IJZENDOORN ALJ VAN (1948) The Breeding birds of the Wieringermeerpolder in 1947. LIMOSA 21 (2): 41-69.

The "Wieringermeerpolder" is a low-lying area reclaimed from the "Zuidersea" (Zuiderzee) in 1930. These 200 square kilometres (= 20.000 ha = about 50.000 acres) were first studied by Van D 0 b ben. in 1931, the year in which the entire polder had been drained. He found 7 species breeding then. viz. Common Tern. Redshank. Ringed Plover. Kentish Plover, Little Tern, Avocet and Oystercatcher. The next year 0p de Coul could prove only 6 species as certainly breeding: an addition was the Arctic Tern (which disappeared again in the following year), but the Oystercatcher and the Ringed Plover did not nest then. There were about 5 dubious breeding-birds. In 1933 the area was not investigated. In 1934 Lapwings and Yellow Wagtails were added to the list by Van Dobben and Black-headed Gull and Short-eared, Owl by Schaank.
      Schaank succeeded in getting a list of about 32 breeding species in 1934. Some new species were: Starling, Reed-Bunting, Crested Lark. Meadow-Lark. Meadow-Pipit. White Wagtail, Reed-Warbler. Swallow. Sand-Martin. Cuckoo. Sheld-Duck, Little Grebe, Moorhen and Coot. In 1936 Linnet. Great ReedWarbler, Icterine Warbler, Whitethroat. Garben-Warbler, House-Martin. Kestrel. Garganey. Great Crested Grebe, Wood-Pigeon and Phesant were some of the birds added to the list.
      Exactly 10 years ago, in 1937 the number of breeding species had increased to 48. The total number of breeding species in 1947 was 57. Yellow Bunting. Red-backed Shrike, Wheatear, Teal. Little Grebe and Ruff were breeding birds 10 years ago, but could not be found as such now. Little Grebes may have been affected by the series of severe winters in the early forties and are also certainly handicapped in their return through the scarcity of Phragmites communis in the polder. The Ruff is presumably gone in consequence of the improved draining of the polder. The factors that affected the disappearance of the other 4 species are unknown.
      Entirely new breeding birds were Carrion-Crow. Jay. Spotted Flycatcher and Stock-Dove. The arrival of these species was already predicted last year. as the forested parts begin now to get suited to their requirements. The first 3 species were very scarce. though. Only the Stock-Dove nested in somewhat greater numbers (10-15 pairs). The latter species preferred to nest in the ruins of farms and barns. which are the remnants of the destruction wrought through the unnecessary flooding of this polder by the Germans in the spring of 1945. (For the consequences of this flooding I may refer to my last year's paper).
      In 1947 I spent about 120 hours in the polder, customarily visiting it at least twice a week, mostly for 2 or 3 hours. (See table 1, p. 41 in which the first column gives the dates from March to August and the second the numbers of observational hours per each visit). I also got much information from 2 other "birders'!. About 800 families have again returned to the 3 Villages and the farms. which are being rebuilt now.
      The most important crops in 1947 were winter-wheat (2417 ha), flax (1976 ha), sugar-beets (1477 ha). seed-potatoes (1460 ha), summer-barley (1395 ha) and oats (1284 ha) (see table 2. p. 42).
      The marginal woodland along the most Western road of the polder. the Waarden Groetweg. an area of approximateIy20 ha (= ± 50 acres) has been planted in 1936 and 1937 and has a great variety of trees and shrubs such as poplars. ash. plane-trees. sycamores. hawthorns, alders and birches. The only remnant of the splendid "Robbenoord" wood in the North Eastern part of the polder was a Willow-wood of approx. 25 ha. There were some other small poplar-woods, totalling about 4-5 ha, in the polder.
      The reafforestation of the polder was continued and some 15 ha were planted with sycamore. beech. birch, alder etc. near the "Dijkgat" (on the sandy plain that owed its existence to the blowing-up of the dyke and the following inundation).
      An attempt was made to compute the total number of breeding pairs in 1947. This was done by counting the singing and territory-defending males anywhere and at any visit. by counting the foraging or straying flocks (Wood-Pigeon, Linnet. Stock-Dove etc.), by the gathering of data on nests and on the young seen. The data obtained in this way were a basis to estimate the total-number of breeding pairs. The' resulting figures are, of -course. by no means exact. but they do certainly give a much better insight in the real population than the customary terminology of "rare, numerous". etc. The figures given in table no 3. on p. 63 represent the minimum numbers of breeding pairs mostly in round numbers. So we come to the conclusion that there were about 8600 breeding pairs in the Wieringermeer. This is on the average ± 0,43 breeding pairs per ha. This average is low. compared with the figures that we are used to find in woodland areas.
      Hickey (1943) gives a table on some North American habitats that have been censused and if we may equalize his 4 "adults per 10 acres" to my 2 "breedingpairs" per 10 acres (= 4 ha), then we see a similar density in a "Sandy field, in Wisconsin, abandoned farmland". and a nearly corresponding density of 4,4 ad. per 10 acres in a "Prairie pasture in New Mexico" and of 4,6 ad. per 10 acres in a "Prairie. in Oklahoma". - This comparison might have some value, though further details about the American habitats mentioned in the table are lacking.

Some other interesting points are:
A single breeding-case of the Jay (Garmius giandarius) in a little willowwood in the polder. a habitat seldom if ever chosen in Holland. There is evidence that the Great Reed-Warbler and the Reed-Warbler don't like to nest in the same reed-beds. The Great Reed-Warbler is indeed an agressive bird in its domain.
The lcterine Warbler was the dominant species in the wood-land edge along the "Waard- en Groetweg" , It appeared to be about 5 times as numerous as in "Het Bosch" at Amsterdam (Sluiters. 1943),
Non-breeding Swifts were regulary seen during the season. They appear to be one-year-olds; according to a paper by S v a r d son (1948) non-breeding migrating Swifts are very numerous on the Swedish Isle of Öland.

Long- and Short-eared Owls, Kestrels, Marsh- and Montagu's Harriers nested again in the polder, totalling ± 10 pairs, contrary to the situation in the previous year. when neither Owls nor Birds-of-prey were found to be breeding, This increase is undoubtedly due to the abundance of meadow-mice (Microtus arvalis). which formed their staple-food. A large clutch (of 7 eggs) of a Long-eared Owl might also have been "'caused" by this abundance of Microtus. Non-breeding Kentish Plovers were seen in a flock near the above-mentioned "Dijkgat".
      A case of extreme tameness of the Avocet is recorded, This tame Avocet wore a ring, which appeared to be Danish; though the inscription was not well readable owing to wearing. Two Gull-billed Terns were seen. on 20th June. but they disappeared again the next day. Near the "Dijkgat' there were again small colonies of Little Terns, Common Terns, Black-headed Gulls, Kentish, Little and Ringed Plover and Avocets.

The Quail (Coturnix coturnix) was very numerous this year. This irruption was also noticed in other parts of the country and also in Belgium, England and Switzerland. An estimation of ± 500 calling cocks is based on many nocturnal and day-light counts. The Quails suffered from the "mechanisation" of this polder: many nests, and also incubating hens, were injured or killed by flax-reaping machines and mowing-machines. The wish is expressed that other Dutch "polders'" will also be better investigated and censused, so as to get more information on the problems that have arisen.

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