Sibling Rivalry

Question 1

What is sibling rivalry?

Answer 1

A form of competition between siblings for food, resources, or parental attention.

It is common throughout the animal kingdom.

Question 2

The most extreme form of sibling rivalry is…

Answer 2

Siblicide.

Question 3

Facultative Siblicide

Answer 3

Might or might not happen, depends on the environmental conditions.
More species have facultative siblicide than obligate.

Question 4

Obligate Siblicide

Answer 4

Almost always the case that one offspring will kill another offspring, usually the largest killing the smallest.

Question 5

Why does siblicide exist?

Answer 5

1) A way to deal with overproduction (when parents produce more than they can raise, they may promote siblicide)
2) A consequence of asynchronous birth (young are born at different times, and parents start incubation at different times. the firstborn gets a head-start and monopolizes resources.)

Question 6

Sibling rivalry – Spotted Hyenas

Answer 6

Usually born as twins in a burrow far away from the clan’s den. They are born well developed, with open eyes and strong teeth. These teeth are used in sibling conflict. When newborns are of the same sex, there is even more aggression, and the second cub to be born will likely die.

Question 7

Blue Herons vs. Great Egrets

Answer 7

Siblicide is rare in blue herons (who provide young with large fish that is impossible to monopolize). Siblicide is common in great white egrets (who provide young with small clumps of fish that can be easily monopolized), and almost certain in four egg clutches – parents do not interfere with this behaviour.

Cross fostering experiment found that great egrets continued to fight and show siblicide when they could not monopolize fish brought by blue herons, while blue heron chicks showed lots of aggression and siblicide was common.

Question 8

Sibling rivalry – Pigs

Answer 8

Pigs give birth to more young than they can raise (variable amount of young, and variable amount of nipples). Pigs are born with canine teeth that may have evolved for sibling conflict.

Experiment found that pigs who had not had their teeth clipped gained more weight than their clipped littermates.

Question 9

Parental responses to too many kids

Answer 9

• Neglect weak offspring
• Feed food that can be monopolized
• Direct brood reduction
• Control synchrony of incubation
• Make first eggs bigger than the last
• Put more androgens in earlier eggs
• Promote or ignore sibling rivalry / siblicide