annual cycle of the Little Owl

What is it about?

In 1982-- 1984, field and aviary observations of Little Owls were made in the Lower Rhine area (district of Kleve). Locomotory activity was studied in a flight cage situated outdoors under natural light conditions and by radio telemetry in the field. The locomotory activity of a caged breeding pair was highest during the nestling and fledging period (June/July), as it is in free living birds. When an unpaired male was caged, highest values were registrated in October/November. Little Owls showed least activity during winter (November-January) and during the main moult period (fig. 1 and 2). -- The seasonal pattern of calling activity was determined by means of systematic field studies during the first two hours after sunset, at the time of the daily maximum. Vocal activity was highest during the courtship period, in March/April (fig. 3). -- Mean monthly body mass of adult males varied between 166,9 +8,3 g in July and 237,8 _+24,8 g in January. Masses of adult females varied between 172,9 _+17,4 g in July and 249,8 _+18,3 g in December (fig. 4 and 5). Whereas the mass of the males decreased from January to July, females' mass increased in the pre-laying period. In April and May females were significantly heavier than males. -- Over a period of 2 years records of the food intake of birds in a flight cage resulted in a yearly food consumption about 88.300 kJxbird -1. The highest values were reached in October/November, the lowest values were recorded from December to February (fig. 6). -- Ringing recoveries from NW-Germany indicate two mortality peaks: a summer peak (June/July) associated with the stress of the breeding season and a winter peak (January/February) (fig. 7). -- Although territorial aggressiveness is recognizable throughout the year, the seasonal occurence of the most frequent calls indicate a first phase from August to November motivated mainly by territorial behaviour, and a second sexually motivated territorial phase, which can be subdivided into three periods (pair formation November/December, courtship January/February--end of April, and breeding end of April--July. The results clearly demonstrate that an energetic bottleneck occurs in July. It is associated with the stress of rearing the young and the beginning of the moult, both incurring higher energy expenditure. The winter mortality peak, however, is caused by exceptionally high mortality rates in extraordinarily severe winters. Both fattening in October/November and reduced energy needs from December to February enable Little Owls to survive 2--3 weeks of fasting during winter. The annual timing of breeding, moult and fat deposition are discussed in connection with the seasonal variation of food abundance.

Featured Image