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/