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Last summer I was going fishing as part of an inland fisheries class with North Carolina State University’s (NCSU) Wildlife Summer Camp. While I was walking around the pond to secure a section of the bank to fish, I stumbled upon a baby white-tailed deer, which was curled into a ball near the pond bank. It didn’t move or make a sound. In fact, I reached down and scooped it into my arms before my teacher, a deer researcher at NCSU, and classmates caught up to me. Because we were part of a class, we had appropriate permits to handle wildlife (don’t try this at home). We learned how to age the fawn based on size and behavior and determined it was only seven days old! The fawn was not stressed, so we took pictures, before releasing it back where it was hiding. We loved the experience of seeing a wild deer fawn up close, but why hadn’t the little guy run away as we approached?
Deer fawns are covered in hundreds of white spots (300 on average) that help to camouflage them. For the first one to two weeks of life, white-tailed deer rely on this camouflaging pattern to protect them from predators. Rather than fleeing at a sign of danger, fawns stay motionless to avoid detection. Mothers commonly leave their fawns for hours at a time, before returning to let the fawn nurse. The following photos show how well fawns are camouflaged (note that the young were radio-collared as part of a research project).
During the second week of life, young deer are steadier on their feet and will flee rather than sit still when threatened. By the fourth month of life, the protective white spots that once covered their fur start to disappear. Predators remain a threat to deer and after losing their camouflaging spots, these young deer must find new ways to avoid predation. Mainly, they adjust by being on the lookout for predators, and then running away as fast as they can if they sense danger. When deer are looking for predators, they are exhibiting what we call vigilance behavior: they hold their heads high, often with perked ears, looking and listening for potential threats. However, vigilance comes at a cost; there is a trade-off between having your head up to keep an eye out for predators and having it down near the ground to browse for food. Thus, vigilance behavior can directly influence the health of each individual deer because it takes away from the amount of time they can spend foraging. Of course, vigilance is worth it because it helps keep them alive if deer-eating predators are stalking nearby.
Scientists are increasingly interested in measures of deer vigilance because it provides a window into how deer see the world – a direct way to measure how nervous a deer is. With a metric like this, we can start to ask questions about what types of things make a deer more or less nervous, and therefore, more or less able to browse the local vegetation. Camera traps and direct observations are ways researchers can watch this behavior and several new studies report factors that influence deer vigilance.
In one study on deer vigilance in North Carolina, researchers baited 100 motion sensitive camera traps and used the pictures to determine how often the animals had their heads up looking for predators, or down munching the corn bait. After coding the behavior of 40,000 deer photos they discovered that deer increased their feeding time (i.e. were less nervous) as their social group size increased. Their results make sense; more eyes in the group allowed individuals more time for feeding, rather than looking for predators. They also determined that males were less vigilant than females, meaning they spent more time foraging. The researchers hypothesized this behavior was due to males’ larger body size, which might make them less likely to be attacked by a predator (primarily coyotes at this site).
Another project with elk in Montana found that all-male herds were less vigilant than herds with females, and that a higher calf-to-cow ratio resulted in a more vigilant herd. The North Carolina deer study also found this result: when fawns were present, females were more vigilant than when no fawns were present.
The North Carolina study also evaluated vigilance compared to time of day and moon phase. Deer were less vigilant in the afternoon and during brighter moon phases, likely because they were better able to see approaching predators.
Meanwhile, another group of researchers in Poland determined that olfactory cues, like fresh wolf scat, also affect vigilance in red deer. Red deer doubled their vigilance behavior when wolf scat was present, suggesting that predators’ scent alone can put deer on high alert. When deer smell that predators may be nearby, they are much less likely to forage, but rather spend their time looking for those predators.
