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Posts Tagged ‘Tern chick’

It has already been over two weeks since the Great Horned Owl roamed the surface of Ship Island looking for a late-night snack. You would think that over time, the terns would settle down and begin to behave “normally.” But that’s not the response we’re seeing. Even today most of the colony begins to sweep high above the island soon after sunset, then disappear quietly out over the ocean. It seems that small numbers do come back to warm their chicks and eggs, but the majority aren’t seen again until sunrise.

The owl caused full colony abandonment during the nights on the island. This occurred for over a week straight, which might have led to some long-term effects on chick physiology. Many of the eggs didn’t end up hatching since they weren’t incubated during the nights. But, some eggs were still able to make it. Typically, eggs hatch after 21-23 days of incubation. With the owl disturbance, incubation length increased, which is why our chicks arrived slightly behind schedule.

Although we have many healthy chicks all around the island, there are a select few that are showing what we assume to be the negative consequences of this over-exposure to the cold and wet nights on a Maine island. When terns incubate, they are constantly rotating the eggs around. This allows for even nutrient and heat distribution throughout the egg as well prevents the embryo from sticking to the shell, allowing it to float in the middle and develop successfully. Without this constant rotation, it’s possible that the chicks could have developed certain physical defects.

 

Not only are we seeing odd chick appearances, but we are also seeing a huge change in colony behavior. The terns have been extremely sensitive to any presence that might seem or sound threatening. This even includes species that are not considered predators. In order to protect themselves, terns often mob, dive-bomb, or attack the predator. They also might flee, just as they did with the owl. Their actions depend on the level they feel threatened themselves versus how threatened their young are. We’ve observed terns going after Common Eiders, Dowitchers, and Harbor Seals. They were even frightened by the sound of a nearby fishing boat. Although we can see that these species are here to do no harm, it’s still good to see the terns working hard and being extra protective.

These actions displayed by the tern colony isn’t uncommon among populations who are or were at risk of nocturnal predation. In fact, it has been witnessed in several other Common Tern studies where owls were present. Looking at a well-known colony observed by Monomoy NWR in particular, you can read how they experienced very similar results years ago (Nisbet and Welton, 1984).

It’s amazing how a single bird can influence an entire colony in only a few days. This owl left an impression on the terns to last the entire season. The fate of this years fledgling was greatly altered and we can only hope that next year the colony works to make up for this years loss.

On a better note, we’re still waking up to a few more chicks every day, and we’ve already seen a few fledge! Based off of our provisioning efforts and weight measurements, our current chicks are growing at a steady rate and being fed a healthy diet, which mostly consists of Atlantic Herring. Some chicks are being fed so much that they actually have to lose weight in order to lift themselves off the ground and fly! We’re glad to finally start seeing our chicks transform into successful adults!

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One of my healthy provisioning chicks. Not quite ready to fledge yet!

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Chicks that were recently born. Only a couple days old!

Only one more week until the island closes. This season really flew by! I’ll keep you updated on any more unusual or exciting events happening on Ship!

-Amanda

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This past week on Ship Morgan and I both took our short breaks off the island. While Morgan was away I was joined by Kelby from PMI to work on predator control, productivity plot management, chick banding, and more!

We’re starting to see more and more chicks every day! Usually when we’re checking the productivity plots we can see when they start pipping. This is when their little beaks start to break open the egg. This lets us know that the next day we will definitely have some new arrivals to weigh and band if they’re dry and ready.

Before we start provisioning, we still have some time to re-sight birds from previous years. Typically, they will have a small silver BBL band on their ankle which contains either 8 or 9 numbers. We can use a spotting scope to see these numbers and enter them into a database where we can learn more information about that bird, such as it’s age. To make re-sighting easier, we put up posts for them to perch on so they aren’t being covered by the vegetation and are closer for us to see. While I was re-sighting from the blind, I spotted a tern that hasn’t been re-sighted in 19 years! I also found one with an orange band. This means that it was banded all the way in Argentina, which I thought was pretty cool.

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An example of a BBL band that can be found on the leg of a Common Tern. As you can see they are very small, which makes them difficult to read.

Now that the owl is gone, we are starting to see more birds come back to the colony. Many of them left during the time he was here and abandoned their nests. Thankfully now they’re starting to scrape the ground and re-nest. Chick age distribution around the island will surely be scattered, but at least they’re not giving up!

Now that I’m back on the island, there’s a lot more chicks running around and much more work to do!

-Amanda

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So far around the island we’ve come across Common Eider, Mallard, Savannah Sparrow, and Spotted Sandpiper chicks. Although a little behind schedule, we were beyond happy to finally find our first Common Tern chicks! Soon we will start banding them and taking measurements. Hopefully we will start seeing more every day!

