(62) THE GREAT CRESTED GREBE ENQUIRY, 1931, (PART I.) BY T. H. HARRISSON AND P. A. D. HOLLOM, CONTENTS. 1. INTRODUCTORY. 2. THE CENSUS, 1931. England and Wales, Scotland. Holland. Belgium. France. Italy. Denmark. Norway. Sweden. Finland. Asia. 3. HISTORY, (a) Geological Data ; the Great Crested Grebe is Prehistoric. (b) Past Centuries. (c) The Early 19th Century. (d) Ancient Sites. (e) The Massacre. (/) The Bird Protection Acts, 1870-80. (g) After the Act of 1880. (h) Phases of Increase. (i) Comparison of Counties. 4. PRESENT NUMBERS. fa) Present Distribution ; the System of Spread. lb) Comparison of 1930 and 1931. (c) Deserted Sites in connection with the above. (d) The Widespread Nature of Increase. (e) Factors Controlling Present Distribution and Increase. (/) Relative importance of these Factors. 5. OTHER POPULATION PROBLEMS. (a) Non-breeders. (b) Distribution at Sea. (c) Migrations. 6. FOOD-HABITS. (a) Special Results of Aquatic Life. (&) Weights. (c) Food-habits. (d) Dives. (e) Dive-speeds. (/) Preening. (g) Feather-eating. (h) Flight. 7. RELATIONS. (a) Mortality, (b) Territory. (c) Relations with other Species. (d) Parasites. 8. NEST-HABITS. (a) Share of Sexes. (b) Courtship. (c) Nest-sites. (d) Nesting Dates. (e) Incubation. (/) Number of Eggs. (g) Number of Young. (h) Double Brooding. (i) Remarkable Behaviour on Land. 9. SUMMAR(j) BehaviouY ANDr CONCLUSIONSat Sea. 64 BRITISH BIRDS. [VOL. XXVI. I. INTRODUCTORY.* THE Great Crested Grebe Enquiry, 1931, arose from an ecological study of aquatic birds in Surrey during 1930. The results of this work led us to follow up certain special lines of enquiry, especially the distribution and habits of the Great Crested Grebe (Podiceps c. cristatus). We chose this bird because it had increased to an extraordinary extent in the past fifty years, and the factors, stages, and innumerable repercussions involved in the increase of one species seemed to us a little known matter of great importance. The numbers in 1931 were to act as a standard for comparison with past and future status, having no intrinsic value in themselves. The bird was also conspicuous and unmistakable, with «. limited habitat (fair sized lakes) which would greatly simplify a detailed study. For these reasons the Great Crested Grebe seemed ideal for our purpose. The enquiry has been the work of the authors in co-operation throughout, and has been greatly facilitated by the invaluable advice and support of H. F. Witherby. With both of us the enquiry has been a hobby, and has had to be subordinated to our regular jobs. We can recommend this sort of hobby for those people who find life dull; it has involved us in some five thousand letters from fifteen countries. Scope of the Enquiry.—Our object in instituting this enquiry was to obtain a census of breeding Great Crested Grebes in England and Wales. We also hoped to cover Scotland as adequately as possible. In addition to ascertaining the numbers of pairs on all lakes in 1931 we desired to discover the approximate date on which each lake was first colonized, the numbers of pairs in other years, and the history of any lakes once inhabited but now deserted by Grebes. A schedule for this information was issued and circulated through British Birds ; the text of this schedule was printed antea XXIV., p. 253. A number of supplementary questions on eggs, nests, territory, non-breeding birds, mortality, migra­ tions, food, etc., were added, as we considered these important in considering the success and the future of the species. *ln the organization of this enquiry most of the correspondence with naturalists was done by T.H.H., landowners and keepers by P.A.D.H. All lists of lakes, filing and sorting of data was done by P.A.D.H. The writing up of results and publications in connexion with the enquiry became mainly the affair of T.H.H., who is responsible for the text of this Report ; sections have been drafted by P.A.D.H., J. C. S. Ellis, C. H. Hartley and E. C. Rowberry, but these have always been revised and rewritten by T.H.H. This arrangement seemed necessary to ensure coherence and an even treatment throughout. Miss L. M. Bates typed the whole Report. VOL. xxvi.] GREAT CRESTED GREBE ENQUIRY. 65 In order to assure the maximum of response, appeals for help were published in daily, evening and local newspapers, weekly and sporting papers, angling and scientific journals, and a special feature in The Times. The B.B.C. kindly broad­ cast an appeal at the beginning of the general news, while British Birds, The Scottish Naturalist and The Naturalist published special articles on our behalf. We wrote personally to every well-known naturalist and ornithologist, to many local observers, taxidermists, town clerks and clergy with lakes in their parishes ; we circulated a great number of land­ owners with likely lakes on their property ; and we did every other conceivable thing to make the enquiry a truly national one. Success of the Enquiry.