A Trip Which Sparked Curiosity (Part 2)


The Infamous Horned Bill – Combining Physics And Biology In One Beak

Continuing on my travelimages around the Natural History Museum, I came across an odd shaped beak, cut in half. The main beak was structured how one would expect it to be structured – a curved shape with a spiderweb of bone fibre strands inside – however, the addition of, what I now know to be called, a casque confused me. This hollow mound atop the beak ignited the curiosity inside me, leading me to write my second post in this series about the gorgeous Rhinoceros Hornbills, and more importantly, the more practical functions of their striking beaks.

The Casque

The normal part of the beak is predominantly used how every other beak is used, nothing much unusual to report here, so rather than take you all through the “boring” part of the beak, I decided to only discuss the more extraordinary casque.

Acoustics

The main theory about the function of this weird structure is that it is used almost like a resonance chamber[1], to amplify the sound of the Rhinoceros Hornbill’s call.

The casque is a perfect shape to allow a certain number of whole sound waves to fit into it. This length is different for each species as their calls are different pitches, and the sound waves produced, therefore, have different wavelengths. When the bird then calls, some of the sound waves produced enter the casque. As more sound waves enter, the crests of these waves line up and produce a resultant wave with the combined amplitude of the initial waves. This has a resonating effect and the sound is therefore amplified.

Reinforcement

The casque is said to have reinforcement properties as well. Not only does it add structural integrity to the beak, but also adds weight to make the beak a more effective hammer[2], which is useful when cracking open the tough exoskeletons of insects, and when the female and offspring break out of the enclosed nest (see ‘brief side note’ below).

Another use for this splendid casque is in aerial jousting [3] – a competition males engage in for territory and mates – which is pretty much exactly what it sounds like. Two males fly at each other at great heights and clash casques, so the reinforcement comes in handy; protecting the birds from major injury.

Sexual Attraction

The casque not only has purely practical purposes. A large element is attracting a mate. It is the casque in Rhinoceros Hornbills which exhibits sexual dimorphism – the size of casque differs between male and female[3]. This differs between species; in some species the males have bigger casques, but in others the roles are reversed, and some species are even monomorphic (only one size of casque is present). However, the interspecies differences are driven by sexual selection pressures, as some species’ casques may have evolved to allow them to excel in other areas.

The casque’s colours are also important in sexual attraction. When the Hornbills are born, their beaks and casques are white, like our fingernails. However, as they grow older, they rub their beaks against an oil gland just underneath their tail feathers, imagesecreting an orange oil onto the beak. The cumulative applications of this oil are what create the tremendous bursts of colour on the beaks. This allows individuals to recognise each other and sometimes is helpful in visual signalling as well [2].

Although not always the case, sexual dichromatism can occur as well. As I discussed in my previous post about the King of Saxony bird of paradise, sexual dichromatism is something which occurs in most birds. Some species of Hornbills exhibit this dichromatism through the colours and patterns created on their casques [2]. These factors all combine to create the perfect display in order to look as attractive to the female as possible.

Brief side note

As I mentioned previously, the females and their offspring have to break out of the enclosed nest which the Hornbill parents create. I thought I ought to discuss this further, not least because I find it a particularly fascinating element of the Hornbill’s behaviour.

Once the female and male have mated and the female is ready to lay her eggs, the pair find a hollow tree cavity, build a nest, and proceed to seal the female inside. They do this by creating a imagepaste made from fruit, faeces, and mud, squashing this through their beaks against the side of the cavity entrance. The pair completely seal the cavity except from a slit which is left for the male to pass regurgitated fruit through to keep the female alive while she sits on her eggs, and the offspring alive once they have hatched until they are ready to leave the nest. The female will also use this slit to expel faeces and uneaten food, in order to keep the nest clean [4].

Three months after the eggs have been laid, the female breaks out of the nest. Working with her life partner, she reseals the cavity so the offspring can be kept safe for another three months; until they are able to break out of the nest by themselves. Both parents take care of the offspring until this point [4].

Conclusion

Many of us may have grown up seeing these beautiful birds in zoos and on the TV, so the Rhinoceros Hornbill’s beak may be something that we are used to seeing, however, I hope that this post has given a bit more of an insight into the adaptations which make this bird’s beak perhaps one of the most interesting. I have been surprised at the level of sophistication that the seemingly useless mound that is the casque has demonstrated as a structure, delving briefly into the world of physics and then returning to the familiar realms of biology to fully discover the functions of the beak’s most peculiar feature.

