Archive for the ‘Census Flights’ Category
Whooping Crane Census Flight April 7, 2009
April 8, 2009The tenth aerial census of the 2008-09 crane season at Aransas was conducted April 7, 2009 with USFWS observer Tom Stehn in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions of Castroville, Texas. Viewing conditions were ideal with clear skies and light winds, although turbulence made the ride uncomfortable most of the time. Nearly all parts of the crane range were flown.
Migraton
Today’s flight tallied 103 adults + 6 juveniles = 109 total. Thus, 56% of the flock has started the migration. Whooping cranes have been confirmed on April 2nd as far north as Nebraska. I expect a considerable number of cranes will start the migration in the next week. Conditions should be ideal for departure with very strong southeast winds forecast for Aransas April 8-9.
Whooping Crane Numbers
With estimated losses that have occurred at Aransas this winter, the current flock size is estimated at 225 adults + 22 juveniles = 247. The estimated peak winter flock size was 232 adults + 38 juveniles = 270 total.
Mortality
Today’s flight provided evidence of 2 additional mortalities, with total winter mortality now estimated for the winter at 7 adults and 16 chicks totaling 23 whooping cranes, a loss of 8.5% of the flock that was a record 270 in the fall. In the last 20 years, the current winter ranks as the worst in terms of mortality, ahead of 1990 when 7.5% of the whooping cranes (11 out of 146) died at Aransas. The 3rd worst winter in 1993 showed a 4.9% loss at Aransas (7 out of 143). Mortality in the 2008-09 winter (23 birds) can be added to the 34 whooping cranes that left Aransas in the spring of 2008 and failed to return in the fall. Thus, 57 whooping cranes have died in the last 12 months, or 21.4% of the flock of 266 present at Aransas in the spring, 2008.
The 2 additional mortalities confirmed on today’s flight that had been reported earlier by volunteers and staff are as follows:
Tour Boat Naturalist Ray Kirkwood had seen March 19-29 the Rattlesnake Island juvenile with a very bad limp, using its wings when it moved to try to reduce the weight put on its injured leg. The bird retained flight ability but was lethargic and may have stopped eating. The chick was not observed on April 1st when I looked for it from a boat and had presumably died. The pair believed to be its parents was observed on their territory on today’s flight with no sign of the juvenile.
The second mortality involved a grouping of 1 adult with 1 chick observed twice about 4 hours apart on April 1st in the marsh west of the airstrip on the south end of Matagorda Island. This same grouping of 1+1 was observed on their East Bray territory on today’s flight, providing confirmation that one adult has died.
Sightings near Aransas
Three whooping crane subadults that used the farm fields south of Austwell for much of the winter were last reported present on March 14th. They have either returned to the salt marsh or have started the migration.
Habitat use
For the first time all winter, nearly all the whooping cranes were found in the salt marsh on today’s flight. The cranes are believed to be feeding on fiddler crabs since blue crabs in the marsh ponds are still scarce due to the continuing drought. A blue crab count done on April 1st found zero crabs in the marsh.
Whooping crane locations on the flight included 2 observed at man-made fresh water sources, 2 at a game feeder, and 9 in open bay habitat. No cranes were on burned or unburned uplands. Tides were low caused by a very strong “norther” that had brought northwest winds on April 6th. Salinities remain high, measured recently at 29 ppt in the refuge boat canal and 39 in the adjacent marsh. One monitoring station in San Antonio Bay has a salinity of 25 ppt. The drought rated as “exceptional” shows no sign of ending in central and south Texas. Many counties have imposed prescribed burn bans due to the fire danger. Corpus Christi, Texas is 4.5 inches below normal rainfall starting January 1st.
Overall, these continue to be some of the worst conditions I have ever observed for the cranes at Aransas, with some birds looking thin and with disheveled plumage. The refuge is continuing its program of supplemental feeding with corn. A moderate response by the whooping cranes has continued. The cranes are getting somewhat of an energy boost by catching fiddler crabs just prior to migration.
