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Osprey Platform: 8 January 2021
Happy New Year! 2021 promises to be a good one. Great Horned Owls in our neighborhood are certainly making the best of it. In the last two weeks, we have documented a short, quiet and contemplative visit on December 22, followed by a whole lot of excitement on the 30th and Jan 2. This pair sealed the deal on their relationship by copulating followed by gifts. Did you know that female Great Horned Owls are quite impressed with offerings of fresh rabbit head?
Although this pair is visiting our platform and copulating for the camera, it still isn’t clear if they will stay. The last visits totaled a scant 4 minutes of hooting as the sun was began to rise on 3 Jan and a grunt on Jan 5, and some more hooting on Jan 7. Great Horned Owls are known to frequent several potential nest locations before definitively choosing their nursery. You may think that copulation means that egg laying is sure to follow. However, many birds have sperm storage, specialized structures that keep a male’s sperm healthy until the time is right for laying. Rest assured, in the next few weeks our camera will let us know if the platform was voted off the island, or is still in the running.
This week, a single and quiet Great Horned Owl visited the platform. In those few moments, one phenomenon jumps out at me, begging for an explanation. Why did the owl defecate moments before taking flight?
Most birds, like the owl, relieve their bowels prior to flight. Maybe you have experienced a poop-blizzard yourself, like this video of a snow goose tsunami (toward the end of the video look for the woman checking her hair for poo!). Expelling excrement before flight is fairly common among birds and is widely cited as a weight-reducing tactic to improve flight efficiency. A scatological study of Common Eiders found that the gut contents of birds in flight was 2 to 5 percentage points less than birds harvested when foraging in flocks. The birds were less likely to take flight when their guts were chock full of blue mussels, presumably because they were so heavy. We can imagine that our owl was a more nimble and effective hunter after lightening its load.
Boo hoo, it has been over a month since Great Horned Owls have visited the platform Do good things happen if you wait long enough? On Monday,a pair briefly visited the platform and sang a duet. Bird vocalizations are classified as songs or calls. Songs are usually loud, complex and function to advertise territory ownership. A Great Horned Owl song is the typical hoo-hoo, sung either by the male or as a duet with his mate. You can distinguish the sexes by the pitch of their hoots. Males are lower pitched than females.
Tuesday night, the female landed on the platform and called. Calls are usually shorter and more simple. In the video you hear a double squawk, or “wac-wac” call. “Wac-wac” calls are typically produced by females during nest defense and may function to summon her mate (Kinstler 2009).
This time of year (Oct-Jan) juvenile owls are dispersing and establishing new territories. This pair’s hooting and hollering is clearly communicating that this platform is part of their territory. Stay tuned and we will find out if they decide to use the platform for nesting in late January.
October 22, 2020
We never expected that this nest platform would become a perch for so many species of birds. This week the platform hosted a male Red-winged Blackbird singing, boat loads of Eastern Bluebirds, a Red-bellied Woodpecker, and an American Crow.
Notice that the crow picks up an owl pellet (there are two pellets on the platform, can you find them?). Crows are known to be curious and regularly manipulate new objects, often finding new sources of food in the process. Clearly the owl pellet is not appetizing once this crow got a closer look and taste!
October 12, 2020
After three weeks of little action, our Great Horned Owl returned, and was quite vocal. Owls hoot to maintain territorial boundaries. Hooting in the fall communicates to dispersing juveniles that this spot is already occupied by a mated pair and that the juvenile should just keep moving on. Individual birds have such consistent hooting patterns that a sonogram, a graphic representation of their sounds, can be used as a ‘fingerprint’. Our bird arrived on the platform around midnight and basically sat, hooted, and nibbled on its rabbit chunk for the rest of the night. Around 5:30 am the owl grabbed its left-overs and took off for the morning.
A juvenile Red-tailed Hawk was sitting peacefully on our platform but after 30 seconds the youngster’s reverie was rudely disturbed by a hot-wheeling, screeching adult! How do we know the second bird is an adult? Juveniles have light-colored eyes and longer tails that aren’t red.
