As a curator at the AMNH Mayr had only little time for studies on the ecology and breeding biology of birds, although he was able to complete a number of projects (e.g., Mayr 1935e) and to discuss the territory theory in birds (1935c). Also, during the early 1930s, he directed the research of several members of the Linnaean Society of New York who, at his suggestion, investigated the life history of selected bird species in the surroundings of this city (pp. 109-110). In the spring of 1940 Mayr studied several small colonies of Red-winged Blackbird (Agelaius phoeniceus) in northern New Jersey to test an idea that colonies of social birds would start nesting the earlier the larger the colony, also to see to what extent there was polygamy, and how the territory borders change with the seasons. He went out every morning at about 5:00 am and was back home shortly before 8:00 to start the commuting trip to New York. His findings indicated that the small colonies comprising only two or three territories in the small potholes with bushes and trees were established earlier than the larger colonies in the big cattail marsh where the birds had to wait until this year's cattail stalks were tall enough to support the nests. Hence the rule established for sea birds did not apply to these inland colonies (1941l). Mayr also watched birds while crossing the North Atlantic on board a passenger ship (1938h) and visiting the Bahama Islands (1953g), he described anting by a song sparrow (1948f) and gulls feeding on ants (1948g). During the early 1940s he intended to study the nature of behavioral isolating mechanisms in birds experimentally but failed because of logistic difficulties (p. 228).
In the course of his efforts to introduce experimental biology, ecology and ethology into American ornithology, Mayr encouraged Margaret M. Nice (18831974) to write her two-volume monograph of the Song Sparrow, which made her famous. They had met at the annual AOU meeting in Detroit (October 1931): "Thus started a warm and enduring friendship that became exceedingly important to me," she wrote in her autobiography (Nice 1979: 109). Mayr was delighted to find an American "interested in more than faunistic records and pretty pictures" and started her reading the German Journal für Ornithologie. Mrs. Nice lived in Columbus, Ohio where she had no chance to discuss her studies with other naturalists for she was excluded from the strictly masculine Wheaton Club. Mayr was present when, on his suggestion, she visited Berlin and the Museum of Natural History for ten days during the summer of 1932. Stresemann, similarly impressed with her work, published a detailed progress report in German in Journal für Ornithologie (1933/34). Mayr considered her Song Sparrow monograph "the finest piece of life-history work ever done." As the editor, he offered to publish the final manuscript in the Transactions of the Linnaean Society of New York (1937, 1943). He also persuaded N. Tinbergen to send him his observations of the Snow Bunting in spring for publication. At the AMNH Mayr established a seminar for birdwatchers in the New York area (p. 109) and cooperated closely with G. K. Noble (1894-1940) who pioneered in behavioral experiments with free-living birds and other vertebrates (Mayr 1990h). Noble's sudden death was particularly shocking because he was such a vital person, but died within three days by a throat infection. Similarly, Ernst Mayr encouraged and influenced the work of David Lack, Konrad Lorenz and Niko Tinbergen in Europe, as pointed out by Burkhardt (1992: 300, 1994:360). The Austrian ethologist Lorenz worked in Germany during most of his career. He supported Mayr's lifelong interest in animal behavior. In fact, about half of Mayr's PhD students did their theses in behavior rather than either evolution or systematics (p. 262). Mayr wrote in his autobiographical notes:
"In 1951, Gretel and I visited the Lorenz's at Buldern, Westphalia. There we had very long discussions, even controversies. At this period, Lorenz always talked about the Greylag Goose in a strictly typological sense. By contrast, I insisted that every Greylag Goose was different from any other one. 'If a Greylag Goose becomes widowed,' he said, 'he or she will never marry again.' I asked him on how many cases his statement was based, but he had only a vague answer. At any rate my insistence that every goose should be treated as an individual eventually resulted in Lorenz hiring a special assistant to keep track of the activities of every single individual in the flock. Each goose had its own card in the cardfile and all about each goose was recorded daily. Needless to say, within the first year he already had one or two cases of widowed geese remarrying. Many other sweeping statements about the Greylag Goose were likewise refuted by individual records. [...]
When Lorenz went to Seewiesen [in 1956] I visited him several times and gave seminars to his investigators. Our friendship, of course, continued after his retirement  when Gretel and I visited the Lorenz's at Altenberg, Austria. With part of the money for his Nobel Prize Konrad had built a very large seawater aquarium with the most wonderful coral reef fishes. There he went after breakfast with me and we sat on a comfortable bench facing the aquarium. He told me exactly what every fish would be doing the next minute, and what this meant, and quite obviously he had an amazing understanding of the psychology and social behavior of these fishes. What bothered me was that he never kept a note. When he looked at the fishes it was mainly for aesthetic satisfaction.
Lorenz was a born naturalist and observer who was able to see things that no one else notices. He could look at a group of displaying ducks and find some details in their courtship that others, who also saw the ducks, never saw. There is a wonderful story of Lorenz missing a class he was teaching at the University of Münster during the early 1950s." When he was staying at castle Buldern with a large park, he went by motorcycle to reach the university. One day he left at the usual time. After quite a while, his assistant called up Mrs. Lorenz and said that Dr. Lorenz had not appeared and asked what was the matter. She said he left at the usual time. He must have had a motorcycle accident. So the assistant said he'd jump on his bicycle and she should jump on hers and they would meet. She hadn't left the park when she saw the motorcycle lying on the side of the road and Lorenz lying flat on his belly with his field glasses studying some ducks. She said, "You've forgotten your class." He said, "Oh yes I did! But this was so interesting, I just couldn't miss it." Mayr also remarked that Lorenz did not fully understand natural selection, because he repeatedly said that this or that was good for the species. However, the target of natural selection is not the species but only the individual.
