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mangrove challenge

Nest (high-rise on the supralittoral zone)

Photo of a mud mound nest
Termitarium-like mud mound nest in Marine Couch grassland at low tide.
Photo: Steve Van Dyck, QM

Photo of nest flooded
At high tide, the lower openings and tunnels of the nest have been flooded.
Photo: Steve Van Dyck, QM

The House Mouse makes nests and lives in groups, but not in the grand style of the Water Mouse. No other small mouse anywhere in the world builds and lives in the immense mud mound nests of the Water Mouse. They build nests in the supralittoral zone, in the area above high water mark behind the mangroves. Their nests show the Water Mouse's high degree of specialisation to living in mangroves because it has found a way of maximising the areas where it can rest and forage.

The supralittoral zone acts as a buffer between marine and land communities. It floods periodically at very high or spring tides, and often has saltpans, so only tough grasses such as Marine Couch and some succulents can grow there. In other swampy supralittoral zones sedges and rushes grow in dense bands. The Water Mouse uses some parts of all of these plants cemented with mud to build its nests.

Not all Water Mouse nests are interesting 60 cm termitarium-like mounds of mud, peat, straw and crab carapaces. Sometimes they are no more than tunnels in the banks behind the mangroves, in the roots of fallen mangroves and other trees, or in bulldozed soil. Even in these places, the Water Mouse maintains the nest by doing mud work or plastering to repair water damage. For this reason, the nests often become larger over time.

A Water Mouse and its social group rest together in the nest, and sometimes mate, during high tides and by day. The group might consist of up to eight mice - one male, one female, several juveniles and babies. The nest usually has several tunnels and openings, with nesting chambers at the top lined with leaves. Nests are an important part of Water Mouse territories, and small spats between mice from different social groups are often observed near them.

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