Animals become more aggressive in the heat, just like people

Intense heat can increase irritability and aggressive behavior through several mechanisms: thermal stress reduces tolerance and increases impulsivity; heat causes decreased sleep, which leads to fatigue, which in turn reduces reaction control; water and food supplies decrease, and competition between animals of the same species increases.

Thermal stress

To maintain body temperature, the body activates systems such as the hypothalamic-pituitary-adrenal axis , increasing stress mediators, including cortisol. This can make the animal more reactive to stimuli: thermal stress can affect neuroendocrine systems and neurotransmitters involved in mood, fear, and aggression.

Physical discomfort and self-control

Labored breathing, increased body temperature, dehydration, and fatigue can all contribute to a feeling of discomfort. An ill animal may have a lower tolerance threshold and react poorly to approach or contact. Excessive heat can temporarily impair certain brain functions, especially those involved in assessing situations and inhibiting impulsive responses. In practice, it may become easier to react rather than "stop and evaluate."

Effects on the brain

Excessive heat can affect the brains of animals, especially when body temperature exceeds the body's ability to maintain it within normal limits. High body temperatures alter the functioning of nerve cell membranes, and intense heat can alter brain chemical systems involved in attention, motivation, fear, and impulse control. This can contribute to increased irritability or reactivity.

Finally, the body tries to dissipate heat by increasing blood flow to the skin. However, if heat stress becomes significant, perfusion and oxygen supply to the brain can be affected.

Less sleep and rest

Heat makes it harder to rest, and fatigue can reduce reaction control. To fall asleep, body temperature must normally decrease. When the environment is very hot, this heat loss becomes more difficult, and the animal may take longer to fall asleep and experience more fragmented sleep. Intense heat can increase awakenings and reduce sleep continuity. The animal may therefore sleep for the same apparent number of hours, but achieve less effective rest . Finally, during sleep, the brain performs important recovery processes: its deprivation can make it more difficult to control fear, frustration, and aggressive impulses.

Dehydration

When water is lacking, the body activates hormonal systems to conserve it, such as ADH (vasopressin) and the renin-angiotensin-aldosterone system. This signals the body that it is experiencing a significant physiological need. Water loss can alter cell volume and electrolyte balance, affecting the transmission of nerve impulses. Significant dehydration can cause irritability, difficulty paying attention, and behavioral changes.

• Scarcer resources

• During very hot periods, water, food or cool areas can be reduced, increasing competition between animals, all engaged in a tiring "hunt for food".“. If food or water is abundant, many individuals can access it without conflict. If instead they are limited, Individuals find themselves in direct competition. When water is scarce, for example, a water source becomes extremely important because it can determine survival. Defending it can therefore become advantageous, if not essential. Prolonged scarcity can cause physiological and psychological stress: this can reduce the threshold at which the animal reacts to a threat or competitor.
• Changing habits
• To avoid the hottest hours, many animals become more active at night, at dawn or at duskThis can alter encounters between individuals and increase overlap between animals that would normally frequent different places or times. Heat and drought can make some areas less suitable for survival. Animals may then move towards cooler and shaded areas, concentrating in smaller spaces: this increases the density of individuals and therefore also the opportunities for conflict.
• The increase in aggression following great heat is not common to all animals, and in fact there are very significant differences. Warm-blooded animals (Mammals and birds maintain a relatively stable body temperature by producing heat internally. However, extreme heat waves require a huge expenditure of energy, which reduces tolerance levels and mental clarity. Cold-blooded animals (Reptiles, amphibians, fish, and insects are the most affected. Environmental heat directly increases their metabolism, requiring more calories. This forces them to compete much more aggressively for food and territory. Specific studies on tropical fish (such as the Julidochromis ), freshwater fish, alpine ants, and salamanders show significant spikes in violence as temperatures rise. In the United States a research di Kailey E. Bissell and Kristen K. Cecala, published in 2019 on Freshwater Science, and concerns three species of torrent salamanders of the genus Desmognathus In the eastern United States, it has been shown that they become up to four times more quarrelsome if temperatures rise by 5-10 degrees above normal. A common scenario with the climate crisis. 

Read also: 

• How to protect dogs and cats from the heat
• Summer diseases in dogs and cats