Together, these studies show that camera traps can be great tools for studying the factors that affect deer predation risk. They have confirmed the importance of group size in protecting against predators, and suggest that prey also adjust their defenses daily based on light levels, and locally if they smell a predator. However, I think we are just starting to scratch the surface at what else we can learn about predator-prey systems with this new vigilance measure, and I’m happy to be helping with a new study that extends this past work by analyzing deer across 32 parks in the eastern United States.
eMammal is a citizen science research project that enlists local volunteers to run camera traps and then share the pictures with scientists. At the Biodiversity Lab of the North Carolina Museum of Natural Sciences, we are now going through these pictures and quantifying how nervous each deer is, how often they have their head down to feed, or up to look around. This data set is stratified across areas of different human use, so we will be able to evaluate the effect of people, as well as coyotes, on deer behavior. Some of our cameras are in hunted parks, while others are in unhunted lands. Some are on busy hiking trails, remote hiking trails, or off in the middle of the woods, allowing us to also check to see if human foot-traffic is important to deer. Finally, we also get counts of coyotes on these cameras, so we will factor them into the analysis as well.
I often come across fawns in the pictures we are using for this study and laugh as they play or chase insects in front of the cameras, always thinking back to the fawn I found last summer. Although we don’t have any conclusions yet from these images, we will soon be able to add up all of our data and plot results – I can’t wait for that eureka moment. Whatever we discover, I will present a poster on this research at The Wildlife Society meeting in October.
Follow me on Twitter @sumdawg to see the best pictures from the research!
It may be a mouthful to say, but Comet 67P/Churyumov-Gerasimenko — partly named after its co-discoverers — made history today as the first comet to encounter and undergo synchronous orbit with a human-made spacecraft, which will eventually land on its surface, and follow it over the next several years as it nears the Sun. Known as Rosetta, this international mission is a cornerstone of the European Space Agency’s Science Program. Today, it made its first rendezvous and orbit with its icy comet target.
Rosetta and comet “Chury” (for short) are locked in orbit at about 405 million km from Earth. When Rosetta lands on Chury, it will conduct scientific measurements of chemistry and physical properties on a comet nucleus, feats never before possible with the fly-by missions of the past. Solar system scientists hope that the information gained by Rosetta will unlock clues to the origin of the solar system, some of which lie hidden inside some of the most primitive, and hard to reach bodies of the solar system — the comets.
The comet will eventually pass far beyond the orbit of Jupiter, accompanied by Rosetta.
Today’s feat was accompanied by new images (“Postcards”) of the comet’s surface, such as the one below.
This is the last chapter of our story about a great egret that we gave a GPS tracking device on the Outer Banks of North Carolina in spring 2013 (see photo). We followed his movements for about 8 months and reconstructed his story with his GPS and ACC data (see parts I, II, III and IV).
This was the first time that an egret’s migration has been recorded in such detail and, as you could see through this blog, we learned some quite amazing things about this bird.
Mr. Bisbing had spent his summer within the Outer Banks, breeding and raising chicks with a mate, then taking it easy in the wetlands south of Roanoke Island. As the days became shorter toward the end of September, he started becoming unsettled, and on October 24th he took off, flying south over the open ocean. He migrated all the way down to Colombia, stopping for a few days in the Bahamas, Cuba, and Jamaica.
Finally, when Mr. Bisbing arrived in Cesar Province, Colombia, our data show that he started foraging in the same routine manner detected while he was in North Carolina (Fig. 1).
Suddenly, on Dec. 8th his movements stopped. His tag was still sending data, so it must have been in a sunny location to keep powering the solar panel of our tag. It took us a few days to realize that the tag had completely stopped moving, and that Mr. Bisbing had probably died, or possibly dropped the harness off his back.
Our next challenge was to go to the site to see if there was a dead bird, and recover the tag, so that we could download the detailed data (the daily text messages from the tag to us just sent us a subset of the data) and analyze the results. We started asking around among colleagues and birders to find someone locally in Colombia who would be able to search for the tag at this the GPS location.
On March 3rd, Mr. Curtis Smalling (Director of Land Bird Conservation, Audubon North Carolina) sent a note to the group, ProAves, a Colombian bird group, asking if anyone would search for the radio-tagged egret for us. On March 20th, Dr. Matthew Godfrey (sea turtle program leader, NCWRC) informed us that he gave all the information we had provided to him to his Colombian colleague, who in turn, posted the request on the Colombian Bird Network.