– By Tom Stehn – Aransas National Wildlife Refuge
Whooping Crane Census Flight March 15, 2009
March 18, 2009The ninth aerial census of the 2008-09 crane season at Aransas was conducted March 15, 2009 with USFWS observer Tom Stehn in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions of Castroville, Texas. Viewing conditions were less than ideal with overcast skies and occasional light rain. Parts of the crane range were not flown as rain and lightning ended the flight after 3.7 hours.
Whooping Crane Numbers
With estimated losses that has occurred at Aransas this winter, the current flock size is estimated at 226 adults + 23 juveniles = 249. The estimated peak winter flock size was 232 adults + 38 juveniles = 270 total.
Mortality
Today’s flight provided evidence of 3 additional mortalities, with total winter mortality now estimated for the winter at 6 adults and 15 chicks totaling 21 whooping cranes, a loss of 7.8% of the flock that was a record 270 in the fall. In the last 20 years, the current winter ranks as the worst in terms of mortality, ahead of 1990 when 7.5% of the whooping cranes (11 out of 146) died at Aransas. The 3rd worst winter in 1993 showed a 4.9% loss at Aransas (7 out of 143). Mortality in the 2008-09 winter (21 birds) can be added to the 34 whooping cranes that left Aransas in the spring of 2008 and failed to return in the fall. Thus, 55 whooping cranes have died in the last 12 months, or 20.7% of the flock of 266 present at Aransas in the spring, 2008.
Four dead whooping cranes have been picked up this winter; at least two were emaciated, and the virus IBD (infectious bursal disease) has been isolated from one of the juveniles by Dr. Hon Ip at the National Wildlife Health Center in Madison, Wisconsin. It is not yet known if this strain of IBD is pathogenic to whooping cranes, but it seems probable. The 4th carcass discovered this winter was an old pile of white-plumaged feathers discovered March 2nd during a blue crab count conducted by volunteer Katherine Cullen and two Chinese biologists. The two Chinese that have cranes on their refuges in China expertly identified the feathers. On today’s flight, observations confirmed that one additional adult is missing leaving a one-adult family just south of Panther Point on Matagorda. Also, the refuge’s Pipeline and Matagorda’s Airport juveniles are missing and listed as dead. These last 3 mortalities had presumably all occurred prior to the February 25th flight, with observations on today’s flight confirming the losses.
Migration
One juvenile whooping crane was confirmed on the Platte River in Nebraska on February 20th. This is presumably the juvenile that had over-wintered in Oklahoma and probably moved north with sandhill cranes. It was still present on the Platte through March 9 and presumably is still there.
I have been asked how the current poor conditions of the cranes may affect the migration. I have no idea how that may affect the timing of the migration which seems to vary by only about one week from year to year. Low numbers of whooping cranes start leaving Aransas the last week in March, with the majority of the cranes departing the first 2 weeks in April. The last of the breeding pairs have all gone by April 21st; a few subadults occasionally stay into May. I expect the migration to proceed normally, with birds making it all the way to Wood Buffalo National Park in Canada. However, mortality in the migration could increase. My next census flight is scheduled for the week of April 6th to see how the migration is progressing.
Sightings near Aransas
Three whooping crane subadults continue to use farm fields south of Austwell. They were seen in a pond next to an agricultural field on March 12th, but were not searched for on today’s flight due to lack of time.
Habitat use
Management practices are aiding the cranes this winter. Crane locations on the flight included 7 observed at man-made fresh water sources, 17 on burned uplands, 33 on unburned uplands mostly foraging for tubers where feral hogs have rooted up the earth, 4 at game feeders, 1 on a well pad, and 23 in open bay habitat. Two cranes were on a recent burn on Matagorda Island conducted March 10th. Tides have risen somewhat since the previous flight on February 25th. Salinities remain high, measured recently at 30 ppt in the refuge boat canal. The drought rated as “exceptional” shows no sign of ending in central and south Texas. Many counties have imposed prescribed burn bans due to the fire danger. However, rain received in south Texas on March 14-15 has helped a little.
