NOTES AND COMMENTS

LOONS AND THEIR WINGS

ROBERT W. STORER University of Michigan Museum of Zoology, Ann Arbor

In his interesting article on adaptive evolu­ Like the Hesperornithes and the grebes, the tion in birds' wings, Savile (1957) makes sev­ loons are foot-propelled diving birds. While eral statements about the loons and their evolu­ they may swim by alternate strokes of the feet tion which I feel require further discussion. when on the surface, they move the feet simul­ The idea that loons were relatives of the taneously when they are below the surface. Upper Cretaceous Hesperornithes and are there­ Ordinarily the wings are kept folded and under fore primitive has persisted in the literature for the flank feathers while the birds are under . many years, although in my opinion it is quite water; however, in turning sharply or when unjustified. As I have recently pointed out wounded or pressed, loons use their wings under (1956) the best known of the early fossil loons water (Townsend, 1924). The speed with which (Colymboides minutus) was a small species loons normally move under water is indicative which, compared with modern loons, had legs of the size and power of their hind limb mus­ only moderately adapted for propulsion under culature, which, compared with other birds, water and relatively large wings, enabling it to forms a relatively high proportion of the total fly strongly. Loons as we know them evolved body weight. Yet loons can and do perform between the time of Colymboides minutus (late long migrations. Thus loons appear to be Oligocene or early Miocene) and the Upper adapted for sustained flight with a minimum Middle Miocene (Calvert formation), the age weight of wings and pectoral muscles. An im­ of occurrence of the earliest recorded fossil of portant evolutionary factor is the conservatism the Recent genus Cavia (Wetmore, 1941). of wing proportions within the loons (and many Loons probably evolved from gull-like ances­ other groups of birds). I have shown the re­ tors; certainly they evolved from strong-flying markable similarity in the proportional lengths ones. of the wing elements between Colymboides As has been pointed out by Stolpe (1935) minutus and the Recent loons (1956: 415), and and others, the similarities shared by the Hes­ it is evident through what is known of their perornithes, the grebes, and the loons result evolution that loons' wings have changed little from convergent evolution. I see no valid rea­ if any in their proportions. There has, how­ son for believing that they had a common ever, been a reduction in relative size of the swimming ancestor. The Hesperornithes were fore limb as the hind limb has become increas­ highly specialized end products of a very early ingly heavy. What we have in modern loons adaptive radiation of birds. There is no con­ is an adaptive balance; the selective advantages clusive proof that any other known Cretaceous of an increasingly strong (and heavy) hind birds possessed teeth. The retention of these limb being opposed by the disadvantage of the structures in the Hesperornithes was of un­ accompanying increase in wing-loading. doubted selective advantage-witness the evolu­ Speed in flight is a compensation for a high tion of analagous structures in the bills of wing-loading, and I suggest that the form of mergansers. Neither the adaptive "disadvan­ loons' wings is an adaptation for speed in flight tage" of weight nor the "substitution" of a :'necessitated" by an increase in wing-loading, muscular gizzard discussed by Dilger (1957) as In turn brought about by the strong develop­ reasons for the loss of teeth in birds applied to ment of the legs for propulsion under water. these flightless birds which presumably used In using data on weights and wing areas it their teeth to hold their prey. should be emphasized that the weights of mi­ gratory birds, and hence the corresponding Thus loons were derived from birds which figures for wing-loading, are extremely variable. flew well, and they were not related to the I have been collecting data on the grebes and Hesperornithes, which died out long before have found more than 100 per cent variation in loons became their ecological counterparts. The wing-loading in the Pied-billed Grebe. Two wings of loons must therefore be thought of as males of this species, each having a wing area either in the process of "degeneration," or as of 52 square inches, weighed 282 grams and being adapted to a particular set of conditions. 576 grams. The figures for wing loading are I would like to present evidence for the latter 1.75 and 3.55 pounds per square foot respec- view. tively. ' 262 NOTES AND COMMENTS 263

LITERATURE CITED STORER, ROBERT W. 1956. The fossil loon, DILGER, WILLIAM C. 1957. The loss of teeth Colymboides minutus. Condor, 58: 413-426. in birds. Auk, 74: 103-104. TOWNSEND, CHARLES W. 1924. Diving of SAVILE, D. B. O. 1957. Adaptive evolution in grebes and loons. Auk, 41 : 29-41. avian wing. EVOLUTION, 11: 212-224. STOLPE, M. 1935. Colymbus, Hesperornis, WETMORE, ALEXANDER. 1941. An unknown Podiceps: ein Vergleich ihrer hinteren Ex­ loon from the Miocene beds of Maryland. trernitat, Jour. fur Ornith., 83: 115-128. Auk, S8: 567.

THE LOON WING

D. B. O. SAVILE Botany and Plant Pathology Laboratory, Science Service, Ottawa, Ontario

I regret that, in following Heilmann (The from a line that, although capable of flight, origin of birds. Witherby, London. 1926), I failed to develop a really efficient wing. In par­ unwittingly perpetuated an error concerning the ticular, I find it difficult to believe that the relationship of H esperornis. I wish to thank poorly developed loon alula is anything but Dr. Storer for drawing attention to this error, primitively inefficient; for, as long as a bird of and I trust that his correction will be widely substantial size flies at all, a functional alula is noted. very valuable, and it is hard to believe that it is Dr. Storer's interpretation invalidates the detrimental in swimming or diving. chronology of my speculative interpretation of I am grateful to the many correspondents who the origin of the loon wing. Whether it upsets have written to me about this problem, but it it in other respects is a moot point. I still feel must be admitted that none has yet presented a that it is quite possible that the loons arose convincing alternative solution.

CROSSING RELATIONSHIPS IN THE GENUS CARICA

ANAND C. SAWANT

The cultivated papaya (Carica papaya) is na­ work was undertaken, therefore, to study the tive to Central America (1) and in the post­ crossing compatibility relations of wild species Columbus period it spread to other tropical of Carica with cultivated papaya, a prerequisite parts of the world. Papaya cultivation is sub­ to the transfer of any desirable characters from ject to serious depredations primarily from wild species to cultivated papaya. many fungus, bacteria and virus diseases. In Many successful, as well as unsuccessful, inter­ subtropical countries, on the fringes of tropics, specific crosses have been reported. Warmke the papaya cannot be grown because it is very and others (2) reported a new interspecific susceptible to temperatures below 400 F. Ef­ cross, C. goudotiana X C. monoica, the latter forts are being made therefore to develop va­ being used as a male parent. Addison (3) had rieties resistant to diseases prevalent in the succeeded in making the interspecific cross, C. particular area, and to develop varieties for papaya X C. monoica. Still earlier successful subtropical climates. crosses were made between C. candamarcensis The papaya belongs to the genus Carica, X C. papaya, C. caulifioro X C. papaya, C. which has some 40 species native to Central erythrocarpa X C. candamarcensis, C. papaya X America and Northern part of South America. C. gracilis (4). Seany and Wieland have been C. monoica shows some tolerance to one of the successful to cross C. candamarcensis X C. virulent papaya diseases called virus Bunchy monoica and to study F, and F. (personal cor­ Top, which is common in Puerto Rico and the respondence) . In the present work crosses be­ adjoining Carribean area. C. candamarcensis, tween four species, namely C. papaya, C. on the other hand, grows only at an altitude of monoica, C. goudotiana and C. caulifiora were 4,000 feet or more, which has much cooler attempted. climate for papayas. The fruit of C. cando­ C. papaya is a tree growing 10 to 25 feet or marcensis is edible. The present exploratory more. Usually unbranched, it bears large melon-