Home (or Nest) Security Assured

Since we’re on the topic of nesting, I thought I’d bring up another species which has some seriously intense nesting endeavors. Rhinoceros Hornbills are large birds which live in the tropics, and mate for life. This is most likely due to the fact that the females must invest a HUGE amount of trust in her chosen mate, as he will be the sole provider of food for both her and the chicks while they sit in their tree-hollow nest.

Male Rhinoceros Hornbill outside their chosen nest cavity.

And in case you think it’s just a matter of incubating eggs, think again. The females REALLY depend on males, because she is literally sealed inside of it. Once the birds find a mate, they begin to create a nest inside of tree hollows. Once the nest is created, both the male and female begin to form a wall across the opening out of mud, bits of food, and feces. They leave only a narrow slit in the middle, through which the males will pass food to the incubating mother. Who will remain sitting on that egg for 50 days until it hatches, then an additional 90 days thereafter before breaking out of the nest.

You can see the females beak sticking out of the opening, which will most likely be sealed further.

The chicks then re-seal the entrance themselves (with a little help from the parents) and again the process of passing food through a narrow slit begins until the chick is ready to emerge on its own. At that point it breaks free with some help from its parents.

Juvenile hornbill poking its head out of the nesting cavity.

There is absolutely no question as to the security from predators the chick and mother gain from this time intensive nesting behavior. The nest is kept clean through all this by continual removal of uneaten food and feces (when they’re not being used to re-create the nest seal). This nesting behavior must have, looking back, been able to evolve due to the presence of total monogamy in mating pairs, as no one male would be able to support 2 completely and utterly dependant families.

While incredibly interesting it is also a somewhat frightening concept to any woman when you think about being sealed into a small, dark enclosure with your child for months on end. Though you cannot doubt your safety is assured, as long as your husband comes back…

Aww... she trusts him so much!!!

 Picture Credit

http://www.besgroup.org/2007/02/21/hornbills-at-changi-looking-for-a-nesting-cavity/

http://fullcirclepix.com/blog/?p=856

http://www.besgroup.org/2009/05/

http://twearth.com/species/rhinoceros-hornbill

Taking the Term "Homemaker" to a Whole New Level

While most courtship displays involved males showing off their vocal skills, bright plumage, or impressive dance moves sometimes females can appreciate skill of another kind. Weaver birds are passerines, and while like most passerine species their mating calls are usually elaborate, long, and complex they pale in comparison to their real mating displays. Which are nests.

I've seen houses with less structural stability than this.

There are a number of different species of weaver birds, but in all of them the males construct incredibly elaborate hanging nests from blades of grass or palm leaves they find around them. The process takes a lot of time, and more importantly a lot of skill. Almost all the openings are at the bottom to dissuade predators from invading the nest. Females come and inspect the nests, and those males with the best construction and handiwork get a mate to help fill it once it's complete. In some species the females will even help the males complete the nests construction if the males have shown a solid enough base work and progress.

I want you to take a second to appreciate the amount of skill and practice required of these males to make these phenomenal nests. They have to tie knots, the kind we humans use daily, and from there they must hang and build upon a single blade of grass. Let me repeat this, it ties knots with only a beak and its feet. It takes years of practice for young males to really master a nest, and some never do. Then there is the absolutely heart breaking moment where a male realizes his nest simply isn't up to snuff, and has to simply CUT IT LOOSE and start again. Other species build huge communal nests which can last up to 100 years as every male in the colony will help construct and maintain it, as well as the little rooms within it. Because yes, they divide them into rooms for nesting, sleeping, and eating.

Social Weaver Bird nest. It's as large as it looks.

Clearly, I am quite impressed with this amazing behavior.  It's a little mind boggling how this complex, intricate skill would have evolved over time (though it seems to clearly be driven by nest predation as the goal is to create a safe nest for offspring).


So I will leave you with this video of David Attenburough narrating the process of a skilled male and a very novice male (who by the end you just want to hug...) create nests. Enjoy and be amazed.