 

[1]WORLD LAND TRUST. (2016) Rhinoceros Hornbill. [Online] Available from: http://www.worldlandtrust.org/education/species/rhinoceros-hornbill [Accessed: 18th November 2016]

[2]JACKSON, T. (2013) What is the function, if any, of a hornbill’s casque? [Online] Available from: http://africageographic.com/blog/what-is-the-function-if-any-of-a-hornbills-casque/ [Accessed: 19th November 2016]

[3]NAISH, D. (2014) The Splendid and Remarkable Anatomy of Hornbills [Online] Available from: https://blogs.scientificamerican.com/tetrapod-zoology/the-splendid-and-remarkable-anatomy-of-hornbills/ [Accessed: 24th November 2016]

[4]NATIONAL AVIARY (2016) Rhinoceros Hornbill [Online] Available: https://www.aviary.org/animals/rhinoceros-hornbill [Accessed: 27th November 2016]

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The Marine Iguana – what makes it so unique?

marine-iguana_robin-slater2

Similarly to thousands of others across the UK on a Sunday night, I was encapsulated by David Attenborough’s new TV programme, Planet Earth II. It was an hour which spiked my curiosity about one reptile in particular, the Marine Iguana, endemic to the Galapagos Islands. It caused me to take a look at what makes these so special, and so different from land iguanas.

These animals are not the prettiest, scaled and ancient in their appearance, however they do have some amazing ecological adaptations, making them truly unique. Surprisingly, despite their scary appearance they are herbivores, feeding as the only sea going lizard in the world [2]. Living on land but feeding in the oceans, Marine Iguanas feed on seaweed and algae, diving up to 30m and holding their breath for around 45 minutes [4]. As this is a habit unique to Marine Iguanas, it provides them with an abundant food source, allowing them to thrive on the Galapagos Islands [2]. Interestingly, it tends to be the male iguanas who feed under the surface, with female and young iguanas feeding on the algae from rocks on shore [3] – something I find somewhat chivalrous.

The temperature of the waters around the Galapagos islands mean that Marine Iguanas can never spend too long in the ocean, returning back to the warm of land as they are ectothermic, meaning they cannot regulate their body temperature, unlike mammals and birds [3]. This makes them much more reliant on the temperatures of their environment, warming in the sun and cooling in the shade – when it is cold, they move slowly until they have warmed up enough to feed, and when it is hot they actually physically cover each other for shade. At night, when the temperatures of the Galapagos Islands drop considerably, they gather in vast numbers to conserve body heat [3]. The temperature endurance of an iguana is truly remarkable, when feeding then can lose up to 10˚C of their body temperature [3] – a change which, in humans, can be fatal. For these exceptional animals, they merely bask in the sun to warm up.

So what is it that makes Marine Iguanas so exclusive and adapted to their environment? It’s their long and muscular tail, which moves in a sinuous motion to act a propeller, pushing them through the ocean similarly to crocodiles [3] and razor sharp teeth to scrape algae off rocks. They also have tremendously sharp claws to help them cling to rocks on shore and underwater, withstanding heavy currents – another adaptation to help them feed. However the adaptations don’t stop there, due to the salty nature of the seas, they even have salt glands connected to their nostrils which clean their blood of extra salt accidentally ingested whilst feeding underwater [1].

Almost every shoreline of the Galapagos Islands is scattered with Marine Iguanas, but these mysterious creatures differ from island to island. Marine Iguanas show their exceptional colours as they mature, with coal black young maturing into red, black, green and grey iguanas [2]. The most colourful of these is the Española Marine Iguana, who have earned the nickname ‘ Christmas Iguanas’ due to their festive colours. Breeding season, which varies again from island to island also has an impact on the colourings of these reptiles, predominantly the males. During this time, the males develop red patches, on ‘Hood Island’ the male will turn completely red, in order to attract a mate and appear the most superior [3].

These entirely unique creatures, found in such a small part of our world have some amazing feeding adaptations and as the only sea going lizard in the world, every effort should be made to preserve their species and environment. I think their behaviour is truly remarkable.

  1. http://animals.nationalgeographic.com/animals/reptiles/marine-iguana/
  2. http://www.galapagos.org/about_galapagos/about-galapagos/biodiversity/reptiles/#marine
  3. https://animalcorner.co.uk/animals/galapagos-marine-iguana/
  4. https://www.redmangrove.com/11-curious-facts-about-galapagos-marine-iguanas/

A BDG Manifesto

Today’s session started out in a similar procedure to all the previous BDG (Biology Discussion Group) sessions. The chair established the groundwork of the discussion/debate. Exchanges then took place in a civil and calmly manner for a major part of the session before all hell broke loose after a (not-so-accidental) controversial remark was made. And I for one have to say, it was GLORIOUS. Harry Delph was the first one to retaliate but a quick succession of heated exchanges between the religious and the heathens kept the spirit of the debate very much alive. Hannah Rushton, a fierce advocate of the environment and its complex ecosystems, made a very convincing case for the seemingly meaningless lives of starfish against grand design. Tarn, a believer whose faith is a force to be reckoned with, retorted with fiery fervour so intense she forgot she needed to breathe in those 30 seconds of righteous fury. The back-and-forth argumentation was a stark contrast to the initial 20 minutes of peaceful storytelling.

