Thinking About Galapagos (6): Animal Mating, Marriage, and Parenting

                                               Pitt Point with the Cormorant in the Bay

Pitt Point (Punta Pitt) is the only place in Galapagos where one can see all three species of boobies mating and nesting--Blue-footed, Red-footed, and Nazca Boobies.  The Nazca Booby is an endemic species--that is, the species is found only in Galapagos and no where else in the world.  The Blue-footed Booby and the Red-footed Booby are endemic subspecies--that is, they are subspecies found only in Galapagos, but closely related members of the same species are found elsewhere in the world.

As indicated in some previous posts, Thomas Aquinas and John Locke appealed to the monogamous mating and biparental care shown by many birds as manifesting the natural law of marriage and parental care.  We might wonder whether the Galapagos boobies show this.  (This issue was part of my paper--"The Darwinian Science of Thomistic Natural Law"--presented on March 4 at the conference on natural law at Cambridge University.)

Here is a video of the mating dance of the blue-footed boobies:

After hiking up the steep and rugged cliff to the top of Pitt Point, we saw many nests.  Then we saw the famous courtship ritual of the blue-footed boobies.  A female landed and displayed towards a male.  They advanced toward each other.  Then a second male landed near the female, so that now she had to choose between the two males.  This is what Darwin called "sexual selection" in The Descent of Man: the female chooses the most attractive males, or the males compete among themselves for the female.  Unlike natural selection, sexual selection introduces an element of mental choice into evolution, in that the reproductive fitness of the male depends on his being chosen as attractive.

The blue-footed boobies have been studied intensely not only in the Galapagos but also elsewhere in the eastern Pacific tropics.  Over 35 years of study has been done by Hugh Drummond, a professor at the National Autonomous University of Mexico, who has returned every year to study the blue-footed boobies on Isla Isabel, which has been called the Mexican Galapagos (Angier 2017, Vance 2015).  Isla Isabel is a tiny island 15 miles off the Pacific coast of Mexico and southeast of the Baja Peninsula.  Isla Isabel is a volcanic island that is about one-half mile wide and three-fourths of a mile long.  So Drummond's 35-year-long study of the blue-footed boobies on this tiny island is comparable to the 40-year-long study of the finches on Daphne Major by Peter and Rosemary Grant.  In both cases, these scientists have studied the social life history of a unique community of unique individuals on one small island, which illustrates the contingency of biological historicity and animal personalities.

Experimental research has shown that a female blue-footed booby is prudent to choose males with the bluest feet, because blueness is an "honest signal" of being well-feed and healthy.  When a male is deprived of food or infected with a pathogen, the color is drained from his feet, because he's not getting the natural carotenoid pigments from his diet, or the carotenoids are being channeled into his immune system. So if he is feeding well and healthy, the female should choose him for mating, because he might pass on some of his innate hunting skills or his robust immune system to her chicks, and he is more likely to provide well for them as they grow (Verlando et al. 2005, 2006; Torres and Verlando 2007). 

Does it work the other way?  Does the male choose the more attractive female?  Since the male is investing so much in the care of the offspring, we might expect that he would be choosy about his partner.  Indeed, experiments where the female's feet are painted to show a pale color show that she then receives less attention from her partner and from other males.  So it seems the males want to see in their partners the signs of health and attractiveness (Torres and Velando 2005).  Here then we see mutual sexual selection.

Blue-footed boobies show intense biparental care.  They can live for 20 years or more.  They start reproducing at the age of 3-5 years.  They return almost every year to the place of their birth to mate and rear their offspring.  Early in the seven-month breeding season, males establish territories.  Females pair with males on their territories.  Females are larger than the males.  Females have a larger eye pupil.  And females honk harshly during courtship displays, while males whistle gently.  They perform their courtship displays and copulate for a few days or several weeks until the female lays one to three eggs at intervals of about 4 days.  Both parents share parental care during 41-49 days of incubation and three to four months of chick rearing until fledgling.  Females provide more food to the young, while males invest more in territory defense. During any one breeding season, most blue-footed boobies breed only once, although a few will attempt to breed twice if the first clutch has been lost.

Blue-footed booby siblings are in competition.  Like Cain killing Abel, the older chick sometimes kills the younger one.  If the younger becomes submissive to the older, the younger one can usually survive, although the older one will receive more food from the parents.

Although blue-footed boobies are socially monogamous, in that a male-female pair jointly care for their offspring during a breeding season, both males and females occasionally engage in extra-pair copulations, and there is a high divorce rate, in that after a pair has mated for one breeding season, about 50% of the pairs will break up in the next breeding season, and the individuals will seek a new mate.

So was Aquinas right in arguing that the monogamous mating of birds who jointly care for their offspring shows the natural law of monogamy and parental care for human beings?  If he was looking for life-long sexual monogamy without divorce, then the blue-footed boobies and most other birds will not satisfy his standard.

Nevertheless, there is some evidence that the blue-footed boobies provide at least partial confirmation for Aquinas's argument in that they show the increased reproductive success that comes from enduring pair bonding.  Drummond and his colleagues have analyzed the data on the annual reproduction of 752 breeders over 24 years on Isla Isabel to show that those pairs that have stayed together for four years or more have increased reproductive success (Sanchez-Macouzet, Rodriguez, and Drummond 2014).  Those pairs that stay together establish their clutches early in the breeding season, more of their eggs hatch, and they produce 35% more fledglings than do newly bonded pairs.

They explain this by arguing that pairs that stay together over multiple breeding seasons gain a familiarity with their mates that promotes better coordination and cooperation in their reproduction and parental care of their offspring.  So Aquinas was right about this.