Pictures:
http://www.telegraph.co.uk/earth/earthpicturegalleries/8655331/Animal-pictures-of-the-week-22-July-2011.html?image=33

http://journals.worldnomads.com/willlou/photo/1245/24442/Namibia/A-socialable-Weaver-Bird-nest#axzz32M8zPZdZ

Father of the Year, Surprisingly.

Mating behaviors in birds quite frequently involved female-mate choice, in which males have elaborate ornamentations, dances, or structures they build and display towards females in order to secure a mating. Bright feathers, long tails, colored feet, and more visually stunning traits are frequently used by males. So I was personally a little intrigued when I heard about Emu mating dances, as Emu’s are really quite dull looking birds.

After clearing the tears from my eyes for laughing so hard at the first video clip I found of this, I must say it is indeed a very interesting mating dance they perform. Not having wings built for flight the dance is mostly consistent of neck swivels, strutting, and occasionally dropping their necks down to the ground and sort of walking a few steps like that.

Here is a video, start it at 0:37 sec for the best display of the dance by both birds and forgive the hokey country music. This was the best, most detailed video of both birds participating I could find.

Besides the highly entertaining visual of watching an essentially wingless bird attempt to jump about while keeping it’s balance, the matching behavior of Emus is actually quite interesting. For about a 2 month span in the winter males will begin the display to the females who are actually slightly larger in size. If she’s impressed with the dance, the male then has mating opportunities for the next 5 months or so until the eggs are laid, if she doesn’t like it she’ll become highly aggressive and chase him off. Female Emus who do choose a mate will actually guard that male against other females, as the species is promiscuous. Quite the role reversal from what we normally observe in birds. Even more interesting is that the eggs are incubated by the male, the mother generally leaving and only occasionally returning to check in on the brood and incubating male. After hatching, the males continue to rear the chicks and guard them, quite aggressively, from other birds (even the mother of the chicks if he’s really protective).

Males taking charge of chick-rearing is not nearly as common in birds, where the majority of species involve either bi-parental care or solitary females rearing the offspring for the chicks to survive. Infanticide by males is also fairly common in birds, yet here we see males building nests, incubating eggs entirely on their own, and then protecting and feeding chicks for 7 months after hatching. For a rather dull looking bird who to be quite honest looks like he’s having an epileptic fit while trying to impress females, they actually display a rare level of male-parental care when it comes to offspring.

Feathered Stepfathers?

           Many bird species will produce 2 broods of offspring within a season. In some species, this increases the opportunities for males to breed and produce offspring, win for the males. However, the females don’t always stay with the same male they produced the first brood with. For instance, if the first brood fails to hatch at all due to neglect or simply bad luck. The guys get blamed, and the ladies will move on to find a mate whose offspring will actually hatch and eventually fledge.

            Infanticide is a possibility in situations like these, where if a new male takes over a territory or wants to induce the female to brood again sooner (with him, obviously) the males may damage the eggs beyond repair, or simply neglect the current brood so they will fail. Some researches have, as such, become interested in the possibility of avian stepfathers. Cases in which the males will tolerate, and occasionally even help defend or feed, the previous male’s brood in order to increase his own chances of siring offspring come round two of egg laying.

            In a study done by Meek and Robert (1991) males in several pairs of Eastern Bluebirds were removed, and in over half the cases they were replaced by other males all of whom tolerate the previous male’s young. Several of those females later mated again with the “stepfather”, which worked our well for the males. Work done by Pinkowski (1977) may help explain the males tolerance to pre-existing broods due in that there is a high level of divorce within this species after early-season breed failures, meaning that tolerance may produce more offspring for the male than infanticide would.

Male Eastern Bluebird feeding chicks

            A study that was supposed to examine single mother chick rearing in Black-billed magpies ended up observing full parental care by replacement (or stepfather) males when they could not be caught and removed (Dunn and Hannon 1989). Four of the eight stepfather replaced the previous male when the female was no longer fertile, so there wasn’t even a chance that the stepfather may have had partial paternity for the brood. This phenomenon of stepfathers in black-billed magpie’s has also been observed several other times outside of studies.

