Tuesday, July 11, 2017

Great Gull Island: Part 2, TERNS!

When Great Gull Island was purchased by the American Museum of Natural History in 1949, it intended to restore the historic landscape of the island. This included its ecology, specifically its nesting seabird colonies.

The birds occupying the island for nesting are Common Terns and Roseate Terns. It is one of the largest colonies for these birds, which is great for the endangered Roseate terns. Let's meet the stars of the island...
Common terns like this one patrolled the walkways, ready to give you a piece of their mind. Very vocal, sometimes they just held their ground and yelled at you as you walked by-- this was the best case scenario.

Outside the door to our room were these little common tern chicks!

Common tern chicks are beggars, when they are hungry, they will beg to any adult passing overhead, especially those with a fish in their beak!

The young terns varied in size, these birds being on the larger side. the young are quite mobile from just a day after hatching.

Clutch sizes also varied in size, from one to sometimes three chicks! A few nests even had 4 or 5 eggs.

So, common tern versus roseate terns... This is a common tern, mature adult.
Their orange beaks seem thicker or heavier than the roseate and also show more orange. The Common tern wing tips are darker, backs are more grey, and tails shorter -- tails and wing tips ended at about the same distance.

A roseate tern. Their bills on the breeding adults are darker, blacker and seem more slender. Their backs are lighter grey- in flight almost looking completely white. At rest, their tails are longer than their wingtips.
Roseates in the right light have a rose/blush-hue to their bellies, giving them their name. Its very subtle, but when you catch it, its beautiful!

Commons and roseates also differ in their nesting preferences. Commons nest on the ground, among the outskirts of the vegetation or on bare ground, they also lay their eggs right on the rocky beaches. While roseate terns nest in rock crevices or terraces made along the hill sides, giving them a human-made nest site.

From the big blind above the dock, we enjoyed views of the birds coming in with fish, having rest from their nests, and taking a chance to preen.

Some birds showed variation in plumage, this one a younger bird or perhaps just coming out of breeding plumage. The time were were at the island was past peak, most nests have been made and birds paired up, raising half grown chicks.

Always a flurry of activity, all around. Babies being fed, siblings stealing food, adults defending their chicks who are trying to eat.  
A gorgeous view of the Roseate tern. This birds numbers were decreased from the plume and feather trade. Birds hunted just for their feathers for fashion-- one of the reasons the Migratory Bird Treaty Act was put together, as many birds some of which common today, nearly went extinct!
Great Gull Island is the largest colony of roseate tern in NY and a large percentage of NY birds nest there.

Roseates are also smaller than common terns, their voices differ too. The roseate having a higher pitch and squeaky quality while the common terns are more robust in their calls, in comparison.

This is why walking around the island is terrifying. I feared every step I took. One had to keep a careful eye on where their foot was about to land as chicks AND eggs are well camouflaged.

...but man, they make even the coldest hearts melt! This young chick has a sibling that is pipping, a small hole signals another chick is breaking out into the world.
Eggs are not a closed system, they breathe and at later stages, especially before hatching a chick will even vocalize from within the egg.

One of the adult common terns who made their nest on a grassy patch right outside of headquarters.

A large clutch- we learned sometimes terns will "dump" eggs in another terns nest. A behavior that is not just limited to cuckoos, cowbirds, and other "nest parasites!" Apparently this is quite common among shore birds and sea birds.

Tail longer than wings? Check.
Almost fully black bill? Check.
Blush hue on chest? Check.
Lighter grey, almost white back? Check.
Smaller in size? Check.

It's a roseate tern!

A roseate with a popular fish that the terns feast on, the sand lance.

One of two chicks lets its parent know that it's hungry!

So many mouths to feed! Good news is we saw a lot of fish coming in, from the popular sand lance, to butter fish, even identified blue fish and a rock eel! It felt like there were enough fish to go around, even much so that the adults even throw them at you as you walk through their colony.

A chick doing its best impression of a rock.

But seriously, their camouflage is almost too good!

A not uncommon common tern chick sight. Little beggar.

A lot of folks may have never noticed terns, brushing them off as a black, white, and grey "seagull." A closer look reveals thinner, pointed wings, a less chunky body, and a long pointed, and often forked tail.

Our focus was mainly on the common terns, and they are just more abundant in general on the island. There are close to 10,000 pairs of common terns on GGI. At the time we were there we were at over 8,000 pairs. Birds are still laying down nests, but the peak of nest laying is past.

A family life that at times seems not too far off from our own...

Some chicks, affectionately referred to as "elephants," or "ellies," for their large size, grey color and ability to run! Elephants have their down feathers slowly replaced with the adult feathers- ones better suited for flight and life over the water.
Birds with such feathers coming in often stretched and flapped theirs wings, getting their exercise in preparation for flight.

A common tern shows off its sand lance.

Those bright gapes are common in all young birds- a signal for parents on where to put the food! With age the common terns mouth inside will match the orange of the outside, losing that contrasting fuchsia and orange target for fish to be placed.

Wing stretching by one of 2 siblings, showing off that transition from downy chick to a juvenile bird.

One thing I was amazed by was the variety of calls the common terns made. Since I often heard them outside our door they had sounds that were specifically for their chicks, sounds used towards neighbors getting too close, the warning "clicks," made as they approached you quickly for a dive-bomb, to even whimpers when you caught them for processing and measuring. Sometimes I heard a sound and realized it came from a tern, not expecting to hear some of the sounds they made.

This tern is sitting atop a blind, where humans can hide and use the small look out holes to make observations from. You crawled in up a ladder, treehouse style to a platform.

The beautiful roseate, with that rose-colored belly. You can see the whiter, lighter wing tips and overall lightness of this bird compared to the commons below.

During one of our "swim breaks," where it was too cold to swim, I sat and tried getting birds in flight, in over cast skies, which was not easy. Birds were flying in overhead with beaks of fish, which is a great thing to see as it is promising for more chicks to survive. This bird has a sand lance.

We also saw quite a few little bluefish come in- as birds often dropped them and we could retrieve the fish to identify. In terms of having the colony thrive on GGI it is also important to have a thriving population of food. Some birds fly to block island and other not super close places to hunt. We know this from the birds equipped with tags that are picked up by receiving towers on surrounding islands and areas.

A sub-adult common tern.

Being immersed in the colony, I gained a huge respect for these birds, seeing their drive to raise the next generation to seeing the ugly, the birds attacking young of conspecifics and even killing other nearby birds. They truly are little dinosaurs!
While lying in my bunk at night, these birds continue through the night, their voices constant. Part of me did feel like there were little compsognathus outside our room at times - with no TV and detachment from reliable internet service, your mind can wander and let your imagination take over. I liked the idea of being on this island, surrounded by feathered dinosaurs.