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Posts Tagged ‘Beach’

While walking through Ship Island’s colony, I’m always fascinated by the variety of egg shapes and sizes we come across. Out of curiosity, I decided to measure and photograph some of these eggs to see how variable Common Tern eggs can be!

Eggs are developed rather quickly. After copulation, an egg can form and be laid in 24 hours! Typically, an egg can be added to the nest every 1 to 2 days. While most clutches contain 1-3 eggs, this season, we’ve found some with 4 to 5! The nest starts off as a simple scrape in the sand, gravel, or dirt. As parents spend more time around or in the nest, they’ll move twigs, vegetation, seaweed, and other objects around to create a proper nest that will keep their eggs inside.

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A Common Tern nest with 3 eggs

On average, Common Tern eggs are 42 mm long and 30 mm wide. As always, there are some eggs that do not meet these parameters. I found that lengths vary the most, ranging from 38 to 46 mm! Meanwhile, egg widths stay closer to the average, varying from 28 to 31 mm.

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These two differently sized eggs are from the same nest!

Tern eggs are subelliptical meaning they are elongated with tapered rounded ends. The widest point of the egg is off center. Like size, shape varies greatly! Some eggs have the widest point towards the middle, creating an oval shape. Others have the widest point so close to one end, the egg has a long narrow point, like a raindrop.

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A typical, subellipitcal egg

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Almost an oval-shaped egg

Sometimes, the most striking feature about the egg is its color and pattern. In just one clutch, the eggs can look wildly different. The colors can range from cream, tan, light brown, to dark brown. The shells are covered in small to large dark splotches and streaks. These markings can concentrate around the widest point, like a belt, or spread across the egg like freckles. The color and pattern is thought to help camouflage the eggs on the beach. However, we occasionally find some odd eggs that stand out. Some appear almost pure white with faint or no markings at all! Others are so dark brown that the markings are hard to distinguish.

Although Andy and I love finding these eggs, we’re hoping that they’ll be hatching soon! While there are some eggs which have been freshly laid, there are some which have survived abandonment and could be hatching any day. We look forward to welcoming the first chicks to Ship!

Percy

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This weekend the Ship Island crew headed over to Pond Island to take part in a beach cleanup along the shore. Morgan and I, as well as several other volunteers, collected dozens of trash bags filled with lost buoys, cans, bottles, and more. This year is the first year the group will be able to actually recycle the plastic that was collected. Through the company, TerraCycle, our collection of plastics, no matter how dirty or broken they may seem, will be sent over to be thoroughly cleaned and re-purposed. Typically, most objects made out of recycled plastic only consist of about 30% reused material. Though it doesn’t seem like a lot, or maybe even not enough, if the concentration is increased then the new object becomes closer to the end of its lifespan and can no longer be reused. It was good to get off the island and spend some time with others working to keep our environment clean, but we’re glad to be back on Ship with our terns!

 

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Section of a boat that was found washed to shore. We needed all hands on deck to carry this one over!

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Beach Cleanup Volunteers

Back home on Ship, we’ve had problems with other birds predating on our Common Terns and their eggs. Currently, Great Black-backed Gulls, Herring Gulls, American Crows, Peregrine Falcons, and Northern Harriers are our main concerns. Almost every day we spend two hour shifts in the blinds to observe the tern behavior and keep an eye out for any of these predators that might pass by. During the evening we’ve been marking nests with predation sticks so we can notice if any eggs have gone missing. By doing this we are also able to get a good idea on how many terns we really have on the island. It doesn’t look like it, but so far we have counted over 500 nests, which means we have over 1000 terns! So far so good! In a few days we will be doing a GOMSWG census which will give us an even closer estimate on our tern population size. We’re excited to share the results with you next week!

-Amanda

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