Does intense herbivory from microtine rodents induce production of plant estrogens in the spring food plants of willow ptarmigan Lagopus l. lagopus?

Some plant secondary compounds show estrogenic effects that have negative influence on reproduction in mammals and birds. In northern Fennoscandia microtine rodent populations show cyclic density variation with peak and crash years. The production of willow ptarmigan chicks is always low in microtine rodent crash years, which may indirectly be caused by poor parental behaviour. We have investigated if intense herbivory from microtine rodents induce production of plant estrogens in the spring food of willow ptarmigan. We could by means of chemical analysis of plant forage not demonstrate production of plant estrogens, nor any effects on weight of uteri of mice injected with plant extracts. This indicates that low production of willow ptarmigan chicks in microtine rodent crash years is not caused by plant estrogens in their spring food plants.