(138) PUBLICATION OF THE BRITISH TRUST FOR ORNITHOLOGY. REPORT ON GREAT CRESTED GREBE SAMPLE COUNT, 1935. BY P. A. D. HOLLOM. DURING the summer of 1935 a sample count of Great Crested Grebes (Podiceps c. cristatus) was taken in , Scotland and Wales. The main object of this count was to discover the effect of the severe drought in some parts of the country during 1933 and 1934, and also to trace the general trend in numbers and distribution since the complete census of 1931 (see British Birds, Vol. XXVI., pp. 62/92, 102/131, 142/195). The areas chosen were well spread geographically and included waters in Wales and Scotland ; various other waters were also reported on, but the request in British Birds for casual observations met with very poor response. Most of the counts were made in June, and the numbers of non-breeders in particular refer to that month. THE 1935 SAMPLE COUNT. The following table gives the counts made in the selected areas together with the numbers for the same waters in 1931. For full particulars reference should be made to the detailed lists of occupied waters given at the end of the report. T935- i93i- Breeding Non-B. Total Breeding Non-B. Total. Pairs. Birds. A dults. Pairs. Birds. A dults. *Berks. ... 34/36 13/17 85 35/37 5 75/79 •Bucks. 17/18 15/17 51 11 2 24 •Cheshire 74/80 38/42 190/198 78 38 194 I I •Essex 7/ 8 30 64/66 33 31 97 •Leicester. 34 8 76 32 — 64 •Middlesex 10 27 47 15 5 35 •Oxford 14 1 29 15/16 — 30/32 •Somerset 17 15 49 17 5 39 Herts, (part) 23/28 18 64/74 31 35 97 Norfolk (some broads) no — 220 107 — 214 (part) 27 9 63 32 — 64 Yorks. (part) 48 8 104 47 — 94 South Wales (part) 16 — 32 15 — 3° Forth & Tay areas (part) 45 9 99 35/38 — 70/76 Other waters 33/35 52/55 121/122 57 19 133 Total 0.519/536243/2561,294/1,315! c.560/566 140 1,260/1,272 *A complete census was taken in these counties. VOL. xxx] REPORT ON GREAT CRESTED GREBE. 139

1935 1931 Breeding Non-B. Total Breeding Non-B. Total Pairs. Birds. A dults Pairs. Birds. Adults. Say 528 249 1.305 563 14° 1,266 Increase or Decrease on 1931 —35 + 109 + 39 Percentages on 1931 figures 94% 178% i°3% In 1931 about 1,240 pairs were found in England, Scotland and Wales, so that the 1935 count represents a sample of 45 per cent. The 1935 figures show a decrease of about 35 breeding pairs or 6 per cent. ; an increase of 109 non-breeding birds or 78 per cent.; and an overall increase in population of 39 birds or 3 per cent. In 1931 the question of non-breeding birds was one of several supplementary points on the reverse side of the enquiry schedule, whereas in 1935 there were adjacent columns in which to enter breeding and non-breeding birds. Moreover it was known that one of the objects of the present count was to find to what extent the breeding population had been upset by the drought. There was, therefore, a tendency to require more positive evidence in 1935 than in 1931 before a pair was entered as breeding, especially as no indication had been given to observers as to what should be counted as breeding birds and what as non-breeding birds. One observer who found two Grebes, evidently paired, on a water and did not see nest or young, but was unable to search the available cover, reported them as a breeding pair. Another observer, on similar evidence, reported non-breeding birds. But the majority did not give their reasons for including birds as breeding or otherwise, and so no attempt has been made to sort the records on a uniform basis ; they have been accepted as they stand. Consequently the increase in the proportion of non-breeders to breeders has been exaggerated and the 1935 figures for breeding pairs are not strictly comparable with those for 1931, when, generally speaking, pairs present on territories were included as breeding.* Therefore in the tables comparing the 1931 figures with those for 1935 both breeding and non- breeding birds have been included, and the total number of adult Grebes on each water is shown. •As an example, reference may be made to the last table on p. 80 of the 1931 report (Brit. Birds, Vol. XXVI.) which shows that on ten waters twenty-one of the forty " breeding " pairs did not nest. 140 BRITISH BIRDS. [VOL. XXX.

THE DROUGHT. An exceptionally long period of dry weather began in November, 1932, and lasted for two years. Over England and Wales the rainfall for 1933 was 6.6 inches less than the

Rainfall, Seasonal year, as per cent, of average. average and in 1934 there was a further deficiency of 1.7' inches, in spite of an excess of about 3 inches in December which in many places was the wettest December on record. The year 1935 continued to make good the shortage, and the excess for the year was about 5 inches. In Scotland, although VOL. xxx] REPORT ON GREAT CRESTED GREBE. 141 1933 was an unusually dry year, the average rainfall was exceeded in both 1934 and 1935. On page 140 will be found a map reproduced by kind permission of the Controller of H.M. Stationery Office from British Rainfall, 1934, showing the rainfall for the year October 1933 to September, 1934. During these twelve months the deficiency of rain steadily accumulated, and almost reached its peak, and it is therefore perhaps the most significant period of the drought so fat- as Grebes are concerned.