The second bird looks smaller than the juvenile meaning it could be a male. In general, male raptors (owls, hawks, eagles, falcons) are smaller than females. The reasons for reverse sexual dimorphism are not fully understood. Several explanations have been proposed, including
- Larger females are better competitors for territories.
- Competition between males and females is reduced because different size birds hunt different prey.
- Larger females are better at defending the nest against predators.
The past two days a juvenile Red-tailed visited the platform. It appears as if this bird is hunting by the way it bobs its head and intensely stares at the Ceresco Prairie Conservancy. Red-tailed hawks usually hunt from elevated perches like our platform. Hunting must be pretty draining, because the bird took a break to play a quick game of pick up sticks. Play is defined as a behavior that is incomplete and doesn’t serve any apparent immediate function.
Clearly, this bird is not nesting, the breeding season is over, so perhaps we can legitimately call it ‘play’. Apparently Red-tailed Hawks really like sticks. Others have observed them repeatedly dropping and catching sticks in mid-air.
September 17, 2020
Our Great Horned Owl returned this week for some open air dining. That night’s menu consisted of rabbit hindquarters, a slow food meal that began around 8:20 pm, followed by some hooting around midnight, and a brief interlude at an unknown location between 5-5:30 am. The meal was finished off and the owl cleaned itself up with bill-wiping and preening. Before sunrise, it gave a final hoot and the left to spend the daytime hours resting and digesting.
Great horned owls primarily feast on mammals, and rabbits are a clear favorite. In the midwest, rabbits are 54% of their diet. Although an owl can carry up to 1.5x their own body weight, they will tear their prey into manageable pieces and carry them off to a safe place to eat, which explains why we can only see half a rabbit in these videos. Lucky for us, this owl clearly thinks this nest platform is an excellent feeding location!
A juvenile red-tailed hawk has been visiting the platform this week. You can tell it is a juvenile by its tail feathers. Unlike adults, who sport solid rust-colored tail feathers, juvenile tail’s are browner and striped. Juveniles have longer tails than adults, which function like training wheels, providing extra lift as they master flying.
August 19, 2020
A Great Horned Owl has taken a fancy to our platform transforming the unused osprey nest into a banquet table! The past few nights (August 14, 15, 16) it perched on the platform about thirty minutes after sunset. On Saturday night, the owl brought its prey, maybe a rabbit, to the platform. Almost an hour later, after clearing out its tubes, the meal began and continued for the rest of the night. Around 2am, the bird upchucked a pellet, a mass of indigestible bones, fur and claws. By 3am, Sunday morning, the meal was finished. This morning, our platform visitor spent a few minutes surveying the Ceresco Conservancy before going undercover for the rest of the day.
We had a strange visitor to the next platform between 1-3 am. We think it must be a large bird, probably an owl, which sat on the platform out of the view of the camera, and was obviously perched on top of the camera for a little while too.
This morning we headed out to Green Lake to band three 36 day old Osprey nestlings on a private property on Horner Road. Last year, this pair had tried nesting on top of a powerline pole, only to lose their nest and eggs during a severe summer storm. Alliant Energy installed a platform next to the ill-fated location and the pair immediately started rebuilding but it was too late in the season to successfully complete a nesting cycle. Birds returned this spring and we met their little ones this morning. Osprey eggs hatch asynchronously, sometimes days apart because the female starts incubating when the first egg is laid. This results in youngsters that are different sizes. At this platform the largest bird was 1355 g and the smallest was 1165 g, and still had lots of downy feathers.
Our second nest was a bit more exciting, with two older birds that were large (~1800 g), quite alert and active. When we arrived at the K Marsh site, the female was on the platform tearing into a fish. She took off and flew around with it until we returned her young to the platform.
I am so thankful for Alliant Energy’s commitment to supporting our local wildlife and the private landowners who allowed us to access their property to band these birds.
Last week, I planned to band nestlings at two osprey nest platforms in Green Lake County. The banding was postponed because the ground was too soft after the major rains the day before.
