Mammals: Nature's Warm-Blooded Wonders
What are the defining characteristics of mammals?
Mammals are a diverse class of vertebrate animals that share several key traits. These include the presence of mammary glands in females, which produce milk to feed their young; a body covering of hair or fur at some stage of life for insulation; a specialised jaw structure with three middle ear bones for enhanced hearing; being warm-blooded (endothermic), allowing them to maintain a stable internal body temperature; and typically giving birth to live young, with a few exceptions like the egg-laying monotremes. They also possess specialised teeth adapted for various diets and a four-chambered heart for efficient blood circulation.
The class Mammalia is broadly divided into three main groups based on their reproductive strategies. These are:
- Monotremes: These are unique egg-laying mammals, such as the platypus and echidna.
- Marsupials: This group includes pouched mammals like kangaroos, koalas, and opossums. They give birth to relatively underdeveloped young that complete their growth and development within a pouch on the mother's body.
- Placental mammals: This is the largest and most diverse group of mammals, encompassing a vast array of species including humans, dogs, whales, and elephants. Their young are nourished inside the mother's uterus through a placenta.
Mammals are crucial for maintaining ecological balance and function in numerous ways within ecosystems. They act as:
- Predators: Controlling populations of other animals.
- Herbivores: Influencing plant communities through grazing.
- Scavengers: Recycling nutrients from dead organisms.
- Pollinators: Assisting in the reproduction of certain plant species.
- Seed dispersers: Helping to spread plant species to new areas.
- Ecosystem engineers: Physically altering their environment, which can benefit themselves and other species.
Formal surveys conducted by the Sidmouth Nature project have recorded a relatively low number of mammal species compared to the UK as a whole. Several factors likely contribute to this:
- Survey timing: Surveys are often conducted during the day, while many mammal species are nocturnal and more active at night.
- Mammal wariness: Mammals can be wary of humans and may avoid detection during surveys.
- Habitat focus: The project's surveys focus on specific sites, potentially missing species in different or less accessible habitats, such as marine areas.
- Survey methodology: The standard transect survey method used may not be ideal for detecting many mammal species, which often require specialised techniques like trapping or bat detectors.
- Landscape characteristics: The Sidmouth area's landscape, with significant housing development, reduces the amount of suitable habitat and can fragment it into small, isolated patches, making it harder to support diverse mammal populations.
Despite formal survey limitations, various mammal species have been documented in the Sid Valley through surveys, observations, and databases like iNaturalist. Some notable examples include:
- Bats: Multiple species have been recorded, including Common and Soprano Pipistrelles, Daubenton's, Greater Horseshoe, Brown Long Eared, Serotine, Whiskered, and Lesser Horseshoe bats.
- Badgers: Indicated by their activity, setts, and latrines.
- Hazel Dormice: Found in woodlands and hedgerows, dependent on specific plant species.
- Otters: Regularly seen on the River Sid, particularly in The Byes.
- Harvest Mice: Known to have a colony on Mutter's Moor.
- Shrews: Including Pygmy and Common shrews.
- Rodents: Such as wood mice, bank voles, and the non-native Grey Squirrel.
- Deer: Roe deer are noted as having a high population.
- Foxes: Seen in various habitats including town and woodland edges.
- Rabbits: Common in areas like parkland and sand dunes.
- Stoats and Weasels: Carnivores found predominantly in the upper reaches of the valley.
- American Mink: A non-native invasive species present in the valley.
Mammals inhabit a variety of environments across the Sid Valley. Important habitats include:
- Woodlands: Provide roosting and hibernation sites for bats, habitat for dormice, deer, and small mammals.
- Grasslands: Support small mammals and are influenced by grazing animals.
- Hedgerows: Act as crucial wildlife corridors and provide habitat for many species, including bats and dormice.
- Scrub: Offers important habitat for mammals, including dormice.
- Urban/Gardens/Brownfield: Exploited by wildlife like foxes, badgers, deer, rabbits, and bats, with gardens being important refuges.
- Heathland: Supports specific species like Harvest mice.
- Coastal Habitats: Used by species like rabbits on sand dunes and potentially disturbed by recreation.
- Freshwater/Riparian: Essential for species like otters and bats that forage over water.
Mammal populations in the Sid Valley, like elsewhere, face significant threats. These include:
- Habitat loss and fragmentation: Due to intensive agriculture, building development, and the loss of hedgerows, reducing the amount of suitable habitat and isolating populations.
- Changes in land management: Modern practices like intensive grassland management lead to less diverse flora and fauna, impacting the mammals that depend on them.
- Invasive non-native species: The American Mink has impacted native species like the Water Vole, and Grey Squirrels have affected Red Squirrels.
- Barriers in urban environments: Fenced gardens can reduce habitat connectivity for species like hedgehogs.
- Pesticides: Historic use of pesticides like DDT caused dramatic declines in species such as otters.
Conservation efforts in the Sid Valley focus on habitat restoration and management to benefit mammals. These include actions such as hedge replacement and laying, woodland coppicing, creating glades and rides, managing scrub, planting trees and hedges, and appropriate grazing. Creating biodiversity networks and corridors is a key strategy to link isolated habitats. Specific sites like The Knapp and The Donkey Sanctuary are managed with wildlife in mind. Individuals can contribute by managing their gardens to support wildlife, providing food and shelter, and avoiding the use of harmful chemicals. Recording and surveying mammal populations are also vital for understanding their presence and the effectiveness of conservation actions.