ACCUMULATED DEFICIENCY OF RAINFALL. (Taken from British Rainfall, 1934). Period. England Scotland. and Wales. inches. inches. November 1932 to March, 1933 1.7 0.2 July, 1933 3-5 0.9 September, 1933 • 5-8 4-3 December, 1933 9-7 9-7 ,, March, 1934 . 11.4 11.2 July, 1934 13.1 7.8 ,, September, 1934 . 13-1 5-8 November, 1934 14.9 5-7 ,, December, 1934 . 11.5 4.6 The average annual rainfall in England and Wales is 35.2 inches, and in Scotland 50.3 inches. Although sufficient information is not forthcoming to obtain an exact idea of the extent to which the Great Crested Grebes were affected at the height of the drought, it is clear that there were considerable disturbances and readjustments, particularly in 1934. This is well illustrated by the following examples of some of the more startling changes in that year compared with 1931. At Tatton Mere, Cheshire, there were 7 pairs in 1931 and 2 pairs in 1934 ; at Tring, Hertfordshire, 25 pairs in 1931, and none in 1934 ; at Blagdon, Somerset, 12 pairs in 1931 and 3 pairs in 1934 ; at Hornsea, Yorkshire, 10 pairs in 1931 and about 19 pairs in 1934 ; at Llangorse, Brecon, 13 pairs in 1931 and 20 pairs in 1934. Only a small proportion of the waters was still affected by the drought in 1935, and the waters concerned were spread throughout the country, very few areas escaping altogether. The Grebes suffered on only half the waters that were affected in this way, while in three localities (in Essex, and Middlesex) the lower level resulted in a better growth of nesting cover. The reports on the state of the waters in 1935 are tabulated below. 142 BRITISH BIRDS. [VOL. XXX.

DROUGHT EFFECTS. Material No. of Reduction A Averse Waters. in water Effect on level .1935- Grebes, 1935 Berks. 22 — .—. Bucks. II 1 — Cheshire 36 6 4 Essex 10 1 1 Leics. 12 3 •—. Middlesex ... 9 3 2 Norfolk 15 —. Oxford 8 1 — Somerset ... 8 — .—. Surrey 18 4 2 Yorks. 15 4 2 Wales ... . •. 2 Scotland 26 3 2 Other waters 28 9 5 220 35 18

DECREASE OF BREEDING PAIRS. In considering the decrease of breeding pairs it is noteworthy that it is more than covered by the decreases in pairs at reservoirs ; in fact, the decreases in almost every area are due to losses at waters of this type. The net reduction of about 60 pairs at reservoirs is made up as follows:—• Increase. Decrease. Bucks. Weston Turville .. — Cheshire Baddiley .. — 3 Bosley .. 0/1 -— Hurleston 1 — Sutton .. — — Walton 1 — Essex Lea Valley .. — 17 Herts. Cheshunt .. — Elstree ... .. — 3 Tring .. — 5/1° Leics. Blackbrook .. — 2 Cropston .. — 1 Knipton ... .. — •— Moira — 1 Saddington .. — —• 4 — Thornton 2 — Middlesex Ruislip ... .. 4 Stoke Newington .. 2 Northants. Stanford .. . 12 Westhorpe ,. 6 Oxford Clattercote .. — Carried forward: 8/9 56/61 VOL xxx] REPORT ON GREAT CRESTED GREBE. 143

Increase Decrease Brought forward: 8/9 56/61 Somerset Blagdon ...... — 2 Chard ... 1 •— Litton ...... — Staffs. Bellfields — 6 Dimmingsdale ...... — 1 Warwicks. Wormleighton ...... — I Worcs. Bittell — 3 Yorks. Chelker ...... — — Gouthwaite ...... 1 — Ryhill ..' 2 — Fife Kinghom 1 •— Peebles, Portmore ...... 1 — Midlothian Bavelaw ...... •— 1 Cobbinshaw ...... •— 2 Gladhouse ...... — —

14/15 72/77 Less increases 14/15 58/62 18 Reservoirs showed decreases totalling 72/77 pairs. 9/10 ,, ,, increases ,, 14/15 ,. 9/10 ,, „ no change — 37 Reservoirs. Net Decrease 58/62 pairs.

It follows that the natural waters show a net increase of about 25 pairs, and it would appear that many local decreases and increases are merely the redistribution of birds between natural waters and reservoirs where the effect of the drought was accentuated. But much more significant than the failure of the reservoirs to maintain their population of breeding Grebes, is the fact that if the areas counted in 1935 are grouped according to their increase or decrease of nesting pairs, they fall into two main geographical divisions. All the decreases, except the possible one in Cheshire, are confined to counties in the Thames Valley, or those adjacent to them on the north, and in all other areas there is either no change or an increase in the number of breeding pairs. Buckinghamshire is the only county in the Thames Valley group to show an increase. This increase, however, is fully covered by the decrease of 50 birds at the Tring reservoirs (Hertfordshire) which are bordered on two sides by Buckinghamshire, and if Buckinghamshire is con­ sidered in conjunction with the neighbouring counties of Northampton, Oxford, Berkshire, Middlesex and Hertfordshire, there is a net decrease of about 26 pairs for the six counties. 144 BRITISH BIRDS. [VOL. XXX.

