South Dakota, Kansas and Nebraska (suspected, no carcass) during migration.
4) Of the 17 recovered carcasses, the NWHC reports could only determine cause of death for 4 birds because most of the carcasses were too decomposed and deteriorated. Of the 4 known causes of mortality, two were from predation, one from a bacterial infection and one from an injury. While past research has noted a number of mortalities from power line collisions, this was not a cause of death in any of the marked birds. Perhaps our work to decrease this impact over the years with partners such as the Avian Power Line Interaction Committee has made a difference!
I’ve kept this summary short and left out a number of details, but the information I have included here is from a book that will be coming out next year if you are interested in learning more. Here is the citation:
Pearse, A. T., D. A. Brandt, M. Bidwell, and B. Hartup. In Press. Mortality in Aransas-Wood Buffalo whooping cranes: timing, location, and causes. The Biology and Conservation of the Whooping Crane (Grus americana), French, Converse, and Austin, editors. Academic Press.
For those that have an interest in the science of whooping cranes, keep your eyes out for future publications from the U.S. Geological Survey and other partners involved with the whooping crane Tracking Partnership. Additionally, we still have the Texas Parks & Wildlife video on this study posted on our website here.
When the whooping crane population started to crash in the early 1900’s, many whooping cranes were being killed by humans throughout their range. The picture of whooping crane mortality was much bleaker then than it is now. This ultimately led to the species being listed as endangered and extensive conservation efforts began taking place. We’ve made significant strides in recovering the species over the last 100 years, but we have a long way to go. Many of you have heard about the continued whooping crane poaching issues, particularly in our reintroduced populations. A recent article in Texas Monthly discusses a poaching case in Southeast Texas and our efforts to reestablish whooping cranes in Louisiana.
Waterfowl Hunter Outreach Efforts:
Given ongoing poaching issues, we are working closely with many of our partners to increase education and outreach efforts within the waterfowl hunting community. Day in and day out, hunters are our eyes and ears on the ground during the wintering season and they can be a tremendous help to the overall whooping crane recovery effort. Waterfowl hunters have supported wildlife and wetland conservation for years through their purchase of the federal “duck stamp” and are often the first to report problems occurring in wildlife habitat. We will be out in the wintering grounds during the next several months providing information to hunters on whooping crane identification and conservation. Additionally, our Law Enforcement Special Agents will be working during waterfowl season around Aransas NWR to educate hunters about the importance of whooping cranes.
Texas Whooper Watch
Be sure to report any Texas migration sightings via email: firstname.lastname@example.org or phone: (512) 389-TXWWW (8999)
Current conditions at Aransas NWR:
As we previously reported and was noted in a recent Victoria Advocate article, we had a few (3-4) whooping cranes that decided to stick around for the summer rather than make the long migration back to WBNP. While we don’t know for sure why this happens, we do know that it has happened in the past and is likely to happen in the future. We suspect that the birds that stayed were non-breeders, thus their hormonal triggers to migrate back to breeding and nesting areas in the spring may have been lacking. When this has happened in the past, birds may have been recovering from some sort of injury or illness. But the whooping cranes that stayed this past summer appear to be in fine health.
Food & Water Abundance:
Once again, whooping cranes will be arriving to lush conditions here in Texas. It appears to be another banner fall here on the Texas coast, with abundant food resources and wetlands full of fresh water. Our fire management staff has been busy using prescribed fire this summer to improve habitat conditions for whooping cranes and other wildlife, with around 3,800 acres on the Refuge burned so far in August and September.
The Refuge has received 6.8” of rain from July-mid September 2016, and the current forecast predicts that we will see more rain the latter part of this month and next. Salinity levels in San Antonio Bay are currently <10 ppt. and have remained low throughout most of the summer.