Black-billed Magpie

            Clearly not all males are very tolerant of another male’s brood monopolizing a female they could mate with. Tolerance to the offspring isn’t quite the same as an actual father’s love either. Or caring. Close enough in the animal kingdom. However, as the magpie shows humans may not be totally isolated in caring for another guys kids, though goodness knows there is a LOT of research needed to be done to totally understand the motivations of the feathered stepfathers for not just kicking those eggs out. 

References

Dunn, P. O. & Hannon, S. J., 1989. Evidence for obligate male parental care in black-billed magpies. Auk 106: 635-644

Meek, S. B. & Robertson, R. J., 1991. ‘Adoption of young by replacement male birds: an experimental study of eastern bluebirds and a review’. Animal Behaviour 42: 813-820.

Pinkowski, B. C. 1977, ‘Breeding adaptations in the eastern bluebird.’ Condor 79:289-302.

Pictures
Bluebird: http://www.carolinabirdclub.org/gallery/Duyck/eabl.html
Magpie: http://www.fws.gov/northdakotafieldoffice/bhotline/nd_birding_hotline_rep_jan08.htm

It Pays to Have a Wingman

In most courtship displays or leks male birds are competing with one another, attempting to show off and prove their superiority even if they know they are not the strongest or the fittest individual there. It’s pre-programmed for them to face off. This is what was originally theorized when people watched the Lance-Tailed Manakins performing.

Lance Tailed Manakins preforming.

However, this turned out not to be the case. Instead of competing with one another, the two males were actually undergoing an elaborate courtship display in which ones individual is the alpha and the other is the beta. In other words, the alpha bird had a wing-man to help him display and successfully woo females. This was more than a little baffling as the males were not related to one another, and altruism is rare in the animal kingdom and the beta males were willingly cooperating in these dances. So what does the beta male get out of this relationship if he isn’t mating himself?

Emily DuVal (2007) was curious enough to test it, undergoing several experiments which included genetic sampling and typing of birds and offspring, observation studies of the courtship displays, as well as an alpha removal experiment where the alpha male from each courting duet was removed for a time. 

The results were quite interesting. It was hypothesized that the territory (or display site) would eventually be passed from the alpha to the beta, yet the results found that the alpha role was not passed along in a linear fashion as proposed. Instead rather, it was concluded that within the complex social network of these birds the betas may be undergoing a sort of apprenticeship, learning from the alpha so later on they themselves can have a more successful courtship display as alpha. Additionally, the alphas are determined through that same complex social structure she mentions, where the birds that are essentially the best net-workers with the most social connections to other male Manakins are the ones who end up as alpha generally.

The courtship for the Lance Tailed Manakin is still not totally understood, but it is a great example of how not all mating displays are what the initially seem as well as that males can get along when the incentives are good.

Reference

DuVal, EH 2007, ‘Adaptive Advantages of Cooperative Courtship for Subordinate Male Lance‐Tailed Manakins.’, The American Naturalist, vol. 169, no. 4, pp. 423–432.

Video: http://www.youtube.com/watch?v=2OQq5P3PLCw

A Corkscrew By Any Other Name is Still Not Romantic

For most of the behaviors I’ve discussed so far there has always been some effort and choice in the matter of individuals mating. A male develops large plumage to entice a female to choose them, both sexes evaluate one another for health and have extra-pair copulations accordingly, and so on. However, nature isn’t all that nice most of the time and the avian world is not exception to that. Some species of bird have forces copulations, wherein the females have absolutely no say in the matter and are forced to mate with whichever male is strong enough to force the copulation. Ducks, as well as several other species of waterfowl, are well known for this forced copulation mating system and as such have developed some outright WEIRD strategies for both sperm competition as well as insemination avoidance.