AREAS SHOWING INCREASE OF BREEDING PAIRS. Breea Hng Non-Breeding Pairs Birds. 1931 1935 1931 1935 Scotland (Tay and Forth areas) Increase 37 45 0 9 Yorks. .. 47 48 0 8 Leics. .. 32 34 0 8 Norfolk ,, 107 no 0 0 South Wales .. 15 16 0 0 Gloucs. 0 2 0 0 Bucks. 11 17/18 2 15/17 AREAS SHOWING NO CHANGE OR DECREASE OF BREEDING PAIRS. Breeding Non-Breeding Pairs. Birds. 1931 1935 1931 1935 Essex Decrease 33 17/18 31 30 Herts. .. 31 23/28 35 0 Middlesex .. 15 10 5 27 Surrey ,. 33 27 0 9 Berks. .. 35/37 34/36 5 13/17 Oxford ,. 15/16 14 0 1 Nortaants, . ,, 33 13 9 35/36 Cheshire (Pro! sable decrease or no change) .. 78 74/8o 38 40 Somerset No change 17 17 5 15 These areas of decrease correspond remarkably closely with those parts of the county which received during the year October 1933 to September 1934 only 70 per cent, or less of their average annual rainfall, as shown on the map on page 140. In the case of counties only partially covered, the area shaded on the map corresponds roughly with the proportion counted rather than with the actual position of the waters visited. Both, however, are combined where possible ; for example, the north-eastern half of Surrey is shaded and in Norfolk two-thirds of the county working from the south-east (Broads district). In Gloucester and South Wales (Brecon and Glamorgan), although only some of the possible sites were visited, more Grebes were found than in the complete census of 1931, so the whole counties have been shaded, as decreases there are impossible. From the sample, then, there appears to be close conformity between the distribution of rainfall and that of the decrease of nesting Grebes. If it is permissible to assume that the sample is fully representative of the whole country, the following calculations may be of interest. On the waters visited in the counties which in 1933/34 received only 70 per cent, or less of the average rainfall (i.e., Kent, Surrey, Sussex, Hants, Wilts., Berks., Oxon, Map showing approximately the areas counted in 1935, and the relative density of Great Crested Grebe population compared with 1931- 146 BRITISH BIRDS. [VOL. XXX. Bucks., Middlesex, Herts., Essex, Cambs., Beds., Hunts., Northants. and Cheshire) numbers have fallen from 285 pairs in 1931 to 237 pairs in 1935, a decrease of 16.8 per cent. Elsewhere the shortage of rainfall was not so severe and numbers have risen from 255 pairs to 272 pairs, an increase of 6.7 per cent. In 1931 the counties specified above held about 480 pairs, and a decrease of 16.8 per cent, would amount to a decrease of 81 pairs. The rest of the country in 1931 held about 760 pairs and an increase of 6.7 per cent, would mean an additional 51 pairs, leaving a net decrease for the whole country of 30 pairs. This compares with the decrease of 35 pairs found by the sample count of just under half the country. Whether or not these assumptions are justified, it does at any rate appear that the sample is unduly weighted towards decrease by the high proportion of Thames Valley counties which have been included. NON-BREEDING BIRDS. As already mentioned, the increase of non-breeding birds is probably not so great as it appears, but after full allowance has been made for the stricter proof of breeding required in 1935, there appears to remain some increase of non-breeders. This is particularly the case in the areas which show an increase in the number of breeding pairs ; in three of these counties there were no non-breeders in either year, while the other four counties each have increases of eight or more non-breeders. In the areas of decrease of breeding pairs non-breeders have been reduced only in Essex (1 bird) and Hertfordshire (35 birds). In nearly every other county they have increased substantially, and the only counties where breeders and non-breeders combined were appreciably lower in 1935 were Essex, Hertfordshire and Northamptonshire. It is not known at what age Grebes begin breeding, and until this is ascertained it is impossible to judge with any certainty the significance of an increase in non-breeders. It might be caused by the inability of birds in breeding condition to find suitable nesting sites, to an unusually good hatch in a previous year, or to conditions unusually favourable for the survival of immature birds after the breeding season. However, for the sake of convenience, all birds hatched prior to 1935 are termed adults. THE INTERMEDIATE YEARS. In an attempt to follow the fluctuations in numbers in the years 1932, 1933 and 1934, the numbers of pairs at the waters counted in each of those years are listed, together with the VOL. xxx.] REPORT ON GREAT CRESTED GREBE. 147 numbers of pairs found on the same waters in 1931 and 1935. The 1931 figure is taken as 100 and the index numbers are therefore as follows :— Index Number, 90 waters in 1932 held 147 pairs (approx.) 89 The same waters in 1935 ,, 153 93 and in 1931 ,, 165 100 69 waters in 1933 , , no 97 The same waters in 1935 , , no 97 and in 1931 , > "3 100 89 waters in 1934 , , 139 77 The same waters in 1935 , - 153 85 and in 1931 . 179 100 But in no case do these groups of waters give the index number of 94 for the year 1935 which as shown on page 139 applies to the sample as a whole. This number of 94, based on about 560 pairs is taken as being more accurate than those obtained by considering the pairs counted in 1932, 1933 or 1934, and it is therefore considered reasonable to adjust the index number for 1935 in each case to 94, and to make a proportionate adjustment to the index numbers for the years 1932, 1933 and 1934. Thus to adjust the index number in the first group of waters (those counted in 1932) it is necessary to divide the numbers for 1932 and 1935 by 93, and multiply by 94 ; this gives the index number of 90 for 1932 and the required number of 94 for 1935. From the second group it appears that the same number of pairs bred in 1933 as in 1935, and the index number of 94 therefore applies to both these years. In the last group the index numbers are adjusted on the same principle as in the first group, giving an adjusted number of 85 for the year 1934. We therefore arrive at the following:— A djusted Index Number 1931 100 1932 90 1933 94 1934 85 1935 94 These figures suggest that the decrease observed in 1931 was continued in 1932 ; that a recovery in numbers took place in 1933, but that in 1934, as a result of the drought, the numbers fell again sharply. It must be stressed that these figures should not be taken as anything more than an indica­ tion of the fluctuations of Grebes, because they are arrived at in such a roundabout fashion, because different waters 148 BRITISH BIRDS. [VOL. XXX. comprised the groups reported on in each of the years 1932 to 1934 and because only 10 to 15 per cent, of the breeding pairs were counted in these three years. THE AREAS COUNTED, (A) COUNTIES COMPLETELY COVERED. Berkshire. Three waters were deserted which had been occupied in 1931. Theale Gravel Pit is the only water which has been colonized since 1931, but several old localities, deserted in that year have been re-occupied and this has done much to offset the decrease of breeding pairs in Windsor Park (Virginia Water and Great Meadow Pond). At these waters the decrease in breeding pairs was accompanied by a corresponding increase in non-breeders, so that there was an increase in the total number of adults for the county as a whole. None of the waters were materially reduced in 1935 by the drought. Buckinghamshire. Two new waters, Rowley Lake and Black Park, have been colonized and two waters have been deserted. Wotton is responsible for the 1935 increase of breeding and non-breeding birds in the county. The fluctuations here are interesting : in 1925 and 1926 four to six pairs bred. There were three pairs in 1930, probably none in 1931 and 1932, but in June, 1935, 20 adults were present, of which five or six pairs were nesting. It seems natural to connect this increase with the great decrease at Tring. The total population of the county has been more than doubled, having increased from 24 to 51 birds. Colnbrook by-pass gravel pit was reduced by the drought but the Grebes did not suffer. Cheshire. Five waters have been newly colonized since the census year and an additional three waters, deserted in 1931, have been reoccupied. The attempt at Hurleston, one of the newly colonized waters, failed because of a drop in the level. Of the five waters occupied in 1931 but not in 1935, lack of water was the cause of desertion of Doddington and Oakmere, but not of Billinge Green, Thornycroft and Witton Flashes. At Tatton only half the birds were able to breed because of the lower water level. The number of Grebes in the county is unchanged at about 194. Essex. This is the only completed county to show a serious decline in the total number of Grebes present in 1935. The population of the thirteen reservoirs, forming the Lea Valley group has been nearly halved and the number of breeding pairs reduced from twenty-four to seven. These reservoirs were at their normal level in 1935, but had been low in 1934. Pollution caused the desertion of Dagenham. AtNavestock Park an extensive plant growth developed on the bed of the lake in 1934. This was submerged in 1935 when the water recovered to its normal level, and in April the banks were found to be lined with putrefying roach and other small fish, killed, it was suggested, by gases given off from the decaying vegetation. Wormingford decoy was reoccupied and Sewardstone Gravel Pit and Eagle Pond have been colonized. Leicester. No new waters have been colonized, but numbers have increased in spite of two desertions. Three other waters showed decreases, and there were increases at four waters, but Mr. H. Kenrick was unable to find much connexion between these changes and the drought. Most of the waters which had been reduced in 1933 and 1934 had recovered to their normal level in 1935. Middlesex. Ashford Gravel Pit is the only newly colonized water. At Ruislip pumping, boating and bathing combined to prevent the Grebes from nesting, and at Stoke Newington one reservoir was dry. VOL. xxx.] REPORT ON GREAT CRESTED GREBE. 149

