What is the observed effect of altruistic tendencies among female vampire bats? a. vampire bats who share food tend to live longer than other bats. b. vampire bats who share food tend to have fewer offspring than other bats. c. vampire bats who share food tend to die younger than other bats. d. vampire bats who share food tend to have more luck hunting fresh food.

The correct option is D.
Vampire bat feed on the blood of mammals. Vampire bats who share their food do so by regurgitating blood for their fellow vampire bat. Vampire bat prefers to share their food with relatives and kins and with those bats, who have helped them out in the past when they were hungry. Vampire bats who share their food tend to have more successful kill. 

The vampire bats feeds on the blood of mammals. So the answer to your question, What is the observed effect of altruistic tendencies among female vampire bats, would be Vampire bats who share food tend to have more luck hunting fresh food. So the answer would be letter D.

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