What causes street rats to die? - briefly
Urban rats die mainly from infectious diseases, toxic exposure, predation, vehicle collisions, and severe malnutrition. Secondary contributors include extreme weather, inadequate shelter, and intraspecific aggression.
What causes street rats to die? - in detail
Urban rodents face a range of lethal pressures that act individually or together to reduce their populations. The most significant factors include:
- Pathogenic infections – bacterial diseases such as leptospirosis, salmonellosis, and streptococcal infections can cause rapid systemic failure. Viral agents like hantavirus and rat coronaviruses produce severe respiratory and renal damage. Parasites (mites, fleas, helminths) weaken immune defenses, making secondary infections more likely.
- Chemical toxins – anticoagulant rodenticides (warfarin, bromadiolone) interfere with blood clotting, leading to internal hemorrhage after ingestion. Organophosphates and carbamates disrupt nervous function, causing paralysis and respiratory arrest. Heavy metals (lead, mercury) accumulate in tissues, impairing organ function.
- Predation – feral cats, hawks, owls, and snakes capture rats opportunistically, especially juveniles. Predators exert selective pressure that removes weaker individuals and can trigger population-level declines during breeding seasons.
- Vehicle collisions – urban traffic presents a constant hazard. High-speed impacts crush thoracic structures, while lower-speed runs cause traumatic brain injury and internal organ rupture.
- Nutritional deficits – scarcity of reliable food sources leads to chronic malnutrition. Protein deficiency reduces muscle mass and immune competence, while dehydration compromises renal clearance and electrolyte balance.
- Extreme environmental conditions – heat waves cause hyperthermia, dehydration, and heatstroke; severe cold induces hypothermia and frostbite. Rapid temperature fluctuations stress metabolic regulation, increasing mortality risk.
- Intraspecific aggression – territorial disputes result in bite wounds, blood loss, and secondary infection. Dominant individuals may restrict access to shelter and food, indirectly causing subordinate deaths.
- Urban infrastructure hazards – exposure to sewage, contaminated water, and sharp debris can cause internal injuries or introduce toxic pathogens. Construction sites often disrupt burrow networks, forcing rats into exposed areas.
Each cause can act alone or synergistically. For example, a rat weakened by parasitic load may be more susceptible to anticoagulant poisoning, while a traffic injury can expose the animal to bacterial contamination, accelerating septic decline. Understanding the interplay of these mortality agents informs effective pest management and public‑health strategies.