On the other the usual weed growth failed, so that the only pair which nested was compelled to do so on the grassy bank clear of the water. Nowhere else were drought effects noticed in 1935. By reason of a large increase in non-breeders the number of adults rose from 35 to 47. The non-breeding birds on the large Thames Valley reservoirs, both in Middlesex and Surrey, have not been included because counts for all of them are not available, but it is certain that on these also non- breeders have increased. Oxfordshire. The most interesting record from this county is the breeding of a pair of Grebes in 1934 and 1935 on an island in the Thames near Shiplake. No other new sites were occupied (there are practically none available) and Shelswell Park had only a single bird. Clattercote reservoir was almost dry in 1934 and still several feet below normal in 1935, but two broods were successfully hatched out. There was a very slight reduction in the total number of Grebes in the county. Somerset. Mr. Stanley Lewis was the only observer able to supply details for an entire county for the years 1932 to 1934 ! there were 20 pairs in 1932 and 1933, and 12 pairs in 1934. Blagdon reservoir suffered severely in 1934, an(i very few birds were seen, but there were many at Barrow where there is no cover for breeding. Numbers at natural waters were slightly above average in that year. In 1935 the same number of pairs bred as in 1931, but the non-breeders increased by 10 birds. Chew Magna was deserted because of cleaning operations. (B) COUNTIES PARTIALLY COVERED. In none of the counties under this heading do the waters counted form a complete unit, with no unvisited waters intervening. Devon. In 1931 Slapton was the only water occupied, holding one pair. In 1935 at least one pair was breeding and four adults were seen in July, so there has certainly been no decrease in the county. One pair bred at Blagdon Lake, Ashwater, in 1933 and 1934. Gloucester. The only water which held a pair in 1931 was drained in that year, and the waters which held pairs in 1935 were the only two about which information was received. Hertfordshire. In 1931 ten waters were occupied. Seven of these were visited in 1935 and held 18 to 23 pairs as against 31 pairs in 1931. There were also five pairs on a recently colonized gravel pit. Full details of the effect of the drought at Tring and Elstree have already appeared in BritishBirds (Vol. XXVIII., pp. 250/256, and Vol. XXIX., pp. 28/29), but it should be remembered that these effects must have repercussions elsewhere and this area should be considered in conjunction with the neighbouring counties of Buckinghamshire, Middlesex and Essex. Possibly the fall in numbers at the Lea Valley reservoirs (Essex) in 1935 was due to the refilling and consequent re-occupation of Tring, which was virtually dry in 1934. Norfolk. The count was confined to the broads, which in 1931 held about sixty per cent, of Norfolk's Grebes. Fourteen broads were counted and held no pairs in 1935, (107 pairs in 1931) but there were a number of broads which were not visited. No alterations in water level were reported. Surrey. In 1931 twenty-five waters held 47 pairs. Thirteen of these waters, nearly all in the north and east of the county, were visited in 1935 and held 25 pairs (32 pairs in 1931). In addition two waters, unoccupied in 1931, held one pair each. The level of four lakes was reduced but the birds suffered only at Obelisk Pond and at Godstone. No explanation of the great decrease at Gatton was forthcoming. South Wales. The two waters occupied in 1931 were the only ones reported on in 1935, and show an increase of one pair. It is interesting 150 BRITISH BIRDS. [VOL. XXX. that in 1934 there were 20 pairs at Llangorse, or six pairs more than in any other year for which records are available. Scotland. The count was confined to the Forth and Tay areas where the majority of the 1931 localities were revisited. Drought reduced some of the Midlothian reservoirs and Portmore reservoir, Peebleshire, but its influence could not be traced anywhere in the Tay area. Mr. H. Boase reports that in the area which he works in the Tay valley the numbers have increased from approximately 25 pairs in 1926 to 31 pairs in 1931 and to 41 pairs in 1935. As already noted elsewhere, the drought was much less severe in Scotland than in England and Wales. ACKNOWLEDGMENTS. The names of those who assisted in the count are given below, and I should like particularly to thank those who made themselves responsible for specified areas, as shown on the detailed list of waters visited. Miss C. M. Acland, H. G. Alexander, W. B. Alexander, Lt.-Col. I. B. H. Benn, C. H. Bentham, J. R. W. Blathwayt, H. Boase, H. B. Booth, A. W. Boyd, F. Brady, Dr. J. W. Campbell, R. M. Carey, J.J. Cash, G. H. Clegg, E. Cohen, Miss S. N. Colenso, C. L, Collenette, Dr. S. Craddock, C. P. H. Edwards, C. W. S. Ellis, J. C. S. Ellis, L. M. Emberson, W. E. Glegg, Rev. G. Gore-Skipworth, W. Hartnell, C, H. Hawes, A. G. Haworth, D. J. Hemming, Mrs. Henderson, P. A. D. Hollom, R. C, Homes, G. Hopkins, H. G. Hurrell, G. C. S. Ingram, H. R. Jasper, Miss P. H. Jefiery, Dr. N. H. Joy, H. Kenrick, J. C. Laidlay, S. Lewis, H. A. Littlejohn, B. Lloyd, Maj. J. N. Logan, Miss C. E. Longfield, Rev. C. E. Martin, Midlothian Ornithological Club, J. Moore, E.-M. Nicholson, C. Oldham, Major A. Pam, L. Par- menter, Capt. C. E. V. K. Peberdy, R, W. Pethen, Miss D. T. Raikes, B. B. Riviere, E. C. Rowberry, H. M. Salmon, H. E. Shorney, C. O. Silvers, G. Skoyles, A. R. Sumerfield, F. G. Swayne, W. Telfer, H. Tetley, B. W. Tucker, L. S. V. Venables, B. T. Ward, J. B. Watson, C. Weeks, J. W. West, J. S. Wightman, J. D. Wood, W. A. Wright. SUMMARY. 1. A sample count of slightly less than half the Great Crested Grebe population of Great Britain was made in 1935. Scottish, Welsh, Northern, Midland and particularly Thames Valley waters were included. 2. The total counted, about 1,300 birds, showed an increase of 3 per cent, since the complete census of 1931. The number of breeding pairs had fallen by 6 per cent, and there was a considerable increase in non-breeding birds. 3. An analysis by counties of the numbers of breeding pairs shows that the decreases were practically confined to the Thames Valley and that there were increases in most other areas. 4. The counties which suffered most at the height of the drought of 1933/34, receiving only 70 per cent, or less of their average annual rainfall, were likewise in south-east England, which suggests a connexion between the decrease of nesting Grebes and shortage of rainfall. Cheshire was the only county VOL. xxx] REPORT ON GREAT CRESTED GREBE. 151 outside this area to have a similar deficiency of rainfall and there, too, there were indications of a decrease of Grebes. 5. By the summer of 1935 the effects of the drought had largely disappeared and in only a few instances were Grebes reported to be adversely affected. Decreases of breeding pairs were most noticeable at reservoirs. 6. Owing to a tendency to require stricter proof of breeding in 1935 than in 1931 and to the inclusion in the sample of a high proportion of the counties where the shortage of rainfall was most acute, it is probable that over the whole country the decrease of breeding pairs, and increase of non-breeding birds is less than is indicated by the sample count. In conclusion, the effect of the drought on the Grebes as revealed in 1935 was slight. One would have expected to find a considerable reduction in the number of adults if nesting operations had been severely interfered with in the drought years of 1933 and 1934, but actually numbers were rather higher in 1935 than in 1931. The Grebe population of Great Britain would therefore appear to be in a very healthy state, ready to take advantage of more settled conditions in the future. 1935 1931 Breed Breed­ ing Non-B. Total ing Non-B. Total BERKSHIRE Pairs. Birds. Adults. Pairs Birds . A dulls (Oxford Ornithological Soc.) Aldermaston Park, Big Lake 1 0 2 1 0 2 Decoy Pond 1 0 2 0 0 0 Ascot Place 1 0 2 2? 0 4 Bearwood Lake 2/3 0/2 6 3 0 6 Binfield Brick Works 1 0 2 — 2 ?) 2 Buckland House 0 0 0 1 0 2 Buscot Lake 4 0 8 3/4 0 6/8 Buscot House Reservoir 1 0 2 1 0 2 Buscot Little Lake ... 1 0 2 1 0 2 Bulmershe, North Lake 1 0 2 0 0 0 South Lake* 1 0 2 0 0 0 Faringdon Park 0 0 0 1 0 2 Foliejon Park 0 0 0 1 0 2 Great Meadow Pond 4 5 13 6/7 0 12/14 Oakfield, Millbarn Pond 1 0 2 1 0 2 Queensmere 1 0 2 I 0 2 Silwood Park 1 0 2 1 0 2 Sunninghill Park Gt. Pond 2 0 4 1 0 2 Theale Gravel Pit ... 1 0 2 0 0 0 Virginia Water C.7 c.8 22 10 3 23 Whiteknights Lake 2/3 0/2 6 1 0 2 Wokingham, Heath Lake 1 0 2 0 0 0 34/36 13/17 85 35/37 5 75/79 •Bulmershe, South Lake. Six non-breeders were subsequently reported, in addition to the breeding pair. 162 BRITISH BIRDS. [VOL. XXX.

