Sex, Treachery, and Death
Burke Museum at the University of Washington
April 26, 2012 13:30-15:20
This day we continue to examine bird specimens at the Burke Museum.
Birds have evolved in an amazing manner to increase their fitness. Their ultimate goal is to survive and reproduce so that their genes get passed on to their offspring. In order to realize this goal birds will undertake almost anything, including potentially immoral sex and treachery in the human world. But eventually they all face death.
First of all, dimorphism refers to different features between males and females due to sexual selection. For example, often times males have a distinct and brighter physical feature to attract females. Males are usually larger as well to prove their masculinity and toughness - a physical and heritable trait that is desirable for their offspring to have so that their genes could cross eternal generations. Dimorphism is a type of sexual selection, a type of evolution that puts at an advantage those individuals who are sexually fit. However, many times in exchange sexual selection is counteracted by natural selection, such as increased chances of predation, as larger bodies with distinct patterns stand out for predators to see. To mitigate the negative impact of sexual selection, many birds have adapted so that patterns start to emerge during the breeding season. Again, spatial archives at the museum allows to investigate changes over time, as mentioned in the previous journal entry. When birds with seasonal sexual selection are lined up by the time of year, the patterns of changes in their physical features become apparent.
Stronger, larger, and more distinctive males get to enjoy reproduction. The competition is fierce, partially because there is no law or morals that accompany relationships like humans do. Desirable males may get multiple breeding partners while others get none. Since it is the female that takes care of their offspring for most species, males look to breed with many as possible, while females pick and choose their partner. This characteristic apparently applies to humans as well; men like to flirt with several women whereas women pick and choose a single attractive man.
As mentioned above, females often incubate eggs until they hatch but some species, like the cuckoo. Cuckoos drop their eggs in other birds nest, basically to get free babysitting without permission. It is not quite known whether birds that were dropped a cuckoo egg in their nest, or the free babysitters, realize that there happens to be an extra egg in the nest. In many cases though, the cuckoo chick gets fed just like others for many reasons. One, birds rely on the chirping of chicks as signals to feed. In other words, that is the cue for parent birds to provide food into chicks' mouths. There are not too much variation in chirping between species, so all chirping chicks get equally fed. Secondly, birds must be strong to survive in the fierce wild. In order to realize the goal to pass on their heritage, parents may be biased to feed the larger chick, which is the cuckoo. Third, one must be overwhelmingly confident that a child in your house is not your own to throw him out forever. You could imagine how this may be when human infants get mixed up - parents may feel as if there is something not right about the baby, but you would have to be very sure to throw him out (or talk to the hospital). In addition, smaller birds like the warbler are not big enough to hold and remove the cuckoo egg between their beaks even if they do realize that it does not belong. Warblers then try to pierce through, then to realize that cuckoo eggs are very tough to strike. Cuckoos go back to their true parents nest when they grow up large enough.
To do some justice, though, there are many cases in which cuckoo birds do not get their desired outcomes. Since they are larger than other birds' eggs, they chirp with a larger volume for food, which in turn makes them more vulnerable to predators. And in some cases, the parents do carry the cuckoo bird out of the nest.
I have already mentioned this a couple of times, but since birds are not bound by ideas of morality and law, it is quite amazing to learn how they go about increasing their fitness. I am pretty sure that I am not the minority who is amazed, in fact, there are lots of dramas and telenovelas that feature sex and treachery as main themes. I believe one of the reasons why we may think that a world with rampant sex and treachery is amusing is because humans still have that instinct. Humans would probably act the same way if unregulated. And it would be interesting to see how humans would evolve in a world of birds; if some class of humans would specialize in treachery like the cuckoo.
Species list
family Cuculidae - Cuckoo bird
Dendroica petechia - Yellow warbler
Dendroica occidentalis - Hermit warbler
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