A1 Journal article – refereed
To breed or not to breed: drivers of intermittent breeding in a seabird under increasing predation risk and male bias

List of Authors: Markus Öst, Andreas Lindén, Patrik Karell, Satu Ramula, Mikael Kilpi
Publisher: Springer
Publication year: 2018
Journal: Oecologia
Journal name in source: Oecologia
Volume number: 188
Issue number: 1
ISSN: 0029-8549
eISSN: 1432-1939


Intermittent breeding may be adaptive for long-lived species subjected
to large accessory reproductive costs, but it may also reflect reduced
adaptation to the environment, reducing population growth. Nevertheless,
environmental influences on breeding propensity, particularly that of
predation risk, remain poorly understood and difficult to study, because
non-breeders are typically not identified. Female eiders Somateria mollissima
from the Baltic Sea provide an excellent testbed, because nesting
females have been exposed to intensifying predation and growing male
bias that may increase female harassment. We based our study on
long-term data (14 years) on females captured and marked at the nest,
and females individually identified at sea irrespective of capture
status. We hypothesized that breeding propensity decreases with
increasing predation risk and male bias, and increases with breeder age.
Consistent with our hypotheses, females nesting on islands with higher
nest predation risk were more likely to skip breeding, and breeding
probability increased with age. In contrast, the steep temporal decline
in breeding propensity could not be reliably attributed to annual adult
sex ratio or to the abundance of white-tailed sea eagles (Haliaeetus albicilla),
the main predator on females, at the nearby Hanko Bird Observatory.
Breeding probability showed significant consistent individual variation.
Our results demonstrate that spatiotemporal variation in predation risk
affects the decision to breed and high incidence of non-breeding was
associated with low fledging success. The increased frequency of
intermittent breeding in this declining population should be explicitly
considered in demographic models, and emphasis placed on understanding
the preconditions for successful reproduction.

Last updated on 2019-29-01 at 14:45