1935 J93i Breed­ Breed­ ing Non-B. Total ing Non-B. Total Pairs. Birds. Adults. Pairs. Birds. Adults. BUCKINGHAMSHIRE {Oxford Ornithological Soc.) Blackpit, Lillingstone Dayrell o o o 102 Black Park, Langley ... i o 2 000 Chess River, Latimer House 102 204 Claydon Park, Lower Pond 000 102 Colnbrook By-pass Gravel Pit 306 204 Rowley Lake, George Green 1 o 2 000 Shardeloes Park ...... 1 o 2 102 Stowe Park, Large Lake ... 2 o 4 102 306 Weston Turville Reservoir 3{?) 7{?) 13 -— 22 Wotton Park (2 Lakes) ... 5/6 8/10 c.20 17/18 15/17 51 • 11 2 24 CHESHIRE {A. W. Boyd) AlsagerMere 1 o 2 — o — Baddiley Mere (Reservoir) 1 I 3408 Barmere 2 o 4204 Billinge Green o o 0102 Bosley Reservoir ... 1/2 1 3/5 10 2 Cholmortdeley Castle 1/2 o 2/4 204 Combermere 7 o 14 8 o 16 Crewe Hall ... 1 o 2204 Cotebrook 1 o 2000 o 10 10 7 o 14 Doddington Park ... 1 o 2000 Elton Hall Hash ... I 2 4 0 0 0 Hurleston Reservoir I 0 2 1 0 2 Little Bad-worth Pool h 3/4 4/6 12 1 0 2 Marbury Mere, Gt. Budworth 2 0 4 6 0 12 Martrary Mere, S. Cheshire 2 0 4 I 0 2 Mere Mere ... 1 ,.'2 0 2/4 I 0 2 North Rode 1 0 2 0 0 0 New Pool, Whitegate 1 0 2 O 0 0 0 0 Norbury Booths 0 I 0 2 0 14 0 8 Oakmere 7 4 3 0 6 1 0 2 Oulton Pool 1 0 2 2 0 4 Pettypool ... 2 5 9 2 0 4 Radnor Mere 10/11 0 20/22 16 15 47 Redesmere 2 0 4 0 0 0 Rostheme Mere 1/2 0/2 4 0 0 0 Rode Heath 1 0 2 1 0 2 Quoisley Meres 3 0 6 2 0 4 Sutton Reservoir . 3 7 13 7 23 37 0 0 0 1 0 2 Tabley Mere 1 1 3 1 0 2 Tatton Mere... 2 1 5 1 0 2 Thornycroft 0 c.6 c.6 1 0 2 Tilstone Lodge Pool 10 0 20 1 0 2 Walton Reservoir . Witton Flashes 74/80 38/42 190/198 78 38 194 Winsford Top Flash VOL. xxx] REPORT ON GREAT CRESTED GREBE. 153