On March 19th, we received an email from Magaly, who told us that she would search for the tagged bird! We found a biologist, who was willing to help us, far away in Colombia!!! She asked a few questions about the frequency of the tag and the exact GPS location, then started her search.
She found the tag exactly where we thought it was, and also the feathery remains of Mr. Bisbing in Plot No. 16 of the San Miguel, Vereda, The Navajo town of El Copey Cesar, Colombia. We are very grateful that Magaly volunteered to take her time to recover and send the tag back to the Museum of Natural Sciences in Raleigh.
But what caused Mr. Bisbing’s death? The area that he chose to forage in had been affected by an unusual summer with no rain in five months and the vegetation was very dry as evident in pictures from the area (Fig. 2).
The only water sources were man made wells for cattle. One of the farm workers (Fig. 3) reported to Magaly that he had seen the dead heron and its transmitter about two months before she arrived looking for it. He did not handle the dead bird but observed, that he “did not see any wounds on the bird”.
We assume that Mr. Bisbing died of starvation and exhaustion after the long migration. He chose a foraging area that didn’t provide enough food to recover from his depletion of reserves. Was he inexperienced in this area, or was it the unusual summer that turned his trip into a disaster? We will never know about this individual bird, but if we keep observing more egrets and follow their way through life, we will hopefully understand more about how and why they choose locations to spend the summer or winter, and what their preferred migration pathways are.
We have tagged other great egrets and found that they each have an individual schedule and have quite different preferences regarding foraging areas or migration routes. You can see their movements on movebank.org and find out in which areas Ms. Palma, Mrs. Newbern, Mrs. Kelly, Mrs. Heller, Mr. Norvell, and Mr. Meadows preferred to live and migrate.
With the detailed observation of Mr. Bisbing, for example, we found that at least this bird preferred migrating during the night. There are only a few observations of migrating great egrets reported prior to our study, and they stated that great egrets migrate during the night. We were pleased to find that these older reports were confirmed by our study.
This new, detailed knowledge about breeding behavior, foraging preferences, migration pathways and timing, etc. will help us protect great egrets and increase their survival in our more and more urbanized environment.
You can participate and help us in these efforts, too, by using a new application called Movebank. With this app you can follow birds live in real-time, and go out in the field to find the tagged birds, take pictures and send them back via the application. So give it a try, check out the location of the closest bird, get into your car and enjoy the search.
This is the fourth chapter in the story about a great egret that we gave a GPS tracking device on the Outer Banks of North Carolina in spring 2013 (see photo). We followed his movements for about 8 months and reconstructed his story with his GPS and ACC data (see parts I, II and III).
On October 24th at 9 p.m., Mr. Bisbing took off for his last long trip. Up to that point he had spent his summer within the Outer Banks, breeding and raising chicks with a mate, then taking it easy in the wetlands south of Roanoke Island. Everything seemed to be orderly and his daily routine was relaxed and regular. As temperatures got colder toward the end of September, he started becoming a bit unsettled. He checked out new foraging areas, drifted farther and farther south, but still returned to his roost every night. Eventually, he overcame his inhibitions and took off flying south away from the Outer Banks, over the open ocean.
During his migration, Mr. Bisbing covered a total of about 3200 km (2000 miles) (Fig. 1). He started with an impressive 22.5-hour nonstop flight (from Oct. 24th, 9 p.m. until Oct. 25th, 7:30 p.m.) from his roost south of Roanoke Island straight across the ocean to the Bahamas, where he took his first break. During this first nonstop stage he covered more that 1200 km (about 755 miles)!
But why do egrets migrate at all? Bird migration is the regular seasonal movement, often like in our case, north and south along a flyway between breeding and wintering grounds. Migration carries high costs in predation and mortality but many species of birds have to risk it because of the availability of food. Great egrets like Mr. Bisbing feed on fish and other small vertebrates such as amphibians, reptiles and mice. During winter all these vertebrates appear less abundant, because many of them hibernate. So egrets need to find foraging areas with higher abundances of their preferred food.