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Our first Common Tern chick!

Our terns have been acting different than normal. Rather than settling down to incubate, many of them appear to be much more active flying around and leaving the island. We grew suspicious that there might be an owl around. In order to make sure it doesn’t disturb our terns, we set up a total of 17 foothold traps covering all sections of the island. When we placed the traps, we put them in areas that seemed suitable for an owl to land. If the owl lands on the platform that contains the trap, its leg will be caught. This trap doesn’t hurt the owl because it’s padded, but it allows us to capture it so it can be relocated. Though our minds were focused on an owl, we didn’t forget about our frequent Peregrine Falcon visitors. To prevent any unintended capture, we made sure to set off the traps during the day.

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The sign is lined with chicken wire at the top making the post with the trap the only suitable place to land

Only a few days after setting the traps, we caught the owl! Morgan and I noticed the terns were once again acting strange during our night stint, where we took shifts watching the colony between 6:00 PM and 12:00 AM. The next morning the terns were dive-bombing at the ground, and I could see through my binoculars that the trap wasn’t on the post anymore. It seemed unlikely that we caught an owl, especially since we weren’t completely sure we even had one, and last year it took over 2 weeks to catch it! We walked over expecting to find something like a gull caught up in our trap, but to our surprise it was a Great Horned Owl! We safely caught the owl, covering its head so it would stay calm, and removed him from the trap. It already had a band on its leg, so we suspect that it might be the same one from last year. The owl will be brought to a rehabilitation center to make sure it isn’t hurt, and it will be released somewhere far from our terns! We are so thankful we caught it in time, especially now that our eggs are hatching!

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Morgan about to cover the infamous Great Horned Owl with a blanket to keep him calm

 

Outside of bird research, we enjoy watching the Harbor Seals bask in the sun and swim around with their pups. The seals can be found on two adjacent islands. One pup decided to visit us on Ship this week. We were nervous when we didn’t see the mom around, but we were taught that after 3 weeks the pups begin to live on their own.

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Curious pup visiting our island

Ship has been very busy this week. We’re hoping to continue to wake up to new surprises every day, but only good ones!

-Amanda

 

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Photo by Wayne MacCabe

Photo by Wayne MacCabe

This is the Captain, who lives on the walkway in front of the house. What makes him so special to us is he was rescued from freezing rain when he was still inside his egg. One rainy day the area where Captain’s nest was got flooded with collecting rain water. The whole nest and the three eggs inside it were completely submerged in the water and were floating around. The parent was hovering over the nest, unsure of what to do. After seeing this I quickly ran outside and scooped up the nest and re-located it to a nearby high-elevated area. Seconds later Captain’s mother was back on her nest. I was relieved to see this because terns can be sensitive to any slight change to their nest and can be spooked away if they feel something is wrong. Unfortunately, I still didn’t have high hopes for the chick’s survival. I didn’t know how long the eggs were floating in the cold water, they could have passed away from the cold temperatures or from the water sealing up the pores on the egg which lets the chicks breath oxygen from the air. But, to my surprise about a week later Captain hatched and soon after so did his brother, Sailor. I named the chicks this because the nest was floating around like a ship at sea. Now, both Captain and Sailor are fledging!

We have over 2,000 chicks on the island and just our presence here increases the survival rate for these chicks. This is because we deter predators like greater black back gulls, peregrine falcons, herring gulls, and more which will make a quick meal out of the fledging terns and chicks. Realistically, we can not 100 percent stop predation from these species, but we work hard to keep fatality numbers low. Without us working here on the island these birds would likely take over and would have a devastating blow to the tern population. It made me so happy to see that Captain had made it but I noticed I gained a lot more than just satisfaction from seeing him survive, I gained a new understanding of my time here on the island. This event encouraged me because it really showed how my time and work on the island present on the island.

-Laura Bollert

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Tern chicks hatch with 5 o'clock shadow, I think that's what makes them so cute!

I didn't expect to see him as i walked by, I did a double take! The pips in our adjacent productivity plot have tripled overnight. More chicks are on their way!

Right on schedule, found this little bundle of joy right outside one of our productivity plots!  Tern chicks are Semiprecocial.  Their eyes are open, they can stand, and take food within a few hours of hatching.  These young chicks will stay under an incubating adult until food arrives, and quickly return to the warm safety of its parent after food is delivered.  We will be keeping track growth rates and fledging success through an enclosed sample of the population.  As well as the rate and quality of food delivered through a different sample of chicks.  All of this is about to start on islands across the Gulf of Maine stay tuned for more updates from Metinic and Petit Manan! Posts on provisioning, productivity and telemetry are coming soon!

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