1935 1931 Breed­ Breed­ ing Non-B Total ing Non-B. Total Pairs. Birds. Adults. Pairs. Birds. Adults. DERBYSHIRE Kedleston Park Lakes—I. 1 0 2 0 0 0 II. 1 0 2 0 0 0 III. 0 0 0 0 0 0

2 — 4 0 — 0 DEVONSHIRE Slapton Ley 1/a 0/2 4102 Blagdon Lake, Ashwater o 00000 1/2 0/2 4 j 1 — 2 ESSEX (London Nat. History Soc.) Braxted Park 2 0 4 1 0 2 Dagenham Breach 0 0 0 1 0 2 Eagle Pond, Snaresbrook ... I 0 2 0 0 0 Gosfield Park 2/3 (?) 0 4/6 (?) 4 0 8 Great Hallingbury Park ... I 0 2 1 I 3 Lea Valley Reservoirs (13)... 7 28 42 c.24 3° 7« Navestock Park(DudbrookLakeke)) o0 0 0 1 0 2 Sewardstone Gravel Pit 2 2 6 0 0 0 Thorndon Park 1 0 2 1 0 2 Wormingford Decoy 1 0 2 0 0 0

17/18 30 64/66 33 31 97 GLOUCESTERSHIRE Cirencester Park 1 0 2 0 0 0 Tortworth Court 1 0 2 0 0 0

2 0 4 0 0 0 HERTFORDSHIRE Cheshunt 2 0 4 2 0 4 Elstree Reservoir ... 0 4 4 3 0 6 Hamper Mill Gravel Pit 5 14 24 0 0 0 Tring (4 Reservoirs) 15/20 0 30/40 25 35 «5 Wormley Bury 1 0 2 i 0 2

23/28 18 64/74 31 35 97 LEICESTERSHIRE (H. KenricK) Belvoir Fish Ponds 306 408 000 204 204 306 Groby Pool 408 306 Knipton Reservoir ... 5 o 10 5 o 10 Moira Reservoir 1 1 3 2 o 4 204 204 Stapleford Park 000 204 Staunton Harold 102 102 Swithland Reservoir 8 6 22 408 Thornton Reservoir 419204 Willesley Lake 408 204 34 8 76 I 32 o 64 154 BRITISH BIRDS. [VOL. XXX.

