Fifty years ago the late Jim Linzell and I were writing our monograph, Salt Glands in Birds and Reptiles, for the Physiological Society; it was published in May 1975. In this series I revisit some of the topics and people who followed up the discovery of salt glands in birds by Knut Schmidt-Nielsen.
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Knowledge of how birds survive at sea can be divided into two eras: Pre-1957 and Post-1957. It was in 1957 that Knut Schmidt-Nielsen (1915-2007), along with his colleagues, Carl Christian Barker Jörgensen and Humio Osaki, who were visiting scientists at Duke University in North Carolina, discovered salt glands. These organs secrete salt at very high concentrations allowing marine birds to get rid of excess salt which they may ingest by drinking seawater and/or by eating invertebrates like squid which contain much more salt than fish.
The kidneys of birds and reptiles, in contrast to those of mammals, simply cannot produce urine with a high salt concentration. Therefore the discovery of an extrarenal route of salt excretion from glands in the head and emptying into the nostrils explained why marine birds could drink water and survive on salt-rich prey containing. Until then there had been no agreement, some observers claiming that not only could such birds drink seawater but also that, in captivity, seawater was essential for their survival.
Few zoos attempted to keep pelagic birds—those that remain far out at sea for months or years. But those that did came to the conclusion that they must be provided with saltwater or with salt added to their food, usually fish. In 1925 Glover Morrill Allen (1879-1942) then recently appointed to lecture in zoology at Harvard, wrote in his book, Birds and Their Attributes of 1925:
Most sea-birds are known to drink salt water in preference to fresh; indeed captive gulls may die without it.
That is why, my previous post on the keeping and failing to keep Waved Albatrosses at Brookfield Zoo, Chicago, in 1935, is interesting. They were fed by hand on freshwater fish dipped into salty water.
However, the work of Schmidt-Nielsen and his colleagues threw no light on why pelagic birds would need salt water in order to live. In all species of birds, including domestic ducks and geese, tested thus far, the salt glands only turn on in response to the ingestion of salt water sufficient to raise the osmolarity of the blood. No salt water: no secretion. Thus pelagic birds should be fine living on fresh water. It was only several months after the full paper by Schmidt-Nielsen and his colleagues was published that this apparent anomaly came to light.
Schmidt-Nielsen’s discovery had actually started in the late 1930s but the war and his move to the USA had delayed his following up his earlier, inconclusive, experiments in Norway. The discovery was followed up by reports from those who had realised they had seen salt gland secretion in actioon, drops of fluid appearing on the end of beaks for example, without appreciating the significance. Others with access to marine birds, followed suit to demonstrate the presence of salt glands in other species.
In January 1958, Hubert and Mable Frings of the Department of Zoology and Entomology at Penn State University were on Midway, that famous island in the Pacific. They worked on sound communication in insects (Hubert had started off as, primarily, an entomologist, and were trying to see if sound could be used in pest control, invertebrate and vertebrate. It would appear they were on Midway because of a contract they had or were about to get with the US Office of Naval Research. The US Navy was very concerned because aircraft and albatrosses have a habit of colliding. In a report of research done between 1959 and 1963, the scale of the problem can be seen:
At Midway Naval Station, 1,100 miles west-northwest of Honolulu, military aircraft collide with flying albatrosses at the rate of about 300 to 400 per year. One aircraft out of every five that hits an albatross on takeoff either aborts (stops before it is airborne), or dumps fuel and returns for appraisal of damage. About 70,000 pairs of Laysan albatrosses [Phoebastria immutabilis] and 7,000 pairs of blackfooted albatrosses [Phoebastria nigripes] nest at Midway in any given year. The population is declining.
The Frings knew of the then very recent discovery of salt glands and took the opportunity to look for any signs of salt glands in action:
The birds were, therefore, observed with this in mind, and it was noted that after fighting among the Black-foots, or occasionally during the ritual dancing, some of the birds showed drops of fluid at the tips of the beaks. Furthermore, during a local harassment campaign, many of the birds in the treated area were actively dripping. This suggested that the gland could be activated by “stress” or excitement.
There was a limit to what could be achieved on Midway and so the US Navy agreed to fly four birds of each of the two species to Pennsylvania. They arrived on 18 April and were housed initially in an old hen house on the university farm. The vicissitudes of getting the birds to swallow the offered food and unsatisfactory housing and water supplies were explained in a full paper in Condor, and here I will only describe some salient points. The Black-footed Albatrosses soon learnt to take food offered by hand. The Laysan did not and until it was found that a piece of fish, for example, could be slid into the beak nearer the mouth and would be swallowed, they declined. Two of the latter died but not of inanition but, it would seem, a lack of salt. Handling and disturbance was seen to result in secretion by the salt glands but the birds drank the fresh water provided. When the two remaining Laysans were declining badly, it was decided to give each an injection of salt. Recovery was remarkably rapid. Within ten minutes the birds were up and walking normally. The Fringses concluded that because salt-gland secretion can be induced by excitement or “stress” in these birds and because they had no opportunity to drink salt water, they became hyponatraemic. They seemed unable to distinguish fresh water from salt water.