Unfortunately, the platform located at the Green Lake baseball field failed. I found the nestling on the ground at the base of the pole. This was surprising because I have been banding at this platform since 2014. Osprey nests fail for a variety of reasons. My hunch is that we have a different pair than last year. Young pairs may have trouble raising young because they may not be able to find enough food for themselves and their young. Poor weather conditions may also play a role. Other osprey platforms in the area are doing quite well, which means that there is plenty of food available for birds that have the right hunting skills. I will be banding a different platform tomorrow which has three nestlings that are just about 5 weeks old. Usually we invite the public but with COVID 19 we will avoid creating a large gathering and just post pictures on the website tomorrow.
After many days with no activity, osprey returned to the platform. All spring we have seen evidence of a pair showing interest in the platform and even lining the nest with soft grass. However, the nest never progressed to the egg stage. The last time we recorded an osprey visit the platform was on June 5. We think this may be a young osprey pair and have high hopes that next year they will return and start a family.
Throughout the month of May, the osprey visited the platform, but nest building behavior had ceased. Male osprey may perform ‘fish-flights’ in which they fly above the nest site carrying fish or nesting material. Our camera couldn’t record this behavior, but the male was observed bringing fish to the platform several times.
Osprey are faithful to their mating partner and nest site, with some sites being used for up to 20 years. Males typically locate a nesting site and place initial nesting material on the platform. If they can attract a female, she will complete building the nest. These birds started building their nest in earnest on April 6th.
Osprey arrived at our nest platform on April 3. Osprey are a migratory raptor that return to Wisconsin in mid-April. Ospreys nest near locations with water and abundant supply of fish because their primary food source is fish. They build their nests in forks of trees, rocky outcrops, utility poles, artificial platforms or offshore islets. Nests are built with sticks, driftwood, seaweed, or turf. Nests are large, being 2 meters wide and 297 pounds! The likelihood that Osprey will nest in our platform is high, especially since they initially started building on the light pole two years ago, and have expressed interest in the platform already.
Bluebird: 27 December 2020
Bluebird sightings are still occurring in the area. The Messitte birds are regularly photo-trapped at all three of our cameras. The young male is just shy of 6 months old and was seen visiting the osprey platform. A few minutes later, an unbanded male was seen on the platform.
Action at the bird cams has been slow this week. No bluebirds have landed on the osprey platform and fewer bluebirds are frequenting the mealworm feeders. In late October, during peak migration in our region of Wisconsin, we were seeing 4-6 different individuals taking mealworms in a single day. Bluebird numbers have dwindled and the individuals that migrate southward are leaving the area. When I enter these resightings into a federal database I get a warning “Species unlikely on this date”.
The cameras don’t lie, and we continue to see a few family groups at the feeders. President Messitte’s birds are so named because they nested in front of his house this past season. From right to left you can see a pair of second year birds, YEPUALDB and her mate, ORALORDG. They are accompanied by their son, ALLBPUYE who is four months old.
November 5, 2020
Bluebirds, like people, have personalities. Let me introduce you to YEALDGYE. This summer he terrorized his nest box monitor, Liz. He dive bombed Liz every single time she checked the nest box and as the weeks wore on she became a little frustrated. Her notes from June 16th stated “Male dive bombed me X8. He is a real jerk!” She even recognized him by his aggressive personality. He switched boxes between nests and she surmised that it was the same bird noting that ‘…the aggression seems similar to the aggression of whoever nested at 49 earlier in the season.” Later we confirmed that it was the same bird because of his leg band colors.
Luckily, not all male bluebirds are as aggressive as YEALDGYE and Liz didn’t have to invest in head protection. The underlying mechanisms for aggressive personalities have yet to be discovered, but not for lack of trying. Researchers studying aggressive personalities in the closely related Western Bluebird determined that it can’t be explained by raging testosterone during the breeding season, so the search for a mechanism continues.
Technology is our friend! Our three wildlife cameras have documented several bluebirds from the trail, like the bluebird ‘attacking’ an owl pellet on the nest platform.
Here is a family portrait of bluebirds. WHALYEDB is the father of the other three who are just shy of three months old. He is just over four years old and does not migrate, we photo captured him in the same place right before the polar vortex hit in January 2019.
