They experience psychological pain and depressionAnimals, too, experience a profound feeling of sadness when their play/hunt/sex partner dies. Those studying the behavior of wild and domestic animals come with an increasing number of cases proving that animals are capable of pure sorrow when they lose someone close to them. Somehow, this behavior is linked to self-conscience, thus only "brainy" animals, like mammals and some birds, consciously commit suicide.
It is hard to say if animals commit suicide. An animal will not do this because of a sudden dread, or an excessive emotion. As they cannot ... speak, it's difficult to assess if there is a true suicide.
But when a dog or a cat, following the death of their master, refuse food dying of hunger, we can conclude that this is an unwitting consequence of the pain they feel. But when the animal throws itself from a height, it's hard to believe this is a casual act or the effect of its anxiety.
This case was seen in a natural reserve in Zimbabwe: chased from their pride, the luck seemed to have encountered a pair of old hungry male lions. They cornered a warthog, but the animal escaped in the last moment in a den. One of the lions, pushed by the hunger, tried to follow it, but he got trapped in the narrow hole. His partner tried to help him, pulling him out with the paw, but when the trapped lion started roaring of pain, he stopped.
The trapped lion died asphyxiated, and the next day, his partner hardly managed to pull out his corpse. Sooner, the second lion was found dead next to the body of the other. He had refused to go hunting, and died of hunger.
Dogs are known for their strong affection feelings, and stories with suicidal dogs abound. Dogs grown together get so bound one to each other, that often do not survive to the loss of one of them. One owner had an airdale and a fox-terrier, who were always hanging together.
One day, the fox-terrier was crashed by a car and died. The owner buried it in the garden. The playful airdale changed its behavior, did not leave the tomb, refused food, and was haunting like a phantom during the night like looking for its friend. Few days later, the airdale was found dead next to the tomb of its friend.
But this attachment of the dogs is also applied to their human masters. This story occurred in Rome: the owner of Shastra, a Spanish cockerel, died. When the corpse was pulled out of the house, the dog tossed itself from the third level. It just broke one leg. It was brought to the veterinarian but once again home, the pulled out itself from the leash and threw itself again.
This time it died. Perhaps, the places in which the dog played so many times with its master could have recalled the dog such painful records that it could not resist and suicided.
This case occurred in Ostiglia (also Italy): Franz, a German shepherd dog, was laying on the railways line, near the railway station. Workers always chased away with stones the dog, but soon after the dog returned, and one day, the dog met with the Verona-Bologna train...
Franz had lost his master, condemned two weeks before to one year in jail. Since she had disappeared, the animal refused food, haunting through the city, like a suffering soul missing a beloved one.
This case occurred in the Farnese palace (Paris): a white Angora tomcat chased restlessly a pussy cat next door. But the female was indifferent to his advances, and one day the tomcat threw himself through the windows and died. The owner said because of the unshared love...
An 8-year-old girl had a cat which she surrounded with all her care and affection. The two were very bound. But the child died of a sudden condition, and everybody forgot in a such a difficult moment about the cat. When they remembered about the animal, it was gone.
Three months later, a scratch was heard at the door. It was the cat, weakened and with sad eyes. The cat refused food or caresses; it went to the girl's room, looked around, went to the open window and tossed itself: it died with the skull crashed on the pavement.
Monkeys too react in the same manner when losing a partner. Many times in Zoos, when one monkey in a pair dies, the partner refuses food, dying a few days later. Monkeys are highly intelligent, and form strong bounds with the partner.
Of course, the suicide also occurs amongst dolphins, animals considered the second after apes in what concerns intelligence level. In a Greek gulf, a pair of dolphins had been living for years. But one day the fishermen noticed that the male could not swim properly and floated with the belly up. Few days later, the male died. The female pushed the corpse, trying to keep it to the surface to "breathe".
When a storm begun, the body was taken and smashed to the rocks. Then, the female threw herself to the rocks, sharing the same faith with her partner.
As said, some birds, with a more complex behavior, can suicide, like parrots.
In a pair of pet love birds, the male got an injury that killed him in one hour. The female, witnessing the sufferance of her partner till he died, imitated all his movements, like she would have suffered the same way like him. She kept on imitating this even after her partner died, and this had a harming effect on her inner organs. Her vitality dropped, and she died soon.
But sometimes animals seem to suicide linked to depression, when serotonin ("happiness levels") drop to dangerous low levels, which is a much more common cause of suicide in humans, than longing.
A giraffe at Paris Zoo broke its head wittingly by the walls of its shelter, after a period of several days in which manifested signs of sadness and depression.
A 12-year-old lioness in an American Zoo had remained pregnant thrice, but each time she gave birth to weak cubs, which died soon. After the last pregnancy, she failed in the most severe depression. For several days she had refused food, and suddenly, she experienced a desperation crisis, starting to chew her tail as long as she reached. Than she started to chew one of her paws, and none could say the final results, if the keepers had not killed her. Post-partum depression is common also in women ...
In a English case, a farmer, renown for his brutality, bought a horse. The seller warned him not to use the whip for driving the horse. But two days later, the farmer bit violently the horse. Suddenly, the animal started running on a meadow surrounded from three parts by fences, and on a fourth side, there was a cliff dominating the sea shore. The horse galloped directly to the cliff, smashing itself on the rocks below.
In some animals, sex is pure suicidal, at least for the males. In praying mantis the female starts eating the male while still copulating, head first! And in some spiders, in which the male is a pygmy compared to female, sex is followed by its own sacrifice in the jaws of the female. In the end, males are just a piece of protein for the hungry eggs developing females. Is this a suicidal act of the male? Rather no, as he primarily has sex on his mind.
Another issue: Lemmings do not commit suicide! Each 4 years there is a cyclic demographical boom of the lemmings (small arctic rodents) followed by a desperate massive migration during which many die throwing themselves into the rivers, lakes and sea.
It has been regarded as a collective suicide, conscious or involuntary, caused by over-population. In reality, being solitary rodents by nature, when the population booms, the stronger lemmings drive the weaker and younger ones off long before the food is depleted.
The young lemmings disperse in random directions looking for vacant territory. Geographical features constrain their movements and channel them into a relatively narrow corridor and large numbers can build up leading to social friction, distress and eventually a mass panic can follow and they flee in all directions, but they do not deliberately march into the sea; this is just pure fantasy.