1935 I93i Breed- Breed­ ing Nm-B. Total \ ing Non-B. Total Pairs. Birds. Adults. Pairs. Birds. Adults. LINCOLNSHIRE Raucely Hall 1 0 2 0 0 0

MIDDLESEX (London Nat. History Soc.) Ashford Gravel Pit.... 1 0 2 0 0 0 Feltham Gravel Pit... C.4 0 c.S 4 4 12 Gunnersbury Park ... 1 0 2 1 0 2 Hatton Gravel Pit 0 9 9 0 0 0 Osterley Park 3 0 6 2 0 4 Ruislip Reservoir ... 0 14 14 4 0 8 Stoke Newington Reservoir 1 4 6 3 1 7 Teddington ... ? ? ? 0 0 0 Trent Park ,. 0 0 0 1 0 2

27 47 15 5 35

NORFOLK (Lt. Col. I, B. H. Benn and B. B. Riviere) Filby Broad 9 0 18 9 0 18 Hickling Broad 9 0 18 9 0 18 Horsey Mere 3 0 6 3 0 6 Hoveton, Big Broad 9 0 18 6 0 12 Little Broad 12 0 24 7 0 14 Snipes Water ... 1 0 2 1 0 2 Hudson Bay 2 0 4 r 0 2 Ranworth, Inner 14 0 28 22 0 44 . Outer 4 0 8 4 0 8 Rollesby Broad 19 0 38 20 0 40 Ormesby Broad 12 0 24 12 0 24 Salhouse Broad 3 0 6 3 0 6 S. Walsham, Inner & Outer C.8 0 c.i6 7 0 14 Upton Big Broad ... 2 0 4 (Not counted 1931) Woodbastwiek, Decoy Broad 5 0 10 3 0 6 Cockshoot Broad 1 0 2 (Not counted 1931) Old Hall Broad 1 0 2 (Not counted I93i) Total (excluding Broads not 1 not counted 1931) ... no o 220 1 107 o 214

NORTHAMPTONSHIRE Ashby St. Led., High P., ArmilltllSs 2 2 6 3 1 7 , Upper Lake O 0 0 1 0 2 Lower Lake I 0 2 1 0 2 Stanford Reservoir IO 25/26 45/46 C.32 0 c.44 Westhorp, Upper Reservoir O 2 2 O 2 2 Lower Reservoir O 6 6 6 6 18

13 35/36 6l/62 ,33 9 75 VOL. xxx] REPORT ON GREAT CRESTED GREBE. 155

1935 1931 Breed­ Breed­ ing Non-B. Total ing Non-B Total Pairs. Birds. Adults. Pairs. Birds. Adults. OXFORDSHIRE (Oxford Ornithological Soc.) Blenheim Park, Upper Lake 3 o 6 3 0 6 Main Lake 5 o 10 5/6 0 10/12 Bladon Water o o o 2 0 4 Clattercote Reservoir 2 o 4 2 0 4 Eynsham Hall 2 o 4 I 0 2 Kirtlington Park I o 2 I 0 2 , near Shiplake I o 2 o 0 0 Shelswell Park O i I I 0 2

M i 29 15/16 0 30/32 SHROPSHIRE Norton Mere 2 o 4 2 0 4 SOMERSETSHIRE (S. Lewis) Blagdon Reservoir ... IO o 20 12 0 24 Barrow Gurney Reservoir o C.15 c.15 O 4 4 Chew Magna o 0 o I 0 2 Chard Reservoir I o 2 O 0 0 Litton Reservoir, Upper ... I o 2 I 0 2 Lower ... I o 2 I 0 2 Marston Park 2 o 4 O 1 1 Orchardleigh 2 o 4 2 0 4

17 15 49 17 5 39 STAFFORDSHIRE Bellfields Reservoir 0 eg eg 6 0 12 Betley 3/4 0/2 8 2 0 4 Dimmingsdale, Pool Hall ... 0 3 3 1 0 2 Small Pool 0 0 0 1 0 2 Park Pool, Weston 2 0 4 1 0 2 White Sitch 2 0 4 1 0 2

7/8 c.13 28 12 0 24 SURREY Beddington Lane, North G.P 0 2 2 0 0 0 Bury Hill, Dorking... 2 0 4 1 0 2 Frensham, Great Pond 8 0 16 6 0 12 Little Pond 2 0 4 2 0 4 . 1 0 2 9 0 18 Godstone, Bay Pond 1 0 2 I 0 2 Ivy Mill 0 0 0 0 0 O ... 4 0 8 3 0 6 Mitcham Junction Gravel Pit 1 0 2 0 0 0 Penn Ponds, Richmond 2 0 4 3 0 6 ... 1 0 2 1 0 2 South Norwood Lake 1 0 2 0 0 0 Walton Gravel Pit 0 3 3 0 0 0 Carried forward: 23 5 51 26 o 52 156 BRITISH BIRDS. [VOL. XXX

