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