Like most of us, Mayr was intrigued by the homing ability of birds, that is, their ability to return to a known goal over an at least partially unknown flight-route. He reviewed the results of experiments conducted by German ornithologists who transported swallows and starlings from their breeding sites up to several hundred miles away in different directions and released them. A high percentage of these birds returned home in a relatively short time (Mayr 1937d, 1944l; see also Mayr 1952j, 1953j).
The origin of the migration routes of several species which fly across vast ocean expanses to winter on small isolated islands of the central Pacific (e.g., the Bristle-thighed Curlew Numenius tahitiensis from western Alaska and the Long-tailed Cuckoo Eudynamis taitensis from New Zealand) is consistent with the geological assumption that large archipelagos were extant in the Pacific during the Tertiary as they are at the present time (Mayr 1954l). This conclusion has been substantiated later by studies in conjunction with the theory of plate tectonics. Without this assumption it would be "difficult to believe that such a migration as that of the Bristle-thighed Curlew could have evolved in the face of the tremendous dangers that the establishment of such a route of migration must have faced" (p. 392).
The surprising preponderance of males (70-80%) versus females in several species of the honeyeater genus Myzomela which Mayr had noticed in New Guinea and later in the museum collections directed his attention to the problem of varying sex ratios in birds (1939a). This paper brought together a large amount of widely scattered information most of which, however, has never been followed up. In two brief notes (1938e, 1938m) he tried to stimulate ornithologists to collect additional field data. A differential vulnerability of the sexes to certain dangers cause a deviation from the ideal 50:50 ratio in adults. A high mortality of females during the breeding season occurs probably in all those species in which the female carries the whole burden of incubation, particularly in ground nestingbirds. Females outnumber males in polygynous species like the weaver birds (Ploceidae). Unequal sex ratios favoring the male or the female sex have been found to be correlated with peculiarities in the life histories of these birds; however, caution must be observed in the use of sex ratio data gathered by field observers.
In one of the few papers coauthored by Ernst and Gretel Mayr (1954g) they demonstrated that the smaller species of owls (wing less than 210 mm) usually molt their tail feathers simultaneous. The small species may require the tail less in flight than the larger ones. In these species (wing more than 230 mm) the tail molt proceeds usually from the outer rectrices inward.
The Sanford Hall of "The Biology of Birds," opened on May 25, 1948, was the first one at the AMNH dedicated to the biology of any group of animals. Mayr was chairman of the planning committee. The hall demonstrated the diversity of species including examples of extinct birds, the constructions of nests; it explained the principles underlying flight, peculiarities of feathers and body (airsacs) as well as migration and evolution (Mayr 1948b). The basic rule was that not a single exhibit should be placed in the hall that did not illustrate some biological principle or generalization. These concepts for the layout were derived from those developed by Bernhard Rensch in Berlin (p. 44). After the opening ceremonies of the Sanford Hall Mayr had serious physical problems like irregular heart beat, from which he suffered for more than 5 years. The cause may or may not have been the pressure to finish the job in time and to stay within tight budget limits see (p. 302).
Once again Mayr planned to write a comprehensive book, Natural History of Birds for which he signed a contract in July 1940.9 The manuscript was to be submitted in 1942. However, this project was laid out too exhaustive and never completed because of other more pressing tasks. He confessed to his colleague Wilhelm Meise in Berlin on 4 January 1950, almost 10 years after signing the contract:
"Concerning my own book on the biology of birds, the trouble is that I always seem to have so many other jobs to perform. This spring I shall give courses at Columbia University and will have little time for my own research and writing. However, for your information, I will send you an outline of the book as far as I have planned it, also part of the more detailed outline concerning the egg, the care of the eggs, and the care of the young. None of this is, of course, final. It always
9 At that time, L. C. Dunn (Columbia University, New York) finalized the program of the Jesup Lectures on "Systematics and the Origin of Species" (see p. 190-193) and Mayr wrote to him on June 21, 1940 in a vain attempt to postpone these lectures: "I have had an offer from Oxford University Press to prepare a textbook on ornithology. This means so much to me and to my future that I can ill afford to turn it down in favor of the systematics' project. Maybe I can accept your kind invitation to lecture at Columbia by changing the subject. I could possibly use the notes assembled for the preparation of my textbook on ornithology, to give a really serious course of ornithology. I might be ready for this in the winter of 1941 to 1942." However, preparations for the systematics lectures to be held in March 1941 were too far advanced for any changes to be considered.
happens that when one works on a book like this, one has to rearrange the material. I want to accomplish primarily two things: (1) a clear presentation of the more interesting facts concerning birds, and (2) a reference to the most recent literature throughout the world. Too many of the books on bird biology seem to be merely copies, slightly paraphrased, of some earlier book on the subject. The difficulty that I have found up to now is that it seems to be impossible to stay within the stated limits. There is such an infinite variety of information available on birds that one really doesn't know where to stop. Parts of my manuscript are already typed and I may send you some of the typescript for your information. I would prefer if we do not go beyond this at the present time because I really don't quite know yet what I can do during the next year or two. The contract which I have with the publisher, Oxford University Press, is very elastic and it would cause no difficulties to include a co-author. I am very much interested in the possibility of doing this together with you. I think the publisher would like to have the volume well illustrated but perhaps a little more in the American rather than in the German way. This means that they are anxious to have illustrations of high artistic value and popular appeal rather than of great scientific value."
Subsequently, Mayr turned all of his material for such a book over to W. Meise (then in Hamburg) who used some of it for his three-volume Natural History of Birds (1958-1966) published in coauthorship with Rudolf Berndt.
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