—As a result of all this publicity an enormous response was received, and something very near the maximum of returns was obtained. About one thousand lakes were visited and reported on during the summer by over one thousand three hundred observers. Landowners in every part of the country gave invaluable assistance, often detailed and more accurate than that supplied by ornithologists. Keepers and agents were also very helpful, and not one case of erroneous identification was discovered. A mass of supplementary data was obtained, much of it valuable. Our hopes, then, were fully justified. It has been possible not only to make a satisfactory census of the species in every county, but also to investigate the whole cycle of past history, increase phases and factors, recent decrease and increase, factors controlling distribution, future prospects, and so on. It has been possible to give figures for such widely separ­ ated points as the non-breeding population, young ratios, mortality rate, longevity and total annual food consumption. We have been able to compute and specify the relative im­ portance of such matters as the various factors (covert, food, depth, etc.) in distribution, various species in competition, territorial instincts and colonial nesting. Throughout we have stressed the psychological developmental factors, whose influence is seldom appreciated by ornithologists and yet is vital to an understanding not only of the habits but also the distribution and success of the species. The significance of some of these influences is far wider than in its reference to one species. Always our remarks are based upon definite data obtained in the course of the enquiry. Several points remain undecided; these we have indicated in the text, in the hope that some person, favoured with more time than is at our 66 BRITISH BIRDS. [VOL. XXVI. disposal, will take them up where we have had to leave off. Limitations of the Enquiry.—No investigation is without its errors, and this one is no exception. We trust that the necessary additions will be sent to us, also the corrections. We shall publish these, together with information regarding changes since 1931, and any modifications in our statements that these may entail, some time in 1933. We have been somewhat handicapped in being able to give only our spare time to the enquiry and also by financial considerations. Indeed, we should have been unable to carry on at all had it not been for the support of Mr. Witherby and British Birds. As it is, the expenses we had to provide were so considerable that we were prevented from operating several schemes which we hoped to undertake in connexion with the enquiry. The only other serious limitation was one of our own making. We decided, as a matter of policy, that we would handle no dead Grebes during the course of the enquiry, for the bird is protected, and the success of this sort of work is partly dependent on the good-will of strong protectionists. Acknowledgments.—It would be impossible to acknowledge here our indebtedness to the 1,300 persons whose names have reached us as helpers in this enquiry, as well as the unknown numbers whose data have been absorbed and summarized in the reports of other observers and county organizers. We have wherever possible acknowledged their help direct and would only repeat that we are deeply grateful for their help in making this enquiry a success. All those who have sent in data in any way relevant are named in the list of helpers for every county. It is, however, necessary that we should mention certain people who have devoted a great deal of their time to this enquiry. We should like especially to acknowledge the help of J. C. S. Ellis, C. H. Hartley and E. C. Rowberry in writing up reports ; Miss Calloway, Miss Janet Clark, W. R. D. Harrisson, Miss E. P. Leach and Miss Plummer in arranging data ; L. A. Hawkins and W. H. Perrett in pursuing references; Miss L. M. Bates and Miss Lawson in clerical work. N. B. Kinnear and Dr. Percy Lowe have given us every facilitv for working up our data in the Natural History Museum, and Mr. Kinnear has given us much help in other directions. Invaluable as " flying squads ", to fill any gap or save any crisis, have been W. B. Alexander, E. M. and B. D. Nicholson ; of much help with criticism and advice C. S. Elton, Rev. F. C. R. Jourdain, D. L. Lack, Dr. T. G. Longstaff and E. M. Nicholson. VOL. xxvi.] GREAT CRESTED GREBE ENQUIRY. 67 Without the decentralization of counties or large areas our work would have been far more complicated, and in this connexion we are very grateful to H.