Certain species of rats are highly adapted to subterranean life, constructing elaborate networks of tunnels beneath the ground. This successful survival strategy allows these rodents to thrive in diverse environments, especially those altered by human activity. The underground habitat provides consistent shelter and access to resources. Understanding the structure and purpose of these burrows is key to grasping how these common urban and rural inhabitants sustain their populations.
Which Rat Species Are the Primary Burrowers
The capacity for extensive burrowing primarily distinguishes the Norway rat, Rattus norvegicus, from the other major commensal species, the roof rat, Rattus rattus. Norway rats are often called brown rats or sewer rats due to their preference for ground-level and subterranean habitats. Their physical characteristics reflect this fossorial, or digging, lifestyle.
Norway rats have a stockier, heavier build, weighing between 12 and 17 ounces, with a blunt snout and a tail that is shorter than their head and body combined. They are powerful diggers and also excellent swimmers, often inhabiting areas like sewers, riverbanks, and basements where they can easily access the ground layer.
The roof rat is an agile climber, possessing a slender body, a pointed snout, and a tail that is longer than its head and body combined, which aids in balance. These rodents are primarily arboreal, preferring to nest in elevated locations like attics, trees, and utility lines. While they may use existing ground-level cover for shelter, they rarely, if ever, excavate burrows.
The Architecture of a Rat Burrow
The subterranean home built by a Norway rat is a complex, multi-functional system of tunnels and chambers. These rodents display a strong preference for constructing burrows in loose soil, especially near solid structures like building foundations, under concrete slabs, or along riverbanks and dense vegetation. The initial entrance to the burrow system is typically a clean-cut hole, often 2 to 4 inches in diameter, which leads into an expanding network.
The tunnels branch out and descend, sometimes reaching depths of several feet, that can house a large, hierarchical colony. Within this network, specific chambers are excavated for different functions. The nesting chamber is a particularly important area, often lined with soft materials like shredded paper, fabric, or insulation, providing a secure place for breeding and raising young.
The burrow system includes secondary, concealed exits known as “bolt holes.” These smaller, often camouflaged openings are kept just below the surface and serve as quick escape routes when a threat is perceived near the main entrance.
Why Rats Prefer Underground Habitats
Living below ground offers substantial security and survival advantages. Burrows provide highly effective protection from a variety of above-ground predators, such as cats, birds of prey, and humans. The enclosed tunnels and chambers act as a safe haven, allowing the rats to retreat instantly when confronted by a sudden noise or perceived intruder.
The subterranean environment also provides a stable climate. The earth acts as an insulator, maintaining a consistent temperature that shields the rats from both scorching summer heat and freezing winter cold. This thermal regulation is especially beneficial for the vulnerable young, contributing to higher reproductive success.
Furthermore, the burrow serves as a secure location for key biological activities, including nesting, raising litters, and food storage. The protection offered by the underground structure allows females to breed and nurse their young with minimal disturbance. The tunnels are also used to stash gathered food.