Sea Terns
Sea Terns or Sea Swallows. By George and Anne Marples.
' (Country Life. 15s.)
LET it be said at the outset that this is an excellent and praiseworthy book, packed with meat for the professional ornithologist, and full of interest for the amateur bird-lover. It is based on first-hand observation and study throughout -indeed it might be called a fault that the authors have not gone at greater length into the observations of others.
Every aspect of the life of the British species of Sea Terns is taken into account. The first two chapters deal with the differences between Sea Terns and Marsh Terns, and the diagnostic characters of the British species. Here are included some very useful scale figures of the various forms. Then follow sections on the known terneries of Britain, and on the seasonal movements of the birds, with valuable diagrams of the latitudinal ranges of the different species, and of the recoveries of ringed birds. A long chapter on courtship and the relations of the sexes is crammed full of fascinating material. A criticism 'lee is that its value .would have been considerably enhanced if pen-and-ink sketches had been given of the various attitudes and cere- monies described, since these are difficult to visualize from printed descriptions alone, and for some reason the authors' photographic documentation is here very scanty.
The next chapter " Of Tracks " contains some interesting observations on the traces left by the birds in the sand, which in the hands of the authors have been made to yield additional information on the courtship and other habits of the terns. Then follow accounts of nests, eggs and young ; of the food of terns and their methods-of obtaining it ; and of the enemies of terns. A chapter, " Of Alarms, Dreads, and Panics," is devoted to the curious habit of term of flying off in small or large groups under the influence of fear, for which no cause can be discovered. Then we have a chapter on the various interesting experiments conducted by Mr. and Mrs. Marples to find out how terns recognize their own nest and eggs, whether they would recognize as their own eggs removed some distance from the nest, and so forth. A descriptive chapter on the calls and notes of terns is followed by a very interesting discussion of their fluctuations in numbers, their desertion of old terneries and their founda- tion of new ones. And finally we have a charmingly written chapter, designed to give pictures of the atmosphere of a • big 'ternery at different times of dairr iidunder different conditions -of season and weathei. There goodindek; With such a wealth of material, it is difficult to select points for mention or discussion in a review. Some very interesting facts are brought out in the discussion of the fluctuation,s in the terns' numbers at certain terneries in various years. It appears established that off the Norfolk coast, for instance, the swarms of 'small. -fish -on which the birds -My• to feed themselves and their young -are exceedingly abundant,- while in other years, for unexplained reasons, they fail to show up. In these years of dearth, there is a fearful mortality of the young birds. Further, the Sandwich Terns, at least, will desert a breeding site on account of food shortage.
Our authors have also some very pertinent things to say on the reasons for the increasing or decreasing abundance of terns. They make it perfeCtly clear that neither the taking of eggs, even on a large scale, nor the shooting of adults, need cause any -diminution in numbers. By far the most important reason for diminution is the rendering of existing breeding grounds unavailable to the birds. This is chiefly the result of direct human interference, as when a breeding site is engulfed by the spread of a city, or iikincluded in a golf-course, or becothes too much frequented by summer visitors. It may also be indirectly the result of human inter- ference, in the form of indiscriminate " protection." For instance, the terns on a well-established ternery in Anglesey have now been crowded out by over-protected gulls and cormorants, and similar happenings are reported elsewhere. It is becoming increasingly clear that the sentimentalist form of protection which aims at prOtecting any and every species of bird indiscriminately will in many cases defeat its own ends and lead to the disappearance of rarer - birds, ousted by tougher and commoner species. Science and the scientific method are needed in bird protection- as in other spheres.
The experiments on eggs and nests brought out a number of interesting points—that some colours, notably red, painted on the eggs, alarmed the birds and prevented them brooding their own eggs ; that the birds recognized their own nest even when the site was thoroughly altered by putting stones round the nest and planting grass and large plants near it ; and that the chief reason why many terns do not line their nests with plant material and are content with a mere sand-scrape is not inherent lack of the nest-building impulse, but merely lack of material in the immediate vicinity.
In writing a book of this sort, an author is faced with a dilemma. Either he must make it a straightforward account of the species he has selected, neglecting the comparative method and the discussion of the general principles involved ; or he is faced with a most difficult task of selection, and runs the risk of swelling his book to unmanageable size. Our authors have chosen the first method, and they have made a success of it. Here and there, however, the defects of. the method are apparent. For instance, the record of their experiments would have been more interesting if they had attempted some comparison with similar experiment§ on other birds, notably on related species ; and their account of " courtship " and display definitely suffers from not being discussed against' a background of general principles.
• As regards detailed criticisms, I hope that congerie .is a misprint for congeries, but fear it is an attempt—perhaps on analogy with lingerie—at a singular ! On p. 167 " on the ground " is used twice in one sentence, once literally and
once metaphorically. . -
In the account of the relations between the seies, the tiresome human terms " lady," " swain," &c., are frequently used with irritating effect. On p. 157 the assumption that it is surprising for conspicuous birds like terns to have few enemies 'seems an example of inverted biological reasoning : presumably enemies are not major factors in restricting the abundance of terns, and therefore terns can be conspieuous. On p. 120, the estimates of terns' length of life seem based on most inadequate evidence, and are quite likely to be subject to an error of 50 or 100 per cent. : in spite Orthis, they are later used in arithmetical calculations worked out to two places of decimals !
These, however, are minor points. The book as a whole is, let me repeat, an admirable one. We need monographs of this type, thoroughly workmanlike by every biological
• Standiird-, and fascinating to the bird-lover -and general reader, on "every' kind of :bird. They are valuable-=in themselves, and valuable also as constituting the material iiiitnOtwhich a truly scientific field ornithology will one day be assembled.
JULIAN HUXLEY.
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