Now at this point some of you will know what I’m talking about, but for the rest prepared to be baffled and be warned: there are graphic duck genitalia images ahead. But they’re really cool. Because male ducks have adapted to sperm competition by having corkscrew penises. Yes, you can go back and re-read that. In a mating system where force is the only factor is achieving a mating males are in essence taking a chance that any one female that have sex with will actually become pregnant with their offspring, as every other male in the pond is also copulating with as many females as they can find. As such, many males ended up with a corkscrew penis which, in the case of the Muscovy duck, is able to evert and become fully erect in 0.36s (Brennan, Clark & Prum 2010). The high explosive rate actually helps force the penis further into the vagina, and some species of duck even have brush like appendages along their penis in order to collect and in a sense, “scrub away” competitors sperm. 

 Male Duck shown with fully extended penis. They can reach up to 40cm in length.

Now this is all very impressive in itself, but it gets even more interesting when you look at how the females of these species have adapted to thwart the males. These species of waterfowl essentially have antagonistic sexual conflict, in that the females do not wish to copulate (I don’t think I need to elaborate on why) yet are continually forced into it by aggressive males. Well, the corkscrew shape of the penis didn’t just emerge from thin air. Female duck vaginas are actually also corkscrewed in shape, just in the OPPOSITE direction. At some point in more recent evolutionary time the direction of the vaginal geometry flipped, making it more difficult for the males to successfully fertilize the females. The same study done by Brennan et al on the explosive time also looked into the effectiveness of the penetration of those males into different shapes. They used glass tubes to see how far the penis was able to reach in what must have been the oddest experiment done to date.

They tested a straight tube, a counterclockwise spirals which matched the male penis chirality, and finally they tested a clockwise spiral and a 135˚ bend. The last two mimicked actual vaginal geometry found in Muscovy ducks, and they found that the penis was far less successful in reaching any great depth into those tubes compared with the straight and counterclockwise spirals. This supports the idea that difference in corkscrew direction coevolved between the two sexes of many waterfowl species. The rather abused ladies had found a way to fight back. 
 

Example of oppositely spiraled genitals as well as the tubes used.

What’s more, in some species of duck females have even been found to have several “dead ends” in their vaginal tracks. Enfolds of the vaginal lining provide a sort of diversion to the penis, which can get re-directed into pockets that lead nowhere and store the sperm away from any of the actual eggs. This prevents fertilization while allowing the male to believe that he has successfully fertilized that particular female and move along.

So there you have it. Nature is not always pretty, but when organisms are faced with extreme challenges they will adapt, even if it’s to defend against their own species. And some of those adaptations can be pretty screwy!

References

Brennan, PLR, Clark, CJ & Prum, RO 2010, ‘Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia’, Proceedings of the Royal Society B: Biological Sciences, vol. 277, no. 1686, pp. 1309–1314.

http://www.kiwiblog.co.nz/2012/10/the_ducks_will_get_you_in_the_end.html

http://blogs.discovermagazine.com/notrocketscience/2009/12/22/ballistic-penises-and-corkscrew-vaginas-the-sexual-battles-of-ducks/

Timing is Everything

While there is a huge diversity of behaviors birds use during mating, it is important to remember that in many cases there are outside factors that can affect them that may not be obvious at first. For instance, Bearhop et al (2006) have fairly recently done some interesting work on migration. Specifically, how the migration of the European Blackcaps may end up undergoing speciation in the long run.

The European Blackcaps are a species of European passerines, a fairly common little bird found across Eurasia and northern Africa, have historically bred in south central Europe. However, instead of migrating to Iberia and Northern Africa for their overwintering grounds a rapidly increases number of the birds are showing up in the British Isles. And as time goes on, it seems that they are staying.

Bearhop and his colleges used a stable isotope technique for tracking these birds across their migration distances, something that had previously been quite difficult as Iberia and the British Isles are a fair distance away from one another and these birds are rather small. Lots of room for error and lost birds. However the stable isotope technique allowed them for the first time to get accurate, traced results and what they found could have some interesting long term implications.

They found that there is a genetic basis for the new migratory pattern displayed by the birds overwintering in the British Isles yet still returning to the south central Europe breeding grounds. And their numbers are growing, hinting that there may be some benefit towards fitness to change up the overwinter areas.