Blue crabs are still scarce due to the drought. These are the worst conditions I have ever observed for the cranes at Aransas, with some birds looking thin and with disheveled plumage. I wish I had better news to report. The refuge is continuing its program of supplemental feeding with corn. A moderate response by the whooping cranes has been observed with 76 photographs taken by remote motion-activated cameras in the past week of whooping cranes at refuge feeders. Other animals eating the corn include feral hogs, deer, raccoons, grackles and just a few remaining wintering sandhill cranes.
The USFWS used 2 airboats the week of February 23rd to pick up 411 abandoned crab traps in the crane area. This was done in conjunction with a program organized by Texas Parks and Wildlife Department to pick up abandoned traps all along the Texas coast. Waters within the boundary of Matagorda Island National Wildlife Refuge have recently been closed permanently to commercial crabbing with signs posted at most entrances into the marsh.
– By Tom Stehn – Aransas National Wildlife Refuge
Last year the decision was made by the Florida Fish and Wildlife Conservation Commission (FWC) to discontinue the release of whooping cranes into Florida's non-migratory flock. The FWC accepted the recommendation from the multi-agency International Whooping Crane Recovery Team. The team created the release program 15 years ago in an effort to establish a self-sustaining, non-migratory whooping crane population in Florida. Naturally occurring whooping crane populations in the southeastern United States disappeared by the 1930s. Scientists decided to stop releasing cranes into the non-migratory flock for a variety of reasons, including problems with survival and reproduction, both of which have been complicated by drought. Additional considerations included shorter-than-expected life spans, scarcity of birds for release, project costs and the loss of habitat from development. The team felt that project resources and birds produced in captivity could be better used for other whooping crane releases as well as to maintain the captive flock. Marty Folk, whooping crane project leader with the Florida Fish and Wildlife Conservation Commission continues to monitor the population and has provided an update report concerning the 2009 Breeding Season. Marty reports that, "Conditions have been very dry in Florida for several years. Attached is an image we recently took of a small lake in Lake County. The area outlined in green is the normal shoreline. All marshes in this area are completely dry. The drought continues but despite that, we now have an active nest. This pair's marsh holds water only because of a hydrological connection to a large lake. As you know, the goal of this project now has shifted to an emphasis on increasing our knowledge of the problems, especially regarding reproduction and survival. Toward that end, we are monitoring the nest intensively by employing video surveillance. There's a chance we might see several other nest attempts this year, but we don't expect more than 3 nests from the population's 11 pairs. The current population consists of 11 males and 18 females." Marty continues, "Drought is an obvious problem for breeding, but even in wet years some pairs failed to hatch eggs, so we are looking at incubation behavior to see if some pairs don't incubate 'properly'. We are computerizing a back-log of surveillance video that will allow us to look for problems with behavior by comparing successful vs. unsuccessful pairs. Thus far we have computerized >800 hours (that's not a typo-800 hours) of incubation behavior and still have a lot to go." Marty advises that in addition to long-term drought, other major problems include survival of individual whoopers. Marty explains that, "Male Florida whooping cranes are not living as long as they should; the general rule is that they die by age 10. Females are doing better and 9 birds are >9 years of age (the 2 oldest are turning 16 this spring).However, for both males and females, we don't have good data on what happens to them when they "disappear". Some birds, at time of disappearance, did not have functioning transmitters and so could not be tracked. Even for birds with functioning transmitters, if a carcass is not retrieved within 24 hours of death, scavenging and decomposition make it very difficult to determine cause of death. Others likely dispersed beyond a reasonable tracking distance and were never seen again." Florida wildlife officials are attempting to get a better understanding of the problems by intensive monitoring. Marty describes, "When we plot dates of mortality/disappearance by age, we see that most older cranes die/go missing from March-June. With that knowledge, we've begun an intensive monitoring schedule that involves checking high-priority (older) birds on a daily basis. We've not monitored this intensively since the early days of the project; our normal schedule has been 2-3 checks/week. Our hope is to recover downed birds asap so that necropsies can provide the best possible data." Marty concludes that, "We do know that perhaps one reason males don't survive as well as females is that they are more prone to power line collisions, and may be more prone in general to other traumatic events and also predation. We speculate that it is associated with the males' role in defending a territory, and also the males' general tendency to lead the group. So now we are collecting behavioral data on who leads flocks of whooping cranes, both in flight and on the ground, to look for trends." The Florida whooping crane team has been flying roughly one day/week to track migratory whooping cranes this winter. From the ground they have also been able to monitor 4 migratory birds in Polk County (the ultra-light led whoopers).
