BRAAKSMA S & BRUIJN O DE (1976) New data on Barnowls Tyto alba in The Netherlands. LIMOSA 49 (3): 135-187.

Barn Owl Tyto alba In 1962 the number of breeding pairs of the Barnowl in the Netherlands was estimated to be about 3000 (Honer 1963). More recent information, gathered during personal visits to at least 2500 churches, farms, castles, windmills and other potential breedingplaces was added to the communications of about 3000 farmers, priests and other people and to the data in about 650 letters and more than 100 published reports on this subject. These data suggest that it is likely that in former years, when plagues of common voles still occurred on a large scale in our country, the Barnowl-density was even higher. In spite of the factthat Honer's basic material was not availablc and exact information on the occurrence in former days proved to be rather hard to get we managed to register 628 certain and 673 doubtful breedingplacesbefore the severe winter of 1962-1963. In Table I these data are compared with the numbers of breedingpairs registered in the periods of 1963-1968 and 1969-1974. Table 2 (in dutch) gives information concerning the completeness of the census in different parts of the Netherlands. Regarding the incompleteness of our census, added to the faCt that Honer seriously underestimated the density of the Barnowl on our diluvial soils, we suppose that the real number of breeding-pairs'before the severe winter must have been at least 3500 in years when rodents were abundant and at least 1800 pairs in years with a very low rodentlevel (Table 3). The notorious winter of 1962-1963 is known to have caused severe losses to European bird-life, including the Barnowl-population (e.g. Glutz von Blotzheim 1964). We suppose that less than 30% or perhaps even less than 20% of the dutch Barnowls managed to survive. Only a few of.them were fit enough to breed in 1963. In 1964 however there was a notable increase of the number of breeding-cases. Under normal circumstances birds with an average clutchsize of about four eggs - like the Barnowls in our country have ~ must be able to recover from losses like the one in 1963 within 6 years with mild winters. In Holland we have had no severe winters since 1963. In spite of this, the results of a census during the period of 1967 till 1974 made it clear that a total of about 800 breedingpairs is the highest possible estimation during any of those years. The highest level was reached in 1968, a year when common voles were abundant on several places. Then the number of breeding pairs was estimated to be somewhere between 500 and 800. In 1971, 1972 and 1974 the common voles again reached a plague-level on several places. Our counts suggest that only 300 till 500 breeding Barnowls were present in these years. In 1969 and 1973, on most places, only a few common voles occurred. In 1969 the number of breeding pairs amounted 200 till 400. In 1973 only ISO till 250 breeding Barnowls were still present. Hence it seems to be clear that - apart from the nonnal annual fluctuations llnder influence. of climate and the rodents-cycle - there has been a considerable general decrease of the Barnowl-population in the Netherlands. The distribution-maps show that especially in the western part of the country there are hardly any breeding Barnowls left. The decrease is also remarkable in the grasland-areas in other parts of the Netherlands. There are several possible reasons for this drastic decline. The most important factor however, probably is a change in the feeding possibilities. Owing to modern agriculture vole plagues no longer occur in many areas where these animals used to be periodically abundant in former days. Perhaps even worse for the Barnowls is the fact that at present most farmers keep their grain-harvest only for a very short time in their own barns. The modern central storingplaces are so well closed that hardly any rodents can live there. The common shrew was and still is the second topper on the Bamowls diet-list in most parts of the Netherlands. However, its numbers have been seriously reduced by the fact that so many hedges have been cleared. The pellets provided such a huge amount of information about local differences in the Barnowls food in various parts of the country that one of the authors of this article is preparing a special paper on this subject. This paper will probably be published in 1977. Unfortunately for the Barnowls, besides lack of food, there are still several other factors which at least are responsible for a part of the decline. One of the first things, people use to mention in this regard is the use of organo-chlorines and other toxic chemicals for agricultural and horticultural purposes. Personally we also believe that several hundreds or perhaps even thousands of Barnowls have been poisoned during the past