Coastal Watch, Part 6 - Robber Gulls

Herring gull

When it comes to harvesting the sea, there's them that gets and them that gets from them that gets. I'm just reporting what I see.

Common loon

When I see a sea gull sitting on the surface there's a good chance it has a diving bird under surveillance, resting close by or plying the deep waters for food.

King eider, first year drake

The gull only stations itself near birds that bring their prey to the surface for consuming. Divers able to swallow their food under water are of little interest to gulls.

Common eider, female

The gull has to be quick to snatch a morsel before its first proprietor can swallow it.

Common eider, male

Patience and swiftness pay off for this gull with a starfish from the ocean bottom, stolen from a hapless eider.

The eider shrugs of its loss and prepares to dive again.

White-winged scoter, male

Another day, another gull keeps vigil on a group of scoters that have abilities very different from its own.

Hunger sends a scoter down in search of a meal. It opens its wings and tail feathers to help its movements. Remarkably it doesn't get wet to the skin.

The successful scoter is met at the surface by the successful gull.

Coastal Watch, Part 5 - Birds at Rest

Purple sandpipers at tideline

In midwinter as the tide drops below its midline you may come across Purple sandpipers foraging in the Irish moss and dashing down between receding waves. Small flocks of them go winging off suddenly for undisclosed reasons. When the ocean reclaims the intertidal zone the birds go off to rest.

Far down the shore in the direction I'm walking I notice an incongruous bump on the silhouette of a boulder. It hasn't moved during my approach, even as I set up the camera on a tripod.

Purple sandpiper resting

A sandpiper has tucked itself into a fluffy ball. Its eyes flutter open and closed every few seconds. Is my intrusion keeping the bird awake? Exposed as it is, vigilant watching for merlins and peregrine falcons seems prudent. Those eyes should never close too long.

Sanderlings

At rest a sandpiper economizes energy by bringing one leg up to its body and turning its bill back within its wings.

Mallards

Mallards in a similar posture can close both eyes. They feel more secure snoozing among nearby ducks that stay alert for danger.

Horned grebes

Grebes sleep with their plumage fluffed for insulation and their bills tucked forward beneath chest feathers.

Harlequin ducks

Harlequin ducks roost periodically outside the tumultuous surf where they spend most of the day. Some this group have at least one eye closed. It's possible they sleep uni-hemispherically, that is, resting half their brain at a time. Ornithological researchers have proven that some birds are able to do this on long flights while the other half of the brain navigates and maintains watch.

Coastal Watch, Part 4 - Drinking Water at Sea

An intriguing variety of marine vertebrate animals maintain a salt level in their blood that is similar to ours but only a third that of the surrounding sea. All of them need to replace water lost daily from their bodies, as in the exhalations of this Minke whale. How are they able to do something that we cannot?

Minke whale off Halibut Point

Nearly all marine mammals subsist on fish and other organisms with similar salt levels to their own. They gain most if not all the 'fresh' water they need from their prey without taking in excess salt. However they are generally equipped with kidneys much larger and more efficient than our own to filter out harmful salt that reaches their blood through swallowing or digestion.

Mammals constitute the only class of vertebrates in which the kidney is always the major organ of osmoregulation. * While we lack full agreement among scientists it appears that whales can at least occasionally drink from the sea to maintain their necessary physiologic balance. As in humans, but much more efficiently, excess salt is eliminated from their bloodstream in highly concentrated urine. ¹

Red-breasted merganser and horned grebe

Birds that spend much of their lives on the ocean have a similar challenge in meeting their fresh water needs. Fish eaters such as mergansers and grebes do obtain from their prey water of tolerable salt content.

Iceland gull

Some oceanic birds like gulls visit land at least occasionally to drink fresh water from terrestrial sources.

Northern gannet

Others like the gannet never intentionally come to land except in their breeding season.

Dovekie

Pelagic birds like the dovekie spend most of their time far from any shore and the possibility of drinking fresh water.

Common loon

Birds have a reptilian type of kidney considerably less efficient than a mammalian kidney at concentrating and secreting salt. If they drink sea water they must have some other means for eliminating excess salt from their bloodstream.

King eider

This problem is especially critical for birds like eiders that subsist on mollusks or invertebrates which, unlike fish, are in osmotic equilibrium with sea water. Their food sources are salty.

The salt gland in an albatross ²

All birds (except passerines, according to one source) have a salt-secreting nasal gland, but in terrestrial species it is very small. The size of the gland in marine birds is 10 to 100 times as large. Its size varies at least in part with the degree of exposure to salt in the species' ecology.
 

A large order of seabirds like the albatross illustrated above has developed tubed nostrils to increase their salt discharging capability. Within this group called the Procellariiformes  are some occasionally seen from shore at Halibut Point, like shearwaters, storm-petrels, and fulmars.
 

Great black-backed gull

Comparative physiologist Knut Schmidt-Nielsen studied the functions of salt glands in great black-backed gulls. In one experiment, a gull ingested about 1/10 of its body mass in seawater (the equivalent of a 150-pound human drinking about 2 gallons of seawater, more than a lethal amount). After three hours, the bird had totally eliminated the salt load, mostly via excretions from its salt glands (which were 10 times higher than salt elimination from its kidneys). ²

 

Razorbill

With this remarkable adaptation oceanic birds have been able to establish themselves far out to sea for most of their lifetime.

* Osmoregulation is the maintenance by an organism of an internal balance between water and dissolved materials regardless of environmental conditions. In many marine organisms osmosis (the passage of solvent through a semipermeable membrane) occurs without any need for regulatory mechanisms because the cells have the same osmotic pressure as the sea. Other organisms [including vertebrates such as mammals and birds], however, must actively take on, conserve, or excrete water or salts in order to maintain their internal water-mineral content.

Courtesy of Britannica.com
 

Sources

1. Knut Schmidt-Nielsen, "The Salt-Secreting Gland of Marine Birds,"  Journal of the American Heart Association, May 1960.

2. "Why Can Some Birds Drink Salty Seawater?" Living Bird magazine, Summer 2017.

 

 

 

Coastal Watch, Part 3 - Winter Shorebirds

On a winter outing to Halibut Point you might encounter little shorebirds wading along the water's edge or scrambling over mossy rocks at low tide. They will most likely be one of the two species here at this time of year. Their perky animation in this vast and challenging environment sets a fine tone for two-legged creatures on the edge of comfort.

Purple sandpipers

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sanderlings

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2020 Vision

Seldom does a New Year arrive so boisterously. 

When confronted with sleepless nights Wendell Berry wrote of going to the woods. He concluded his poem "The Peace of Wild Things" with a ready remedy: 

I come into the peace of wild things
who do not tax their lives with forethought
of grief. I come into the presence of still water.
And I feel above me the day-blind stars
waiting with their light. For a time
I rest in the grace of the world, and am free.

At Halibut Point we start the New Year with gratitude for its natural beauty and for the preservation work of its custodians, the Commonwealth of Massachusetts and The Trustees of Reservations.