Timing of migration is controlled primarily by changes in day length. For navigation birds often use celestial cues from the sun and stars, the earth’s magnetic field, and probably also mental maps. Mr. Bisbing flew across the ocean, during the night, so we can assume, that he had no visual orientation to navigate. Nevertheless he found his way back to a shore and foraging grounds to regain some strength. We were quite surprised to observe that when migrating, Mr. Bisbing was flying actively, flapping his wings nonstop, without soaring as birds of similar size and body shape like storks or cranes do (Fig 2).
After his first landing in the Bahamas, he rested for only 80 min before he flew farther south for another 35 min. Here, in the south of Greencastle, he found a wetland and rested for the rest of the night. He slept-in the next morning and took off at 9:40 a.m. to forage in the surroundings. But he took only one day to recover from the long and exhausting flight, spending his time resting and foraging (Fig. 3).
Why Mr. Bisbing didn’t stay in Bahamas longer we will never know, but in the evening of October 26th at 8:00 p.m., he flew another 435 km (270 miles) south over the Caribbean. It took him 6 hours, and by 2 a.m. he reached the northeast coast of Cuba. He rested there for a few days in a quite regular daily pattern, as he used to do before the migration: waking up at 7 a.m. and spending the day foraging until 8 p.m., when he went to bed at his roost (Figs. 4 and 5).
Our ACC data record ends on Nov. 2nd at 1 a.m.. We were not able to download any data from the memory card during Mr. Bisbing’s migration, so the ACC memory card filled up and stopped recording. From now on, we don’t have any more details about his body movements, but we could still follow his regional movements, because the GPS was still working. The resolution was lower, due to the memory limitation, but we received a few points every day to follow his large scale movements.
After 20 days in Cuba, Mr. Bisbing was on the move again, migrating 400 km (about 250 miles) farther south to Jamaica on November 15th. He found a roost south of Pamphret (Fig. 6) and stayed in this area for almost two weeks, until November 27th.
The next data we received are from November 29th, and at this time, Mr. Bisbing is already in 960 km (about 600 miles) farther south in Colombia, south of Momil in Cordoba Province, where he stayed for another day. From there he flew another 212 km (133 miles) farther northeast, to Cesar Province. The GPS tells us that he arrived here on December 2nd and he stayed and foraged in this area for another couple of days – until his movements stopped on December 8th. This was the last step of his migration, indeed, the last flight of Mr. Bisbing. What happened next to our tragic hero, and how we got the tracking tag back from South America to North Carolina will be the subject of our final blog post about Mr. Bisbing the great egret.
This is the third chapter in the story about a great egret that we gave a GPS tracking device on the Outer Banks of North Carolina in spring 2013 (see photo). We followed his movements for about 8 months and reconstructed his story with his GPS and ACC data (see parts I and II).
On July 17th Mr. Bisbing got up before dawn (5:05 am to be precise) and took off for a major change in his life. Breeding season was over, his offspring were on their own by now, so he could have some fun in a maybe more diverse environment.
So he took off, flying south, along the coastline (Fig. 1). After 45 min he took his first break right behind the city of Duck at the beautiful sound. During this first stage of his trip south he covered about 32 km (20 miles). But the new area seemed not to be very interesting, at least we couldn’t observe any foraging behavior in the Accelerometer (ACC) data (Fig. 2), so he took off again at 6 am and flew for another 12 min, 9 km (5.6 miles) further south. He rested again, maybe checking for some food, and as nothing interesting showed up, he kept going south. On the whole Mr. Bisbing took 6 stages to cover a distance of about 71 km (44 miles) which took him about 70 min flight time and a little over 4 hours all together.
Eventually he arrived at 9:20 am at his new home for the rest of the summer: a small island between Hog and Cedar Island in the south of Roanoke Sound.
After this long and strenuous flight Mr. Bisbing was certainly hungry and needed a meal, so he started foraging and spent the rest of the day island hopping around his new roost site, searching for food (Fig. 2). The first night was a little rough, and it took him until midnight to finally settle down and sleep calmly (Fig. 3), but from the next day on, he fell into a regular and relaxed routine.
