Lutra 60(2)_Mulder & van Maanen_2017

A case of winter reproduction in the stoat (Mustela erminea). An effect of artificial light?

Most of the northern hemisphere’s mustelid species (18 out of 27), including the stoat (Mustela erminea), exhibit delayed implantation (Mead 1989) in which after mating and successful fertilisation in spring or summer, the development of the embryo stops at the blastocyst stage after approximately two weeks. The blastocyst remains free-floating in the uterus until implantation, which occurs nine to ten months later (King & Powell 2007). The moment of implantation is strictly governed by the increasing ratio of natural light-to-dark hours in spring, which is hormonally controlled by the Leukemia Inhibitory Factor (LIF), in a complex feedback process. Ambient temperature changes have not been shown to affect the cycle. After implantation the embryo develops to the birth stage in 28 days. Delayed implantation in stoats is fixed and shows no apparent variation (King & Powell 2007). In north western Europe, the birth of stoats occurs between mid-April and mid-May. This means that the implantation of the blastocysts occurs around the first of April. There are no records in the literature
of births occurring at other times of the year.

At the end of June and the beginning of July female stoats can be seen travelling around with their almost full grown young in tow, which soon after become independent (Mulder 1990, King & Powell 2007). On 26 January 2017 several photographs of a stoat were taken by Gert Stegeman in the Netherlands (published on The animal was crossing the ice over a ditch to the south of the town of Steenwijk (52.7638 N, 6.1184 E). The stoat was carrying a light-coloured, shorthaired, juvenile mammal.....