Kestrels' nest at Nencki Institute

View from the nest:


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Facts about the nest of kestrels in Nencki Institute
GPS position of the Nencki Institute: 52.213333, 20.984198 0r 52° 12' 48" N, 20° 59' 3" E
The wall with nest faces west.
Height of the nest above ground is 16.5 m.
The main building of the Nencki Institute has been finished in 1956. Two rooms at the uppermost story were furnished with ventilators, removing toxic fumes created during biochemical experiments in hoods installed in these rooms. Ventilators were fit into round holes of the diameter of 35 cm penetrating the 40 cm thick wall. In mid 1960-ies a different system of ventilation of chemical hoods was installed in the Institute, including those two rooms and the ventilators were removed from external walls. Holes were left open from the outside and small revision doors were installed inside rooms, enabling access to the space from inside the room. Walls of the Institute are built of bricks that in the central part of the short tunnel do not fit the round shape of the external opening, leaving more space in the central part.
From the corridor windows in the Southern wing of the Institute it is possible to see the inside of the nest with binoculars. At present second, external camera was placed there.

History of Kestrels’ nesting in the Nencki Institute
The first confirmed year of kestrels’ nesting in that place is 1972, but it is claimed that at that time “they were present there since a few years”. At that time it was one of only a few kestrel’s nesting sites in Warsaw. Since then kestrels successfully nest there every year. Kestrels had chosen the more southern of the two identical holes and always nest there, although they visit the other site too.
Since 1994 Dr Kris Turlejski started observations of the nesting kestrels and collection of kestrels’ pellets and feathers at the nest. Since 1996 Łukasz Rejt from the Museum and Institute of Zoology, Warsaw started his project of investigating biology of kestrels nesting in Warsaw and cooperated with Dr Turlejski. He later defended his PhD on that topic. Two Master degrees in Biology based on observation of the Nencki Institute nest were also granted and several papers published.
In 2001 black-and white analog camera was installed inside this nest (as well as in three other nests in Warsaw), allowing for recording the nesting activity of kestrels. In 2004 the Institute installed external shelves in front of both openings and internal frame with glass on the internal inside of the nest-hole, to prevent kestrel’s pecking on the camera. This year the camera was changed to the color and digital one, and another, external camera added. Views from the cameras are publicly available at the Nencki Institute page. This is a common project of the Nencki Institute and the Institute of Zoology. 2008 is the 90th anniversary of the existence of the Nencki Institute.


Timing and other facts concerning our kestrels’ breeding activity
Kestrels first appear by the nest between mid-January and mid-March. Most of the time males are first. Several times a kestrel (either male or female) wintered by the nest.
In March the returning kestrels have to stand mass attacks of jackdaws and rooks wintering in Warsaw. Later contests with local jackdaws, magpies and crows gradually vanish and are rare at the period of egg-laying and later.
Almost every year there is an attempt of a take-over of this nest by another pair, single male or female. Males never attack contesting females and vice versa. Fights of males can be fierce, they may even fall on the ground fighting. Success of the contestor(s) is about 20%.
Copulations start 2-4 weeks before the first egg is laid. First eggs are being laid from late March to late May.
Female starts to incubate eggs only after 3-4 are laid. Male changes her for short periods, when the female eats the food brought by the male outside.
Number of eggs: lowest observed – 4, usually 5-6. Record: 7 in 2007. Clutch of 7 eggs is quite rare in kestrels. In Warsaw only a few cases were noted in over 500 nests revised in the last 15 years. In rural parts of Poland 8 eggs in one nest were found twice, but it was not clear if it was not due to the take-over of the nest with eggs by a second pair.
Over 90% of eggs hatch.
Division of work: most of the time female guards the nest and male brings food for chicks and female until they start fledging. Then female may start hunting too, but it is not obligatory.
Staple food: depending on the pair, either voles (prevailing) or sparrows. Sparrows, majority of them young, are caught in the town. Voles live only in the fields and meadows, several kilometers from the nest. During the last two weeks of nesting, each chick consumes 3-4 voles a day. This means that at that period the male has to fly 200-300 km a day only to commute between the nest and hunting grounds. Other victims: blackbirds, swifts (weakened, caught on roofs), mice, shrews, moles.
Number of successfully fledged young: 2-7 (average 4-6). Occasionally a chick dies for unknown reasons. Dead chicks are dismembered by the mother and fed to siblings.

Unusual observations on our kestrels

In 1998 the male disappeared (probably died) when the chicks were 2 weeks old. After 2 days of waiting, the female started hunting. Out of 5 hatched chicks only two survived.

In 2003 when the chicks were about 3 weeks old and none of the parents was around a jackdaw entered the nest twice, trying to kill young kestrels. They defended themselves successfully with their talons, until the female returned.

In 2004 March was unusually warm and the first egg was laid in the end of March, but then winter returned and for the next 2 weeks there was thick snow cover and temperatures below the freezing point. Kestrels stopped egg-laying in that period and commenced it afterwards, eventually laying 5 eggs. All eggs hatched and all chicks fledged. As the first egg was exceptionally white, it was easy to recognize. The chick hatched from that egg as the last one, and was smaller than usual. The female took care to feed it too, as it was too weak to successfully fight for food.

In 2005 another pair tried to establish their nest in the second nest hole of the Institute. Constant territorial fights between pairs resulted in laying only 4 eggs, from which only 2 chicks hatched. The other pair laid 3 eggs and abandoned the nest.