BOERSMA E, GROEN, LG,VOOUS, KH & WIGHT, HJ (1987) The first Tengmalm's Owls Aegolius funereus in the Netherlands. LIMOSA 60 (1): 1-8.

After the report of a young Tengmalm's Owl found dead in 1971 in the State Forestry Gieten (Groen & Voous 1973), which was the first record of this species in the Netherlands, up to four singing and apparently territory-holding males have been found in these forests in 1973-80. In the same period another minimum of one and a maximum of six males have been counted in adjacent forestries. Top years were 1976 and 1977 with totals of at least nine singing males each year. The downy young found in September 1971 was somewhat more than half grown and was certainly still dependent on its parents. It must have been raised in the forest where it was found. Late April 1974 a Tengmalm's Owl was found in an old nesting hole of a Green Woodpecker Picus viridis in a gnarled poplar. It was disturbed probably by a squirrel which had lived in a woodpecker hole a little higher up in the tree and had filled up the owl's nest with 3 eggs with its own wealth of nesting material. On 29 March 1977 a Tengmalm's Owl was found occupying an old Green Woodpecker's nest in a poplar among a 50 year old thicket of mainly spruce and fir. A meter higher up in the tree a Green'Woodpecker occupied another hole and apparently raised its young. Although the sitting owl was seen to be fed by its partner on several occasions, the nest was found abandoned on 30 May after at least 54 days of incubation; on 1 June the nest proved to contain one undeveloped egg only. Throughout the years numerous old nesting holes of Black Dryocopus martius and Green Woodpeckers in pines, beech, and poplars inspected for the presence of Tengmalm's Owls were found to be occupied by Stock Doves Columba oenas and Jackdaws Corvus monedulao None of 18 nesting boxes erected in the forests has been occupied by Tengmalm's Owls; possibly the entrance holes of 6'12 em were too narrow or too uncomfortable. Simultaneously with the top seasons in Drenthe (1976, 1977) Tengmalm's Owls have been recorded in at least three localities in the province of Noord-Brabant, singing night after night, but no nests or young have been found. A Tengmalm's Owl ringed as a nestling 8th May 1975 in the Liineburger Heide (north FRG), found dead 15th October 1975 at Farmsum (Groningen) may indicate the origin of Tengmalm's Owls occurring and nesting in Drenthe. The gradually maturing 30-50 years old state forests in the province of Drenthe, in which a variety of indigenous and exotic coniferous trees predominate and in which numerous nesting holes of Black and Green Woodpecker provide potential nesting sites, seem to have favoured the temporary establishment of Tengmaim's Owls, which elsewhere is characteristic of boreal forest types. Its arrival seems to have coincided with a top in the bank vole fluctuation cycle. When on 13 November 1972 a storm of hurricane force caused havoc in the Drenthian forests, mainly falling exotic coniferous trees, the resulting open patches and windfalls provided ideal habitats for bank voles and other microtine rodents (Microtus arvalis found in the owl's pellets). Tengmalm's Owls may have been favoured for a couple of years too. After the breakdown of the vole populations, Tengmalm's Owls disappeared rapidly. The appearance of Tawny Owls Strix aluco in 1978, up to that time unknown in these types of relatively young and densely planted forest, may have accelerated Tengmalm's Owls' decline. At the same time Goshawks Accipiter gentilis had increased as breeding birds and may have preyed on Tengmalm's Owls too, but there is no proof of either species having actually caught a Tengmalm's Owl. After the building up of attractive vole populations in the Drenthian forests some time in the future and a simultaneous decline in the forest of west central Europe, Tengmalm's Owls may be expected to temporarily reappear in the Netherlands. Tengmalm's Owls Aegolius funereus

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