1935 I93i Breed­ [Breed­ ing Non-B, Total ing Non-B. Total Pairs. Birds. Adults. Pairs. Birds. A dults. SURREY—continued Brought forward: 23 5 51 26 0 52 Weybridge Mill Pond I 0 2 1 0 2 Seven Arches I 0 2 1 0 2 Wimbledon ... 0 4 4 2 0 4 Windsor Park, Obelisk I 0 2 1 0 2 Wire Mill, near Lingfield . I 0 2 1 0 2

27 9 63 32 0 64

WARWICKSHIRE Wormleighton Reservoir 0 2 2 1 0 2

WILTSHIRE Stourton, Upper I 0 2 1 0 2 Lower I 0 2 1 0 2

0 2 0 4 2 4 WORCESTERSHIRE Bittell Reservoir, Upper C.2 0 IO IO C.2 Lower O O 6 0 12 6 3 2 8 6 10 22

YORKSHIRE 3 {H. B. Booth) Bretton Park, Upper Lake 0 0 0 000 Lower Lake 2 1 5 204 Castle Howard 2 0 4 204 Chelker Reservoir 1 2(?) 4(?) 102 Coniston Cold 1 O 2 000 Dringhouses 3 O 6 306 Eshton Tarn 0 O 0 000 Fairburn 7 O r4 16 0 32 Gouthwaite Reservoir 2 O 4 102 Harewood Park 2 O 4 204 Hornsea Mere 16 5 37 10 0 20 Malham Tarn 1 0 2 r 0 2 Rybill Reservoir 9 0 18 7 0 14 Walton Park 1 0 2 102 Wiganthorpe 1 0 2 102

48 8 104 47 0 94

BRECONSHIRE Llangorse Lake 14 0 28 13 0 26

GLAMORGAN Hensol Lake 2 0 4 2 0 4 VOL. xxx.] REPORT ON GREAT CRESTED GREBE. 157

1935 1931 Breed­ Breed­ ing Non-B Total ing Non-B. Total Pairs. Birds. Adults. Pairs Birds. Adults. ANGUS (H. Boase) Ardgarth (Lundie) ... i 0 2 (Not counted 1931) Balgavies 3 o 6 i 0 2 Duns Dish ... o o o i 0 2 Forfar 3 o 6 (Not counted 1931) Fithie i o 2 (Not counted 1931) Lintrathen ... 6 o 12 2 0 4 Lochendores... I o 2 I 0 2 Rescobie I o 2 2/4 0 4/8 Thriepley 2 o 4 o 0 0

13 o 26 7/9 0 14/I8 (excluding waters not counted in i J3i)

FIFESHIRE Lindores 3 o 6 8 0 16 Kinghorn Reservoir 2 2 6 I 0 2

5 2 12 9 0 18

KINROSS Leven 12 o 24 8 0 16

PEEBLESSHIRE Portmore Reservoir ... i o 2 I o o o

PERTHSHIRE (H. Boase) Clunie 2 o 4 I O 2 Craiglush I o 2 o O O Fingask I 0 2 (Not counted 1931) Lowes 2 o 4 o 0 0 Marlee 4 o 8 2 0 4 Ochtertyre ... o o o I 0 2 Rae I o 2 I 0 2 Stormont 3 o 6 2/3 0 4/6

13 o 26 7/8 o 14/16 (excluding Fingask) MIDLOTHIAN (Midlothian Ornithological Club) Bavelaw Reservoir 0 0 0 1 0 2 Cobbinshaw Reservoir 0 2 2 2 0 4 Gladhouse Reservoir I 2 4 1 0 2 Harperrig Reservoir 0 I 1 0 0 0 Thriepmuir Reservoir 0 2 2 0 0 0

I 7 9 4 0 8 158 BRITISH BIRDS. [VOL. XXX.

CORRECTIONS AND ADDITIONS TO THE GREAT CRESTED GREBE ENQUIRY, 1931. Several inaccuracies in the report on the Great Crested Grebe Enquiry of 1931 [British Birds, yd. XXVI., pp. 62/92, 102/131, 142/195) have come to light since the publication of the list of corrections and additions at the end of the report. These are as follow :— p. 69. Buckinghamshire, Wotton Park : Two birds were seen, but probably none nested in 1931 (cf. Report of the Oxford Ornithological Society for 1932, pp. 58/59). p. 73. Essex, Navestock Park and Dudbrook Lake are the same locality. Dudbrook Lake should therefore be deleted from the list of waters unoccupied in 1931 (W. E. Glegg and B. T. Ward). p. 76. Leicestershire, Stapleford Park. Two pairs nested in 1931 and not four pairs as given in the report (H. R. Jasper). p. 79. Norfolk : Upton Broad and Woodbastwick Cockshoot and Old Hall Broads were not reported on in 1931. They held 4 pairs in 1935, as is usual (B. B. Riviere). pp. 79/80. Northamptonshire : W. B. Alexander has drawn attention to the dates of occupation of the following waters given in Lilford's Notes on the Birds of Northamptonshire. Blatherwycke : 2 pairs (at least one bred), 1886. Canon's Ashby : Pair shot in April, 1886. : Bred in 1885 and 1886, 5 in April, 1890, 4 in March and one pair bred 1891. Reservoir : 10 in April, 1884. Welford : Pair in June, 1884. p. 89. Yorkshire.: Renishaw Park, Sheffield: One pair bred in 1931 and for many years previously, but not in 1930 (H. B. Booth). p. 289. Midlothian, Scotland: Thriepmuir and Bavelaw reservoirs adjoin and sometimes both are called Thriepmuir. In 1931 one pair bred on Bavelaw, none on Thriepmuir (Midlothian Ornithological Club). These alterations leave the figure for the total number of Great Crested Grebes in the country in 1931 unchanged.