Now, we might object that extra-pair copulation will reduce the fitness of those in enduring pairs.  But of course extra-pair copulations produce no losses to female fitness, because the females can generally be sure of their maternity.  And while males cannot be so sure of their paternity, the probability of extra-pair paternity is small enough that the cost to male fitness is trivial in comparison with the great increase in producing fledglings.

So if enduring pair bonding really does increase the reproductive fitness of blue-footed boobies, why do they show such a high divorce rate--about 50% per year?  Drummond and his colleagues suggest various possible explanations for this.  It is sometimes hard for pair members to synchronize their arrivals at the breeding site, and the individual that arrives earlier might not be willing to wait for a mate that might arrive too late or not at all.  There might be some advantage in having genetic diversity in offspring.  Pairing with a new high-quality mate might be more beneficial than staying with a low-quality mate.  A third party might coercively break up a pair bond.  The factors that influence the mating and pair-bonding of birds can have some of the same complexity as arises among human beings.

But is it reasonable to think that the mating and parenting behavior of birds and other animals can tell us anything about human mating and parenting?  Robyn Hudson, an animal behavior researcher who works with Drummond, has remarked: "You're kidding yourself if you think boobies can predict human behavior.  But you're kidding yourself if you're sure they don't."  Drummond has said that although boobies don't reason the way human beings do, there is some connection between the experience of the boobies and human experience.  "The booby brain is a sort of computational organ," Drummond has said.  "I would put my money on them having rudimentary emotional experience and rudimentary thoughts.  But not moral thoughts" (Vance 2015).

Aquinas said something similar.  Nonhuman animals do not have the uniquely human capacities for rational deliberation and moral judgment, but animals do have rudimentary capacities for thinking and emotion.  Birds and other intelligent animals consciously apprehend the objects of their desires, gather and assess information in their environment relevant to their desires, and then act according to their "estimative" judgment of how best to satisfy their desires.  In doing this, they learn to apprehend physical things and other animals as pleasurable or painful, useful or harmful, friendly or hostile.  They act voluntarily in that they initiate acts as guided by some knowledge of their goals.  They remember the past and anticipate the future.  As social animals, they judge the intentions of other animals and communicate with them to act for common ends.  They display and recognize social emotions such as love, hate, and anger.  They learn from experience, and they transmit what they learn to others.  Thus, Aquinas observed, animal lives show "a certain likeness of moral good" (similitudo boni moralis).

As we waited at the top of Pitt Point to see which of the two males the female would choose, we were surprised when a third male landed nearby, and two of the males paired off together.  Then the female and the third male copulated.  We laughed and joked about the complexity of booby sexuality.  I do not know of any research that confirms that blue-footed boobies can display homosexual propensities.  But this would not surprise me, because at least as many as 132 bird species show homosexuality, as indicated in a previous post.

That evening, after we had returned to our cabins on the Cormorant, we were surprised by an announcement that one of the couples in our group--Melanie and Hayo (a German couple living in Switzerland)--were to be married that evening on the top deck of the boat by the Captain.  The crew appeared in their dress white uniforms.  The boat was anchored not far from Kicker Rock. 

Melanie and Hayo had lived together for eight years, after meeting in New York City.  Like the other people on the Cormorant, they are successful professional people.  Melanie is a physician who has become a high executive in big pharmaceutical firms.  Hayo is a Swiss banker.  Having become wealthy from global commerce, they travel extensively around the world for business and pleasure.  They take pleasure in learning about the diverse cultural lives of people around the world and in learning about the evolutionary history of the world, and even of the Earth's position in the universe.  We have talked earlier in one of our dinner conversations about the possibility of finding intelligent life on other planets revolving around distant stars.  All of these people are confident that this evolution of the Earth and of the Universe can be explained by Darwinian science without a creationist religion.

Melanie and Hayo have friends scattered all around the world.  As they thought about marrying, they were concerned that it would be impossible to gather these friends in one spot at one time for a wedding ceremony.  So they decided that they would travel through South America and the Galapagos in the month of January, and if they found some new friends in the circumstances that felt right, they would invite them to witness their wedding.  They decided that the five people they had met on the Cormorant were right for this, and the Galapagos was the right place for this.

 

 

The Wedding

That evening, after the celebration of the wedding, we gathered for dinner.  Melanie said that she thanked Charles Darwin for bringing this group of people thinking about evolution together for their wedding.


REFERENCES

Angier, Natalie. 2017. "On Galapagos, Revealing the Blue-Footed Booby's True Colors." New York Times. March 6.

Sanchez-Macouzet, Oscar, Cristina Rodriguez, and Hugh Drummond. 2014. "Better Stay Together: Pair Bond Duration Increases Individual Fitness Independent of Age-related Variation." Proceedings of the Royal Society B 281: 1-7.

Torres, Roxana, and Alberto Velando. 2010. "Color in a Long-Lived Tropical Seabird: Sexual Selection in a Life-History Context." In Regina Macedo, ed., Advances in the Study of Behavior. Vol. 42: 155-188.

Vance, Erik. 2015. "Hugh and the Boobies." Hakai Magazine. April 22.

Velando, Alberto, et al. 2005. "Male Coloration and Chick Condition in Blue-Footed Booby: A Cross-Fostering Experiment." Behavioral Ecology and Sociobiology 58: 175-180.

Velando, Alberto, et al. 2006. "Pigment-Based Skin Colour in the Blue-Footed Booby: An Honest Signal of Current Condition Used by Females to Adjust Reproductive Investment." Oecologia 149: 535-542.