European Blackcap at a feeding table.

There are several reasons why the birds heading to the UK and Ireland may be experiencing higher fitness. The level of urbanization is quite high, presenting easy access to food from feeders, rubbish bins, as well as exotic plant species which fruit and flower more frequently throughout the year. The shorter migration distance is less energetically exhausting, and some have even theorized that the colder climate better prepares the birds for the early breeding ground climate upon their return. However, what may be the most important observation is that critical photoperiods during juvenile development that trigger gonad development occur in northern climates about 10 days earlier than the ancestral breeding ground.

That change shifts the development and breeding cycle of the birds up by several days, triggering migration back south sooner than those in Iberia return north. What we’re seeing is assortive mating being driven by a genetically driven behavioral change. This could, over time, isolate the species by migration pattern, and eventually even lead to speciation as the change is genetically driven.

So there you have it, a gene change for migration behavior may lead the European Blackcap to speciate sometime in the future. A time that may not even bee that far away really, as the migration change of birds towards the British Isles has rapidly occurred just over the past 60 years or so!

References

Bearhop, S, Fiedler, W, Furness, RW, Votier, SC, Waldron, S, Newton, J, Bowen, GJ, Berthold, P & Farnsworth, K 2005, ‘Assortative Mating as a Mechanism for Rapid Evolution of a Migratory Divide’, Science, vol. 310, no. 5747, pp. 502–504.

Picture: http://www.burdr.com/2009/12/blackcaps-adapting-to-a-new-migratory-path/

The Hidden Glow

Okay, this is probably one of the coolest things I’ve learned about any bird mating in the past three years.

Now that I’ve raised the bar far to high for myself, enter: the Eurasian Blue Tit. A bird easily identifiable due to their bright yellow and blue coloration. The sexes of this species have always thought to be indistinguishable from one another, much like the Albatross, without genetic sexing. Only the most experienced handles are able to tell the difference, and even then only with the bird in hand.

A Eurasian Blue Tit

However, recent work done by a group of researchers in Sweden decided to look outside the box, and from the bird’s point of view. To be specific: in the UV scale. There are several groups of bird which view light within the UV spectrum, one of which is the passerines (which includes the Eurasian Blue Tit). Andersson, Örnborg, and Anderson (1998) thought to examine the markings of this species at a UV scale, which is a while new spectrum of color and light that humans cannot see without the assistance of special cameras, lenses, and other technological aid.

Turns out, the Blue Tit is in fact sexually dimorphic, simply on a wavelength that we are unable to see. They found that the males have a marked difference of the chroma on their brilliant crown patches. And oh how I wish they had taken pictures of the marking! It was even proven to stand out against both brown-grey and bright green backgrounds, translating into contrast with either tree foliage or even the dead leaf litter on the forest floor.

This find could potentially be the explanation for several behaviors and displays these birds are known to exhibit. For instance, this species is known to be polygamous, with females seeking extra-pair copulations with healthier males. The scientific community were unsure as to how the females decided which males were healthiest, with theories including certain vocalizations in song and even leg length, as it was the only determinable trait they could find between mate choices. Now it seems that the UV coloration is what is selected for, which is supported by the fact that during mating and territorial displays the males display their crown patches to females and other males.

Just goes to show there is more than meets the eye when it comes to bird behavior. 

Bonus: This is a direct quote from the journal article.

“Although hardly perceivable in the field (except when directly compared in the hand) to the UV-blind and yellow-biased primates that write ornithological handbooks…”

References

Andersson, S., Örnborg, J., Andersson, M., 1998. ‘Ultraviolet sexual dimorphism and assortative mating in blue tits’, Proc. R. Soc. Lond. B., Vol 265, p. 445-450.

Picture: http://www.raywilsonbirdphotography.co.uk/Diary/2010/December_2010.html

Flower Petals for Romance (We Think)

Last week I talked about the highly monogamous albatross, who will form long term pairs even when mates of the opposite sex aren’t available. This week I decided I’d address a species who are socially very monogamous, yet cheat on one another relentlessly.