March 3, 2009Tom Stehn, USFWS biologist, Aransas National Wildlife Refuge and assocates recently completed another census of whooping cranes at Aransas. Stehn reports that, “The eighth aerial census of the 2008-09 crane season at Aransas was conducted February 24-25, 2009 with USFWS observer Tom Stehn in a Cessna 210 piloted by Gary Ritchey of Air Transit Solutions of Castroville, Texas. Viewing conditions were very good for the survey, although strong winds made for a very choppy ride.”
Stehn advised that, “We found 238 whooping cranes, but time limitations required us to fly at
greater speeds making it likely a few whooping cranes were overlooked. Strong tail winds and full power gave us at one point a maximum recorded speed of 198 mph on our GPS.”
Whooping Crane Numbers
The estimated peak winter flock size remains at 232 adults + 38 juveniles = 270 total. However, the last two census flights have documented additional mortality that has occurred at Aransas. I estimate the current flock size to be 228 adults + 25 juveniles = 253, but this figure may change depending on future observations.
Mortality
Mortality this winter is currently estimated at 4 adults/subadults and 13 juveniles totaling 17 whooping cranes. This is a loss so far of 6.3% of the wintering population (17 out of 270). The all-time worst winter on record was 1990 when 11 out of 146 (7.5%) whooping cranes died at Aransas. In the last 20 years, the current winter ranks as the second worst in terms of mortality, but we still have one month to go. The 3rd worst winter in 1993 showed a 4.9% loss at Aransas (7 out of 143). Mortality in the 2008-09 winter (17 birds) must be added to the 34 whooping cranes that left Aransas in the spring of 2008 and failed to return in the fall. Thus, 51 whooping cranes have died in the last 12 months, or 19.2% of the flock of 266 present at Aransas in the spring, 2008.
Three dead whooping cranes have been picked up this winter; two were emaciated. The wing from a juvenile whooping crane was picked up by refuge staff in the North Pt. Pasture on February 13th. The remainder of the carcass was in the mouth of an alligator at a freshwater dugout. This chick from the North Dunham Point family had separated from its parents as observed by staff on January 29th and February 11th. It presumably was sick and/or emaciated, a factor that contributed to its separation and made the juvenile vulnerable to predation.
Migration
One juvenile whooping crane was confirmed on the Platte River in Nebraska on February 20th. This is presumably the juvenile that had over-wintered in Oklahoma and probably moved north with sandhill cranes.
Sightings near Aransas
Three whooping crane subadults continue to use farm fields south of Austwell. They were seen in a pond next to an agricultural field.
Habitat use
Management practices are aiding the cranes this winter. Cranes on the flight included 28 observed at man-made fresh water sources, 9 on burned uplands, 13 on unburned uplands mostly foraging for tubers where feral hogs have rooted up the earth, 18 at game feeders, 1 on a shell road, and 20 in open bay habitat. Some water is starting to move back into the coastal salt marshes, although much of San Jose Island remained as dry tidal flats. Salinities remain high, measured at 30 ppt in the refuge boat canal. The drought rated as “exceptional” shows no sign of ending in central and south Texas. Many counties have imposed prescribed burn bans due to the fire danger.
Blue crabs are still scarce due to the drought. The refuge is continuing its program of supplemental feeding using corn. A moderate response by the whooping cranes has been observed with 100 photographs taken by remote motion-activated cameras in the past week of whooping cranes at refuge feeders. Other animals eating the corn include feral hogs, deer, raccoons, grackles and sandhill cranes.
The USFWS used up to 2 airboats the week of February 23rd to pick up abandoned crab traps in the crane area. This was done in conjunction with a program organized by Texas Parks and Wildlife Department to pick up traps all along the Texas coast. Volunteers running private boats picked up many traps on February 21st.
