Thursday, February 14, 2013

Real animals love gifts

Did you remember the flowers?  Chocolate?  Large pink stuffed teddy bear?

While our current gift-giving on Valentine’s Day may have as much to do with marketing as it does relationships with our loved ones, giving gifts to prospective or actual mates is not unique to humans, and it plays an important role in biological fitness for many animals.

Biological fitness is not just about survival. Reproduction is equally key, and the males of many species, not just humans, win over their chosen one with tokens to show their affection. In some cases, it might be bribery; in others, a show of generosity; in still others, a demonstration of the ability to provide for his mate.

Which animals give the gift that keeps on giving?  Read on ---

Only some groups of animals offer gifts, though they include males with lifetime mates, males with seasonal mates, and bachelors just hoping to mate with as many ladies as possible. Providing an appropriate gift to a female takes time, which limits the time available for mating (yikes!) and thus the number of times he can mate, so it had better be worth his time.
Eurasian jay feeding mate
photo: Hankyu Kim

Long-term giving

Maintaining strong bonds between monogamous pairs is key for the fitness of both the male and female, since long-term pairs often must work together to raise young to adulthood.

Eurasian Jays, related to crows, pick out and give tasty treats to their girlfriends-- worms, rather than chocolates in this case-- and apparently try to complement rather than duplicate, what their lady love has already eaten. Sort of like dessert after a romantic dinner? These efforts strengthen the bond between the two birds, beyond any attempt to impress a potential lover.

Arctic tern bearing gifts (sushi?)
photo: ToivoToivanen
& TiinaToppila
Terns are seabirds that know how to impress the ladies, which is key when females judge their potential mates on the size and number of fish they are presented with. The biggest and most lavish gift givers among terns get to join their chosen female in an acrobatic celebratory flight before heading off to choose a nesting site. The male doesn't then run off - he continues to feed and support the female while she is laying eggs, which both encourages her to mate with him and to lay more and stronger eggs.

Kingfishers are equally rewarded with female attention when they offer the right fish at the right size. If she refuses him, or takes too long deciding, he is known to just eat his fish gift right in front of her. Fitness fail?

In North America, Northern cardinals, chickadees, and warblers do the same thing, offering seeds or other foods to their mates, both before and after mating occurs. Such continued generosity through the breeding season actually increases the male's fitness (in the form of higher reproductive success by keeping her fat and healthy).

Short-term giving

Gift-giving is part of courtship even among species that are polygynous (>1 female), as males hope to attract and mate with multiple females. Among polygynous species, male birds are again among the champion gift givers, offering the latest in food, flowers, and forest beauty to females. Male bowerbirds in Australia and New Guinea build elaborate structures called bowers (they are not nests!), which they decorate with small, often shiny objects that attract female attention.

His bower and associated goodies show the females how fit he must be to have been able to gather and compose both the structure and the decor.

Male satin bowerbird offering the latest in blue trinkets

Why does he do all this? Well, to MATE, basically. More mating = More offspring = Higher fitness. And that is what they are all aiming for!

Prepare to be impressed by the dedication of the Vogelkop bowerbird of New Guinea, shown in this BBC video. He offers not only flowers (pink!) but also fruits, nuts, leaves, and astonishing gardening and architectural skills. Perhaps his impressive gifts make up for his relatively plain feathers-- he has great attitude, optimism, and practicality!

Male bowerbirds provide no parental care and give nothing to females except sperm, so a larger stronger, more clever male that can find, display and defend a swanky bower appears to be just the guy most females are looking for. While the females themselves don't gain direct benefits from choosing such a strong capable male, by choosing a fellow with good genes and passing them on to her young, she improves their chances of survival and breeding. This makes good use of her nesting efforts and improves her own fitness in the process.

It sounds reasonable, but is this true? One scientific study found that bower decor attracts females to the site, but, for actual mating, a male's body size matters - more than his architectural masterpiece. However, another study of the same bowerbird species showed that "good" bower decor both attracts females and improves mating success.

Birds may be more frequent gift-givers, but, like us, our closest relatives also show their interest and appreciation through gifts, with these two cases definitely not strengthening long-term pair bonds.

Male chimpanzees will give treasured meat to unrelated females, at times seemingly in return for sex. Not too subtle. But sometimes mating doesn't necessarily follow, leading the scientists studying this behavior to suggest that the males are in this gig for the long term. As one lead scientist put it, "What's amazing is that if a male shares with a particular female, he doubles the number of times he copulates with her, which is likely to increase the probability of fertilising that female." The protein in the meat may be highly valued by females, who hunt less and thus have less access to meat.
Sex for stress relief and bonding - bonobos

Similarly, bonobos (a.k.a. pygmy chimpanzees) are renowned for their active sex lives, and male bonobos sometimes offer fruit to females with whom they want to mate. It doesn't even seem necessary (this page looks scientific, but skim down to see what I mean - "...anything, not just food, that arouses the interest of more than one bonobo at a time tends to result in sexual contact..."). Apparently, the pre-food sex is a stress-reduction technique, not a bargaining chip!

Really short-term giving

On the other end of the size and mating spectrum, certain male spiders have learned to present gifts in the form of dead insects, to prospective mates. This may be a means of self-preservation in the face of their polyandrous (multiple male mates) and indiscriminately predatory female companions, which are known to eat their suitors. Wrapping the insect gift in a web of silk may occupy the female's attention, further improving the males’ odds of escaping the mating process alive. (The males of at least one spider species give females just a wad of empty silk or silk wrapped around some non-food item—ladies beware).

So on this Valentine's Day, enjoy any giving and receiving of gifts, happy with the thought that your future survival doesn't necessarily depend on it!

For more information:

Have a look here and here for more on some of the world's most romantic animals, including gift-givers, dancers, and massage artists.

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