Fairy Wrens are a group of birds that are quite common in Australia, and are well known for the iridescently bright plumage on the males. All species of the group are socially monogamous, pairing together for years on end with a very low divorce rate, and raising offspring together. However, not all those offspring are biologically the father’s. Sexually the Fairy Wrens are quite promiscuous, and from this a rather odd behavior has arisen.

Males of several species of fairy wren, notably the Red-Backed Fairy Wren, have been observed carrying colored petals of either pink or red in their beaks when pursuing females. The petals either help enhance their nuptial colors, or as the case of the Splendid Fairy Wren who is a bright blue act as contrast to their coloration.

Splendid Fairy Wren with a light pink petal for display.

There was a question at one point as to whether the petal displays were for courtship, or for as a territorial display towards other males in their territories. This was tested by Karubian and Alvarado (2003), but they were unable to come to any true conclusion on the matter.

Their results showed that while the males with petals only presented them to other males about 10% of the time, the amount of time females spent with males was not any different with the petal or without. This is interesting because it seems to be an arbitrary behavior the males have evolved which do not provide any direct advantage in increasing their mating chances with their mate or for extra-pair copulations, nor in keeping other males away from their territories.

There is always a chance that this behavior is a relic of a past mating strategy that required more displays and potentially gifts. It could also be a remnant of a time when these birds were more sexually monogamous, and using petals to show off their own fitness was a way to ward off competitors. Or, fairy wrens just like petals! This is one of those interesting cases when a notable behavior is seemingly unexplainable, though quite obviously tied to romance. As all flower petals should be, really.

References

Karubian, J & Alvarado, A 2003, ‘Testing the function of petal-carrying in the Red-backed Fairy-wren (Malurus melanocephalus)’, Emu, vol. 103, no. 1, pp. 87–92.

Picture: http://dailyorganism.blogspot.com.au/2011/08/splendid-fairy-wren.html

Mateless in Hawaii

             Albatross are almost synonymous with monogamy in the bird world, they are the poster child for long term breeding pairs and obligate dual parenting of chicks. Both genders also happen to look the exact same. So it came as a bit of a surprise to some researchers when they went out and decided to genetically sex a population of Laysan Albatross and discovered that there was a serious gender skew on the island, and even MORE shock when the realized what exactly that gender skew had wrought in terms of social behaviors. 

            I’m talking about the population of Laysan Albatross on Oahu Island in Hawaii that is 59% female, of which 31% of the breeding pairs are female-female. This is big, and the reason this is big is because every single female-female “breeding” pair were completely unrelated to one another.

            Cooparative breeding does occur in nature, wherein others of the species pitch in to help rear offspring which are not directly their own. However, in essentially every case of this type of behavior the offspring being reared or the parents being helped were in some way related to the helpers. But that is not the case on Oahu!

            Monogamy SHATTERED right?! Wrong. It turns out that in this male-barren land the unpaired females have managed to get the monogamous male albatross to have extra-pair copulations (Okay, monogamy a little bit shattered) in order to breed themselves. In one study done on the success of the female pairs it was noted that almost half the female-female pairs were together for the full 4 years of the study’s duration (Young, Zaun & VanderWerf 2008). They even found from another researcher that one pair of ladies had been together for a full 19 years, indicating that they chose the homosexual rearing strategy over the traditional one.  

Female-Female breeding pair of Laysan Albatross

 

 

            While the female-female pairs had less success in hatching the eggs than the male-female pairs, of the chicks that hatched the survival rate was essentially equal. Those pairs staying together for more than one year had at least one offspring from each parent hatch and fledge. That alone means that both females agreed to this continued cooperation. A sort of you hatch my egg I’ll hatch yours system that is essentially based upon a mutual agreement. 

            All in all, these same-sex pairs of Albatross have adapted to their new “environment” by recognizing that some reproductive success with another female is better than NO reproductive success by not breeding at all. It was decided by Young et al that while the Albatross’ social behavior has shifted to include same sex pairs, they are still operating under their monogamous instinct. Which is working for them. It also goes to show how dramatically gender ratios can affect the behavior and reproductive strategies of a species in a relatively short amount of time. 