Mr. Bisbing usually woke up around 5:40 a.m. and left his roost around 5:50 a.m., quite punctually every day. From the roost, he first flew south to the wetlands of an island west of the Oregon inlet (Island C). He spent most of the day there, but sometimes checked the wetlands east of the Bodie Island Lighthouse or east of Tommy Hammock, before he went back to his roost for the night between 5:30 and 8:30 p.m. (Fig. 4).
He stayed in the area south of Roanoke Island until October 24th, but decided that another change was necessary on Sept. 27th. From that day on, he roosted 5 km (3.1 miles) farther south on Island C, west of Oregon Inlet. This was the island where he used to go foraging every day. He also changed his foraging preferences. From now on, he chose more and more often to forage south of the Inlet, an area, that he didn’t use before at all (Fig. 5).
As autumn wore on and temperatures got chilly, his daily schedule became more and more irregular, and his foraging trips took him farther and farther south. He flew up to 19 km (12 miles) south from his roost to forage – a long distance for a daily routine. Perhaps this was training to get prepared for his next big adventure – a huge migration south of the Outer Banks, heading out over open ocean. Read more about it in our next post in a couple of days!
This is part two out of five of our story about a great egret that we tagged at the Outer Banks in Spring 2013. We followed his movements for about 8 months and reconstructed his story with his GPS and ACC data (see part I).
The exact position of the lines in the ACC graph are the result of totally different behaviors, giving us clues about important events in Mr. Bisbing’s life. While the motion of the bird is recorded by changes in lines on an ACC graph, the relative position of the lines to each other show the position of the bird relative to gravity. Leading up to May 19th, Mr. Bisbing would occasionally rest at night in a horizontal position, motionless, with the blue line above the green line, different from his roosting position, which was green line over blue, over red (Fig. 1).
So we concluded that this horizontal posture was actually Mr. Bisbing incubating eggs, sitting all the way down on his nest to keep them warm. This was exciting news! Our tagged bird was going to have babies!
We observed this incubation position only until May 19th, presumably the hatching date. Prior to this date, he incubated every other day or so, sometimes up to 52 hours in a row (May 13th)! Egrets take turns incubating eggs, and we could observe that Mr. Bisbing took turns with his partner because he roosted at places other than the nest.
During these first 3 weeks, from April 21st until May 19th, Mr. Bisbing foraged in two different areas. After waking up and doing his morning grooming, he flew either north, towards Swan and Johnson Islands and spent the day there foraging in the surrounding wetlands, or he flew south to forage in the wetlands west of Corolla. Once in a while he made his way along the coastline, probably searching for new foraging grounds, but always returning to his two favorite wetlands where he spent most of the daytime (see Fig.2).
Then, during the night of May 17th, something exciting seemed to happen. The GPS data show that Mr. Bisbing stayed on the nest for almost 60 hours in a row, until 6:20a.m. on May 19th. The ACC lines tell us little more details about what happened during this time (Fig. 1).
On May 17th Mr. Bisbing flew back to his nest in the evening and settled down in the incubating position. He stood up once in the middle of the night (the switch from blue over green to green over blue), probably to stretch his legs and neck. During the next day he stayed in the incubating position, but moved around quite a bit, more than during other incubating periods– was he nervous? Something seemed to bother him – was there something going on with his eggs?
But he calmed down again in the late afternoon, the lines are flat again. During the following night he switches into the roosting position, still at the nest site. Maybe he took a turn in incubating with his partner. The next morning, he incubated for another 3 hours – the last time that we observed this behavior. When he stood up again he started moving around but stayed close to his nest as the GPS data tell us. Great Egret young usually hatch one at a time, so we assume that those days were probably the time when Mr. Bisbing’s chicks were hatching.
After May 19th, Mr. Bisbing changed his daily schedule. Before that day his routine was rather irregular, including long periods of rest in different places, long periods of incubating and foraging in many different areas. After May 19th, Mr. Bisbing chose the wetlands west of Corolla as his absolutely favorite foraging site. He went there in more than 90 % of the time during the next two months and he flew north only twice, towards Johnson and Swan Islands (see fig. 3).