Research on the Ripon College Bluebird trail uses a method called mark-recapture. All of the birds hatched in our boxes are uniquely marked with three color-bands and one uniquely numbered aluminum band. We recapture birds by resighting them with binoculars or wildlife cameras and noting their unique combination. From these data, we can learn about their movements and annual survival.
October 22, 2020
Fall migration is occurring and the bluebirds are on the move. In our area in Wisconsin, bluebird migration peaks from late September through late October. We have seen many bluebirds on the osprey platform and at neighborhood mealworm feeders. Of course, banded birds are the real treat. Who are they? How far have they moved? Will they stick around all winter? This year we banded close to 200 birds with unique color band combinations. In one case, a family is still hanging out on their breeding territory. Will they decide to migrate or stay in the yard of their mealworm mama? As the winter progresses, come back and visit this blog to find out.
Banded bluebird fledglings from YEALYEOR’s second brood have been visiting the osprey platform at dusk (August 15, 17, 18). These birds are about 70 days old and have been out of the nest for over a month. They are simply adorable as they explore the sticks and nestle under the overhang of the big sticks. On the video, you can hear them softly singing, tu-a-wees, a contact call between family members. Are they discussing where to spend the night?
We banded the final nest of the season, YEALYEOR’s third brood of four chicks today. Liz, Cormac, and Erika have been monitoring the nest boxes on the RCBT for the past 4 months. I am told that weekly nest box monitoring provided some much needed outdoor sanity during a summer of Covid craziness.
This week the third brood (and fourth nesting attempt) of YEALYEOR hatched. Already this season she has laid 15 eggs and fledged 9 young. In the next three weeks, these nestlings will grow in size from 2 grams at hatch to 30 grams when they are fully feathered and fly from the nest box.
House Wrens occupied about 25% of the trail, bluebirds accounted for another 19%, the last Tree Swallow nest fledged its young, and a few House Sparrows are continuing to nest. Many boxes have been empty for four weeks in a row, so we have started to take them ‘off-line’ by rigging the doors open so House Sparrows and mammals don’t move in over the winter.
This week was exciting because we saw a male (WHALYEDB) who had been banded in 2016 by the college baseball field, observed overwintering in 2018 and 2019 on Thorne Street, and breeding next to Kemper Hall. This guy doesn’t move around much, he is breeding at exactly the same box as last year but with a different female. Since hatching, we have only observed him within 370 m of his first home.
The Ripon College Bluebird Trail is increasingly empty. About 45% of our boxes had no activity this week. Competition between the bluebirds and wrens is reaching a peak as we observe, just like Tennyson, ‘nature red in tooth and claw’. Several monitors have seen eggs disappear from nests and the addition of thick sticks, indicating a violent take-over. At the base of these boxes, they find eggs pierced by a wren’s sharp bill and callously thrown out to make room for the wren’s nesting attempt. Despite this drama, YEALYEOR has laid an additional 4 eggs to start her third brood of the season. We caught up with her yesterday at her box in front of the Wilmore Center on Union Street. She is a fan of mealworms and we supplement each box with a small snack whenever we make a check. Once the bluebirds learn that we are mealworm-mommas, they are quick to land on the box and look for their snack. This allows us to easily identify the
birds whenever we visit.
On the RCBT, bluebirds remain in the lead, occupying over 30% of the trail. Two nests are likely third broods, which means they have successfully fledged two nests and have moved onto a third nest! In Canada, bluebirds stop breeding after the first brood is fledged. In contrast, 12% of bluebirds in South Carolina attempt third broods. In our study population, third broods were not observed in the first 8 years of the study. However, third broods have become an annual occurrence since 2016. The South Carolina population is non-migratory, and the pairs that are attempting third broods were both observed this past winter munching on mealworms on Thorne Street, suggesting that they are behaving like non-migratory birds.
One bird, YEALYEOR, has clearly been staying in Ripon all-year round. Her name represents the color bands on her legs. She has two bands on her right leg (yellow and an aluminum band) and two bands on her left (yellow and orange). She was banded as a nestling in 2016 about a half kilometer from where she breeds each year. We know she spends her winters munching mealworms because we have caught her on camera in both 2018-2019 and 2019-2020. This year, she has already fledged nine young. I will let you know next week, if she has started her third nest.