Danske duehøges populations- økologi og forvaltning

English summary
Following the legal protection of goshawks in
1967 the population of breeding goshawks in
Denmark increased in the 1970s and 1980s, but
in recent years the number of breeding goshawks
has declined in several parts of Denmark.
The breeding population in Vendsyssel thus increased
from 31 pairs in 1977 to 72 pairs in 1994,
after which year it declined again. Based on 24
years of data collected from the goshawk population
in Vendsyssel, this report presents detailed
analyses of the population ecology of the goshawk.
The analyses reveal the primary factors
regulating the population, and identify the reasons
for the observed population decline after
1994.
Goshawk reproduction
The age of the breeding female in relation to the
number of young raised was known for 951
breeding attempts, while the age of both the
male and female was known for 561 breeding
attempts. The number of fledglings raised per
breeding attempt increased with the age of both
the male and the female, but only for females
could a detailed analysis of this age-dependent
relationship be conducted. The annual production
of fledglings increased with female age from
1 to 7 years of age, whereupon it declined. Previous
breeding experience did not influence the
number of fledglings produced by individual
females, and poorly performing females apparently
survived with the same probability as high
performing females. The most likely explanation
for the age-dependent reproductive performance
in the goshawk population appeared to be
age-related improvements in competence, such
as foraging efficiency.
Influence of laying date and
weather on goshawk reproductive
performance
In the goshawk clutch initiation took place between
24 March and 2 May, and the mean laying
date was 8 April. The timing of egg laying
depended on female age and mean temperature
in February/March. First-year females initiated
their clutches considerably later than secondyear
and older females. An effect of senescence
showed in females older than nine years as a
relatively late laying date. In years with high
mean temperatures in the pre-laying period
(February/March), the females commenced egg
laying significantly earlier than in cold years.
The number of young raised to fledging was
dependent on female age, laying date and the
temperature in May. The timing of breeding was
thus crucial for the reproductive success in the
goshawk, as the number of young produced
declined as the season progressed. High temperatures
at the time of hatching and in the early
chick period (May) had a positive effect on the
reproductive output of the goshawks.
Dispersal of the goshawks
During 1979-1998, a total of 1,709 goshawk nestlings
were ringed within the study area; of these
206 were later recovered (recovery rate: 12.6%).
There were no sex differences in the recovery
rate, nor in the age at recovery. Most recoveries
of ringed goshawks were reported from near
human settlements, with a large proportion being
recovered near pheasant pens, pigeon lofts
and chicken runs. Young of the year constituted
71% of the goshawks recovered near pheasants,
pigeons and chickens kept by humans.
Most goshawks (78%) were recovered less than
40 km from their natal nest, and the goshawks
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