Harvest mice nesting

1 DO HARVEST MICE BUILD MORE THAN ONE NEST?

Yes. Harvest mice build two types of nest: non-breeding (used year-round as temporary shelters) and breeding (used in the summer for raising young). Both males and females construct the non-breeding nests, which are roughly 4cm in diameter and often low to the ground, but only the female builds a breeding nest, 10 days before giving birth. This is slightly larger at 6–10cm in diameter and is usually sited at least 30cm above the ground.

2 HOW IS THE SPHERE-LIKE SHAPE CREATED?

Harvest mice weave their spherical nests from living plants, such as grasses and reeds, which provide a strong supporting structure. A mouse starts by splitting the wide blades into strips (along the veins to retain strength), then weaves them into a loose ball using its paws and mouth. Next, it works from the inside, adding more strips of grass and pulling the framework tightly together. The spherical shape (and lack of an obvious entrance) provides a secure place for a mother to raise her young, and also helps to maintain a suitable nest temperature.

3 WHY NEST HIGH UP IN THE GRASS?

Harvest mice spend most of their time feeding in the ‘stalk zone’ (at least 30cm above ground in grasses; 1m in reeds), so it makes sense to nest in the same area. Nesting off the ground also affords some protection from predators, but the nest must be supported by and secured to the surrounding vegetation. This means harvest mice are unable to breed in areas where the grass or reeds are too short, too thin or too weak. The loss of habitat that fulfils the species’ nesting needs is thought to be one of the main causes of its decline.