Personal hypothesis as to why there are so few male albatross on Oahu.

 

References

Young, LC, Zaun, BJ & VanderWerf, EA 2008, ‘Successful same-sex pairing in Laysan albatross’, Biology Letters, vol. 4, no. 4, pp. 323–325.

Pictures:

http://esciencenews.com/articles/2009/06/16/same.sex.behavior.seen.nearly.all.animals.review.finds

http://www.timdrussell.com/pythonstills.htm

Feet Don't Lie

          I have a personal love for the foot coloration and courtship displays of the Blue Footed Booby. As the name suggests, the species is most notable for the brightly colored feet found on both males and females in addition to the infamous “Booby mating dance” in which the males lift their feet as high as possible to display their color to the female. This added to sky pointing and presentation of nesting materials (an artifact of ancestral behaviors as these birds don’t actually make nests any longer) can net a male Booby a mate for the breeding season. But the foot color is key in these displays, and this is because it is an incredibly honest indicator of both how well fed they are as well as their immunological state.

Male Blue Footed Booby lifting feet during courtship display.

The colors of feet range from blue-violet to bright green-blue, with the greener feet belonging to those individuals who are healthiest. One study was able to document the drastic reduction in vibrancy of the pigment in the feet from bright green to a dull blue-violet over the course of 48 hours when deprived of food (Velando, Beamonte-Barrientos, & Torres. 2006). Such a noticeable change makes it quite apparent to females whether their suitors are healthy, and vice versa as the female foot coloration is just an honest an indicator of health as the males. This is where it starts to get interesting in terms of reproduction.

Example of the difference in foot coloration amongst Blue Footed Boobies

Blue Footed Boobies are socially monogamous birds, and actually continue to undergo courtship displays after breeding has occurred. This isn’t the result of sentimentality, or of male blue-footed boobies being overly romantic. It is actually each member of the breeding pair checking up on the health of their partner and deciding whether or not it’s worthwhile to maintain the pairing. Should one of the pair find that their partner is “letting themselves go” in any way the results can actually be pretty dramatic.

Female boobies lay anywhere from 2-3 eggs a season, with the average being 2 laid several weeks apart. The same study on foot color by Velando, Beamonte-Barrientos, & Torres (2006) found that during that intermittent time frame between laying, if she discovers her mate is starting to drop in health she will actually adjust the amount of energy and nutrients she puts into producing offspring to result in an egg that is greatly reduced in size.  Essentially, the female puts in so little effort to egg formation that the offspring is almost assured not to hatch. If the female does not believe that the male can adequately help rear the offspring she simply ceases having them. All based on the color of his feet.

It’s not unheard of that females control their clutch sized based on environmental factors or mate quality, but in this case all the same requirements put upon males by females apply directly to them as well. In a study done by Torres and Velando (2005) it was found that females with duller foot coloration received less post-copulation courtship displays as well as fewer extra-pair copulations. Their own mates were also more likely to seek extra pair copulations with females who have brighter foot coloration.

             Essentially, the blue feet were selected for through sexual selection on behalf of both the male and the female of the species. Which makes sense, as their chicks require a long period of biparental care after hatching to rear them to independence. In many cases with birds only the males are pushed by female preference into large showy plumage, so I find it interesting when in nature you a find a sort of equality in the expectations of both males and females for brood rearing.

References:

Torres, R., Velando, A. 2005, ‘Male preference for female foot colour in the socially monogamous blue-footed booby, Sula nebouxii’. Animal Behavior, vol 69, pp. 59-65.

Velando, A., Beamonte-Barrientos, R., Torres, R. 2006, ‘Pigment-based skin colour in the blue-footed booby: an honest signal of current condition used by females to adjust reproductive investment’, Oecologia, vol 149, pp. 535-542.