These problems were overcome by providing salt in gelatine capsules embedded in the fish used to feed the birds. Later, an artificial sea water pool was provided and the birds were seen drinking from it.
The remaining birds thrived and were moved by air, first in June to the Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, where they were given real sea water in tubs from which they drank. Then, on 20 August 1958, they were sent to the National Zoological Park in Washington, D.C. ‘where Drs. Theodore Reed and Malcolm Davis are continuing with the methods described here’. I do not know what became of the birds after they reached Washington.
Thus Hubert & Mable Frings explained why some marine birds need salt water to drink when in captivity. In the wild any loss of salt evinced by the salt glands switching on seemingly inappropriately would easily be made up from squid in the diet or by drinking sea water.
I will return in a later article to the question of salt-gland secretion appearing or the rate being changed by internal or external stimuli caused other than by an increase in the tonicity of the blood plasma. I will do so with some trepidation since the story ends with a most horrific human tragedy.
The main reason for the birds being caught and flown to Pennsylvania was of course to investigate the salt-gland secretion. This was done while the albatrosses were still at Penn State. For this phase, Hubert Frings enlisted the collaboration of Adam Anthony from the physiology section of the Biology Department (1923-2012) and Martin Warren Schein (1925-1998) who had wide interests in animal behaviour and then in the Poultry Science Department. Their paper was published in Science. When stimulated by supplying salt capsules in the food, the secretion contained between 792 and 856 m-moles of sodium per litre. This concentration of sodium is twice that of sea water.
The concentration of salt-gland secretion compared with sea water is of course the key to understanding the role of the salt gland in marine birds. While it is convenient shorthand to describe the function of the glands as getting rid of excess salt, it would be of no use to the bird if the concentration did not exceed that of sea water. The whole mechanism is there because it enables birds to obtain osmotically-free water. As such it is a highly effective desalination plant that requires some of the highest rates of blood flow ever observed while its cells are stuffed with mitochondria to drive the energetically expensive transport systems across its cell membranes.
Although the rate of secretion was not measured the group assembled by Hubert Frings noted the secretion is discharged from the nasal glands through small openings below each tube-nostril. The fluid then flows along grooves on the beak to drip off the end. After being given a salt load, drops were seen falling at internals of 2-4 seconds.
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| A Northern Royal Albatross (Diomedea sanfordi) at the Royal Albatross Centre, Dunedin, New Zealand I photographed this one through the glass of the hide in 2019. The small openings below the tube-nostrils together with the grooves along the beak can be seen clearly. |
But who were the Fringses who were in the right place and at the right time to embark on a study of the albatross salt gland?
Hubert William Frings was born in Philadelphia on 1 January 1914. His father, born in Germany, was a flooring contractor. Hubert graduated from what became Pennsylvania State University in 1936. He received a Master’s degree from the University of Oklahoma in 1937, and a PhD from the University of Minnesota, in 1940. Teaching jobs, traceable to Iowa and Missouri, can be found in the records. He became an insect physiologist at the US Army’s Chemical Center in Maryland. He taught biology for a short time at Gustavus Adolphus College, Saint Peter, Minnesota in 1946-1947 but then returned to Penn State where he climbed the academic ladder until 1961. Then he went to the University of Hawaii until 1966. Hubert and Mable are commemorated there by an endowed scholarship. Finally, he joined the University of Oklahoma, becoming David Ross Boyd professor until his retirement in 1979.
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| Mable and Hubert Frings on their wedding day, 9 June 1936 (from a family tree on ancestry.com) |
Hubert married Mable Ruth Smith on 9 June 1936. Her family were farmers in Pennsylvania. She was born on 11 April 1912.
Hubert and Mable wrote two books: together: Animal Communication in 1964 and Concepts of Zoology in 1970.
As part of their support from the US Office of Naval Research, Hubert and Mable, together with their son Carl Frederick, published An Annotated Bibliography on North Pacific Albatrosses in 1966.
Mable died on 28 March 1998; Hubert on 8 September 2008, both in New Hampshire.
…Meanwhile on Midway the albatrosses are thriving with over 2 million birds nesting on 2.4 square miles of the atoll. The US Navy left in 1993 and flights to and from Henderson Field only occur at night during the nesting season.
Allen GM. 1925. Birds and Their Attributes. Boston: Marshall Jones.
Frings H, Anthony A, Schein MW. 1958. Salt excretion by the nasal gland of Laysan and black-footed albatrosses. Science 128, 1572.
Frings H, Frings M. 1959. Observations on salt balance and behavior of Laysan and black-footed albatrosses in captivity. Condor 61, 305-14.
Peaker M, Linzell JL. 1975. Salt Glands in Birds and Reptiles. Cambridge: Cambridge University Press.