ten years. Yet we have hardly any real evidence for this point of view, as only a few Barnowls and Barnowl-eggs have been investigated on the occurrence of D.D.T. and other poisons. Besides the analysisresults mentioned in Tables 10 and .II, we can only refer to some other results of recent investigations, like one on the mercury-level of five Barnowls found dead in 1968_1970. We thought that it might be useful to compile all incidental information we got on death-causes. The results shown in table 9 do not have any further pretention than giving a review of 760 reported death-causes. Of course these data have only a very low comparable value as is being shown by the very low number of winter-victims in 1963 in comparison to the high number of stuffed Barnowls in that year (See Fig. 3). This is an unavoidable result of the fact that we only used the information that seemed to be trust-worthy and neglected several hundreds of doubtful death-causes. Nevertheless we can use them as an indication of what has been going on before and after 1962. It was for instance shocking for us to learn how many Barnowls were reported as deliberately killed, - the bulk of them in our own country, where these birds have been legally protected since 19l2! The real figures must be even much higher, because many people are wellaware of the fact that killing a Barnowl can cause serious trouble to the tresspassers of the law, so they don't easily talk about it. The desire to possess a stuffed Barnowl proved to be the main reason of most of the reported killings. With a total of about 10.000 legally stuffed specimens (see Fig. 3), this bird is the most stuffed species in the Netherlands since World warII. To avoid misunderstanding we must add that no doubt only a small percentage of these Barnowls stuffed by official registflred taxidermists have been killed deliberately. On the other hand however we have the impression that many victims of human persecution have been stuffed illegally and that a rather great part of the Barnowls that .have been killed because they made such horrible noises of because their droppings and their pellets built such a mess has been thrown away. The same happened to some Barnowls that were killed in poultry-farms because they started a panic amongst the hens (we heard that in one farm nearly 100 hens were. killed in this way). Alarming is the very rapid increase of the birds being reported as traffic-victims. We are quite sure that besides the food-position and the dangers causes by toxic chemicals and direct persecution, traffic is the most important factor in the general decline of this species. The increasing number of traffic-victims is likely to be closely related to the increased number of cars and to the fact that several roadsides built suitable habitats for small mammals. Amongst the less important death-causes mentioned in Table 9, the fact that 22 Barnowls have been registered as drowned is perhaps the most curious one. His still completely unclear whether these owls have lost their balance while they were looking for food or while they were trying to drink. There is also a possibility that the reflection of the birds by the water-surface plaid a role. There is a possibility too that they were thirsty because they had consumed poisoned preys or baits used by game-keepers or hunters who intended to destroy crows or jays. Amongst the losses caused by wires, those by bobbed wire are the worst. Hunting Barnowlsand also Tawny owls and long-eared owls do not seldom hit the bobbed wire with one wing while they are hunting. So they get trapped and die in a horrible way. Locally the Barnowl-density may have been influenced by some interspecific competition with Tawny owls. This competition may include both food- and breeding-habitat. The second factor is perhaps the most important one, as shown in table 12. Some competition for breeding-places may also occur with Kestrels and Jackdaws. Competition with other Barnowls is supposed to be only of local importance in times when food is very scarce. Another vactor that may be responsible for local decrease is the fact that several hundreds of breedingplaces in buildings got lost because people fenced every possible entrance for birds. No doubt many Barnowls succeeded in finding other localities, but at least some of these were far less suitable than the original ones. Besid~s it occurs that the entrances are being closed while the birds are still in the building, so that they are doomed to starve (Table 9). According to Honer's investigations coccidiosis and other deseases hardly have any influence on the mortality of the Barnowl. The increased risk caused by traffic, poison etc. may, together with the lack of severe winters since 1963, be responsible for a remarkable change in the annual mortalitypattern since Honer's publication (compare his figures with those in Table 8). The probable differences in mortality between birds ringed as nestlings and those ringed as fullgrown are not based on sufficient data to allow areliable comparison. As the reproduction-rate is a very important factor e.g. in regard to the possibilities of the Barnowls to recover from local losses, we paid much attention to the clutch-size and the breeding-results. Although we have several data of clutches of more than 6 eggs, the average of 599 clutches after 1963 proves to be only 4,0. This is 0,2 less than the average of 106 clutches found before that year. When we compare the final breeding-resutls of 39 nests before 1963 withthose of 452 more recent breeding-cases, we see that the average number of young decreased from 3,2 till 3, I. However these data are not quite comparable in an proper way because they partly concern different breeding-places and besides there may be a rather. strong influence of the usual 3 to 4 years cycle of the common voles (compare Tables 5 and 6). In order to see whether there were any differences in age-composition 132 recoveries of birds ringed before 1963, have been compared with 221 recoveries of birds ringed after that year. In both cases mean life-expectation proved to be low, as only about 13% of the birds were recovered after their second year (Table 7). A comparison with 999 recoveries of Barnowls ringed in Switserland before 1963 (Glutz von Blotzheim 1964) shows that swiss Barnowls have a much higher life-expectation: 26% of the swiss Barnowls were recovered after their second year. This high life-expectation may be a necessity in regard to the losses caused by severe winters. Our oldest Barnowl was at least 18 years old, the eldest swiss one reached the age of 21. The available recoveries show that dutch Barnowls seldom fly far: 87% ofthese birds were reported at less than 100 kilometers from the ringing-place. A comparison between the distances of the recoveries before and after 1962 (Table 13) shows some differences. It seems likely that these differences have at least partially been caused by the smaller population-density in combination with the mild winters during the past 12 years. Besides some long distancerecoveries in Germany there are 13 recoveries of dutch Barnowls in France and even one in England, one in Spain, one in Switzerland and one in Poland. On the other hand we know that 4 Barnowls ringed in Switzerland have been recovered in our country. There seems to be no special trend in the direction our Barnowls use to fly. This behaviour may be very useful in filling up open places in suitable breeding-habitats. The only possible influence on the dispersal of ringed Barnowls may be caused by big water-surfaces and high mountains (Sauter 1956). As there is at least some exchange of breedingbirds with surrounding countries, a short review has been given of the present status in these countries. The chances of a short-term invasion of many foreign breeding birds seem to be very small as a general decrease has been reported in Belgium and Germany Gust as in England). As breeding-places dutch Barnowls prove to prefer farms and barns. Churches are second on the list (Table 4). Hence we ought to accept the english name of this species in stead of the dutch name Kerkuil - meaning Churchowl.Other important breeding-places in our country are castles. breeding-boxes, windmills and chimneys of houses. The number of breeding-cases in hollow trees and on other natural breeding-places is very low, in comparison to England, where in 1932 about 43% of 915 registered breeding pairs were found in hollow trees (Haver- schmidt 1934). As there may have been a considerable urbanisation in England too, it would be very interesting to compare these 1932-data with recent ones! Regarding the protection-possibilities it is hopeful that an apparently increasing part of our Barnowl-population tends to breed in breeding-boxes. As a result of our advertising at least 250 new special breeding-boxes for Barnowls have been placed during the last 8 years. In 41 of them succesful breeding cases have been estimated (compare Table 14). Other recommended measures to offer the Barnowl more protection are: propaganda-activities in order to make Barnowls more popular; a ban on stuffed owls for other than scientific purposes; a restriction of the use of certain pesticides; efforts to raise the amount of small mammals in naturereserves; conservation and reconstruction of hedge-rows; removal of fences that keep birds out of buildings, a continuation of the present reward-system of 25 dutch guilders? for succesful breeding-cases of Barnowls in buildings; giving food to Barnowls during long periods of snow, and to avoid disturbance by birdwatchers on the breeding-places. 13.

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