Picture Credit

Dance: Personal Picture

Darker feet: http://photography.nationalgeographic.com/photography/photos/life-color-blue/#/blue-

                     feet-laman_1331_600x450.jpg

Lighter Feet: http://www.galapagos-islands.com/what-to-see/blue-footed-booby.html

The Funny Thing About Leks

There is a huge question still in evolutionary biology, which concerns the absurdly high degree of sexual traits (such as the tail of a peacock) of males who form leks. Now, a lek is when a large group of males all get together in a huge group and display for females, who then come and choose who they wish to mate with, and then promptly leave.

Females who visit leks almost always choose the same male to mate with, and that male is generally the one with the largest display, usually of plumage. The larger and more extreme these display traits are however, the lower the chances are of male survival. So the big, baffling question is why would females prefer these large displays, which increase the chances of death to the male, when they receive no other benefit than simply sperm?

A Sage Grouse lek, with displaying males.

In a review article written by Mark Kirkpatrick and Micheal J. Ryan (Kirkpatrick & Ryan 1991)on this very subject, they discussed three of the larger hypothesis about this behaviour. Spoiler Alert: We still don’t know which is the driving force behind extreme sexual displays and lekking! Which is why I personally think it’s pretty cool.

The first hypothesis essentially a direct selection by females on males, where the males with the largest displays get the most copulations wholly for selfish reasons on the female part. This means that the preference of larger displays by females is because, even though those traits increase the chances for the males of dying, choosing those mates will increase the females chances for survival or to reproduce themselves. For example, mating with larger, flashier males may reduce the pressures of searching for and choosing a male for the female. In addition, there is another very important factor called pleiotropy, which is when a gene associated with higher survival of the individual also affects that individual’s preference for mates. This means that a certain gene that may make a female bird of paradise REALLY like males with huge plumage also helps boost its immune system, or something similar. Since that gene is going to be kept, because it’s very helpful, that means the preference stays and the females will select for the males that meet that preference whether it’s good for the males or not.

Another hypothesis that was discussed in the paper was termed the “Runaway Process”. In this case it is thought that a sexual trait is linked to a gene, meaning that quality of environment or amount of food obtained doesn’t make the feathers brighter or longer. Essentially, the sexual trait appears and females select a bit for it and after a few generations almost the entire male population has developed this trait due to selection. The ever-present preference for the largest, most stunning trait will cause that trait to evolve to be bigger, brighter, more magnificent than any other male in order to meet that demand of the females no matter the consequences! Which is, as always, a higher mortality rate for the males. But now that the preference for the largest trait has been established, it will just continue to increase in speed like a runaway train. Smaller populations usually provide results that support this hypothesis, and the affects of genetic drift in those smaller groups most likely play a large role in establishing the immediate increase in the presence of a sexual trait by males.

The final hypothesis is based on a concept that is pretty familiar with most people, in that the brighter and bigger the bird the healthier he his and the stronger his genes for survival are. Also known as the parasite hypothesis, which is confusing until you think that the better a bird is at fighting of parasites that cause disease the healthier they are.  So those birds that look the best are probably free of parasites and have stronger immune systems. So by congregating in large numbers, they are better able to show off that they are brighter than other males, and increase their chance of mating.

Now, there are many other hypothesis about why certain displays have evolved over time, but I personally thought this article did a fabulous job explaining them. It goes on to explain why we are so unsure as to which one is true, and ways they think we should test it. I personally feel as though the runaway hypothesis is fairly week, and would be most likely to back the first one in which pleiotropy is correlating preference to female survival, but then I have never been one to immediately agree with parsimony.

 Original Review Article:  

Kirkpatrick, M & Ryan, MJ 1991, ‘The evolution of mating preferences and the paradox of the lek’, , Published online: 07 March 1991; | doi:10.1038/350033a0, vol. 350, no. 6313, pp. 33–38.

Picture Credit:

‘Eco-Vocab: Lek’ The Olive Tree, accessed February 25, 2014, from <http://oleaeuropea.wordpress.com/2011/01/25/eco-vocab-lek/>.