Today’s BDG sesh confirmed an inkling I have had about these weekly BDG congregations, namely, people actually look forward to BDG sessions in the days leading up to it. It’s not just a dour dialogue about highbrow academic topics. It is intense and passionate and loud and strong opinions are aroused during the course of these discussions. BDG is one of the few clubs where the role of peacekeeper is very much in demand. As far as I am concerned, it is not just a platform to discuss high-minded scientific ideas with impartial judgement; for many of us, it is catharsis. Sheer release of emotion. You can see it in how readily BDG members jump at the opportunity to voice their opinions. People have researched the topic and they’ve done their homework on the issue. They’re ready to show the results of their reading. Those lengthy monologues in our head culminate in a BDG session where it comes out in all its brilliant fury. There’s an element of spontaneity and also an informality in these gatherings that prevents these discussions from becoming too stilted. Not to mention the free food and the social aspect of these freewheeling dialogues.
I believe we’ve stumbled upon a magic formula here. BDG is that rare combination of being intellectually stimulating, socially accepting and most importantly, fun.
BDG is an appointed occasion for people to go on a verbal outburst without fearing the social consequences of offending someone. It is a designated time and place for people to explore and espouse radically different viewpoints that they normally would not.
Never in BDG has anyone walked away with bitter feelings. I think it’s important we acknowledge this in order to engage in these discussions more fully (e.g. I literally told Max to die in BDG today and we’re still friends – I think). What happens in BDG, stays in BDG.

What I’d like to propose is this, to outline the purpose of these Biology Discussion Sessions. By expressly articulating the purpose of BDG, I hope to clarify what these discussions are for, so that we can get the most out of these sessions. A BDG Manifesto that states clearly the objective of BDG itself. BDG is there for us to engage intellectually with scientific issues. The second, less obvious but equally important purpose of BDG is to serve as an outlet for all of the academic reading we do over the course of the week. If there is anything to show for our nerdiness; then it’s in these BDG sessions. Finally, (and this is the most important) the ultimate purpose of BDG is TO HAVE FUN. Because life is inherently meaningless, so we might as well have fun while we’re still here.
Peace out *mike drops*

The Giant Panda

image104I am an undoubted and avid Giant Panda lover, whether it be how much I secretly want to be able to eat and sleep all day or my desire to preserve such a species so close to extinction, I’m not entirely sure. Therefore, I deemed it only fitting that my first blog post should be about these creatures.
Somewhat surprisingly, the Giant Panda is incredibly well adapted to its environment, namely as a consequence of what I could only imagine to be a slightly monotonous diet of bamboo. One of the most evident of these adaptations is the ‘sixth toe’, actually an extension of the wrist bone of a Giant Panda. This gives the panda extra strength, which enables it to pull up shoots, pull off leaves and grasp bamboo. [1] This is crucial for a Giant Panda as 99% of their diet consists of bamboo shoots and leaves, [2] and thus being able to extract this plant easily is fundamental to their survival.

Pandas belong to the family of bears, the Urisdae family, and have a particularly well adapted jaw and head to again enable huge bamboo consumption, as it is a tough and firm plant. The jaw muscles of a Giant Panda need to be incredibly strong to chew such a plant (think of it as a human chewing toffee all day) and thus the cranial cavity of the giant panda has evolved to accommodate these larger jaw muscles [2], ensuring the survival of the Giant Panda as it allows for the vast consumption of bamboo, their main source of food.

Along a similar theme, the molars of a Giant Panda has evolved to be very large and frictionless, differing the Giant Panda again from the Urisdae family as it is a species which only uses its molars, whereas most other bears uses their canines to hunt and kill their food.

As eating is evidently what the Giant Panda is best adapted to do, the digestive system of a Giant Panda is also adapted to their favourite food, bamboo. The oesophagus of a Giant Panda has a tough lining to prevent tears, and the stomach is very strong and muscular as bamboo is a relatively hard food to digest, due to amount of cellulose it contains. For the same reason, unlike the rest of the Urisdae family the Giant Panda has a short intestine and a larger colon, as very little water is consumed by a panda each day and a very small amount of waste compared to the amount of food consumed.

Part of a Giant Panda’s undoubted charm is their slightly stocky appearance compared to most bears. Their legs have become more muscular and strengthened overtime, due to climbing trees for their average 20-40 pounds of bamboo a day [2]. As a result of this huge consumption of bamboo, Giant Pandas do not appear fragile, and actually weigh around 250 to 220 pounds [2] with their legs having to carry all this weight over long distances and up trees, for between 10-16 hours a day [2]. This is required to maintain the nutrition levels which are needed for the survival of pandas.

Consequently, while I can’t say my initial love of pandas came from their evolutionary features and not their ‘cute’ yet formidable appearance, it has certainly widened my interest and made them an even more fascinating creature – and yes, one I truly admire for their wholehearted commitment to bamboo.

1.    https://bioweb.uwlax.edu/bio203/s2007/barger_rach/adaptations.htm

2.     http://astridsecologyproject.weebly.com/pandas-physical-and-behavioral-adaptations.html