We assume that the wetlands west of Corolla became the new preferred foraging area, because it’s only half the distance compared to Swan and Johnson Islands. By choosing the closer food source, Mr. Bisbing could save time and energy, which he urgently needed to feed his offspring.
Surprisingly he left the nest all day and came back only in the evenings to help feed the chicks. Typically he took off early in the mornings, around 5:30 a.m. and came back before dusk, between 6 and 8 p.m.. This behavior is likely caused by the remote location of Monkey Island and long commuting time to get there. Long flights cost time and energy, and as Mr. Bisbing was raising his chicks he needed to budget these factors.
Another interesting fact was that he slept on Monkey Island, but at a roost away from the nest, for 12 nights in a row. Furthermore, on three occasions he didn’t come back to Monkey Island for 48 hours. For a new dad, he certainly was avoiding the nursery. However, after these initial days of fatherhood, he slept at the nest in his roosting posture except for three nights. It’s not quite clear to us, why he behaved this way. Maybe his wife took good care of the chicks during the night, so that he could rest and get ready for the next day’s foraging trip.
Other studies have found that great egrets feed their offspring at the nest for 20-30 days, depending on the local food supply. Egret chicks start clambering from the nest after about three weeks and fly away from the colony after 1-2 months. We cannot tell from our data, when Mr. Bisbing’s chicks left the nest. But we do know, exactly when he left the colony – [July 17th, 5:05am] – never to return. Find out where he went in our next blog in a few days.
How often do you see a bird flying high in the sky and wonder where it’s going? Some birds make amazing migrations of many 1000s of miles – how long has that bird already been flying? How much farther does it have to go? Migratory birds must have amazing stories to tell, but we are left to imagine the details as we watch them fly overhead.
Modern technology is now revealing these stories in amazing detail – new tracking tags use GPS to record location and a 3-axis accelerometer (ACC) to record their behavior. These solar powered units work 24/7, anywhere on the globe, for the entire lifetime of an animal. Here I want to show you one example through the life and death of Mr. Bisbing.
“Mr. Bisbing” was a male Great Egret. He was a slender, good-looking guy of average size and, as we found out later, he was in a productive relationship. We met our protagonist at the Whalehead Club in Corolla, North Carolina, where we lured him into our traps with bird decoys and a bucket of fish (more in this Untamed Science video).
Once we had him in our hands we gave him a high-tech backpack a GPS and ACC tag (Figure 2). We released him on April 21st , 2013 at 11:40am, in front of the Outer Banks Center for Wildlife Education, and followed his every movement for the next seven and a half months, until his untimely death.
We immediately learned an important part of Mr. Bisbing’s story: he had a nest on Monkey Island. The GPS data showed us that he went there every night. There’s a known egret colony there, and our tagged bird was obviously a member of this group. Looking very carefully at the GPS data we realized that he used two different parts of this small island: one spot on the south that was his nest and another spot to the north where he must have gone when he needed to get out of the house (Figure 4).
The ACC sensor records 3 dimensional movement of the bird that we can use to learn about the behavior of the bird. The graph below (figure 5) shows three lines describing the bird’s movements in three dimensions: up and down (blue), forward and backward (green) and right-left sway (red). Different behaviors of the bird create patterns that we can identify. In the resting position, all lines are flat. When an animal is walking, each foot-step creates a similar, but slightly delayed pattern in the blue and green. The wing-beats of a flying bird show the strongest peaks in blue. The ACC data are recorded in high resolution every 4 minutes, for 4 seconds at a time.
The following graph shows you what Mr. Bisbing’s typical day looked like (Figure 6). Early in the morning, before dawn, he freshens up and goes for breakfast. In this example (May 24th) the GPS shows that he flies from his nest on Monkey Island 3.7 km (2.3 miles) to the wetlands west of Corolla. In the ACC data you can see from the width of the blue high amplitude peaks that the early morning flight away from Monkey Island and the evening flight back to Monkey Island take longer than the short flights around the wetlands during his foraging behavior. The sleeping position during the night is also easy to recognize because the bird is motionless.
Now you have met our main character and know the cool things this technology can tell us about his life. In my next post I’ll dive into the details of family life on the Outer Banks.