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Twit Twoo

By Laura Hooper

Photo credit: Naturepicsonline, Wikimedia Commons

It is that time of year again when all the shops are full of hearts, roses and fluffy teddies with declarations of love printed on their tummies. Gifts are one of the ways we as a species attract or keep a partner. But how do other members of the animal kingdom pull it off?

Within the animal kingdom there are two main ways that animals find a mate. In one instance the females may choose a male partner. This is called intersexual selection, and is the process of courtship (which is the main focus of this article) [1]. Alternatively, intrasexual selection may occur where males compete over access to females, for example elephant seals fight to become ‘beach master’ [1].

Courtship displays are a set of species specific behaviours with the sole purpose being to attract a mate for copulation (mating), [2]. These displays provide a clear communication of intention between the sexes, and as they are different depending on species, it also ensures mating of the same species. For example a mutual display may be carried out whereby both sexes perform responsive or synchronised displays. Not only does this allow species recognition but it also facilitates bonding. Mutual displays are common for bird species for example, Crested Auklets perform a vocal mutual display by cackling to one another [2].

It is often the males that will begin a courtship display and exhibit many behaviours to impress and attract females. In fact many of the sexual dimorphisms you witness, such as males being more brightly coloured, are due to the different roles the sexes play in courtship [3]. So why is it that the males go to all the effort? The answer lies with the difference between the sexes in gamete production (production of eggs and sperm). Female displays are so rare because displays are very energetically costly [2]. Females have already put a lot of energy in to egg production and, as few are made each carry a high investment [4]. Comparatively males produce many sperm and invest little energy in each one. In addition, there is a difference between the sexes in relation to the variance in mating success. This is known as Bateman’s principle [4]. The variance in mating success between females of a population is low as they only really need to mate once and the probability is that their eggs will be fertilised. However, there is a high variance between males as their reproductive success is generally based on the number of times they mate (see graph) [4]. Usually a few males will mate with many females thus having a high reproductive output, but most will have little or no output. Also, in systems where multiple males and females mate with each other (polygynandry), males need to ensure it is their genes that are passed on, so the more mates they have the higher the chance they have of doing this [4]. This therefore means that if a male can mate with a large number of females he will have a higher reproductive output. This is why it is believed that males have developed behaviours and characteristics for courtship over females as they need to attract mates [5].

Photo credit: [4]

The fact that females’ gamete production is more energetically costly also makes them more discerning when it comes to picking a mate. This is because to increase the likelihood of survival of the offspring a good mate must be selected. It is for this reason that courtship displays are so important; it is a chance for males to show off their desirable characteristics to females. There are several hypotheses proposed to describe how females pick a mate. One is called the ‘good gene model’ [5]. This is where females may pick males with certain desirable traits, for example if they have resources like good territory to support offspring development. Or the males that have the brightest feathers show they have superior foraging ability, the brightness is due to them consuming more carotenoids, found in fruit etc. [5]. Another hypothesis is the ‘handicap hypothesis’. Many features of courtship are actually very risky for males, such as having very bright markings which makes them more visible and therefore more vulnerable as prey. Although they may be a risk for males, they are attractive to females as they signal the ability of the male to cope with the handicap [5].

Courtship displays usually involve a dance, vocalisations or maybe displays of beauty (e.g. bright colours), or strength [2]. Some animals may also release pheromones to signal their availability [3]. The following are some specific examples of behaviours and displays:

Male Bowerbirds

Instead of having physical characteristics, these birds display by building ‘bowers’ which are colourful shrines. A lot of time and care is put into the construction of these, with a lot of work being done to gather objects for decoration. Examples of objects used in these bowers are; flowers, berries, coins, glass, shells and plastic, (see image). The female will choose the most artistic [6].

Photo credit: [7]

Hooded Seals

Males of this species have evolved a red nasal cavity that they can blow up. They also bounce the inflated sack around as part of the display. Females are attracted to the males they deem to have the superior or most alluring nasal balloons [6].

Red Capped Manakin

The males of this species perform an impressive looking mating dance, coupled with specific sounds such as clicks [6]. See video below:


But it is not just exotic animals that take part in courtship rituals, in the UK there are many examples, which I am sure you will have witnessed at some point. A very common sight in towns and cities throughout the UK are pigeons. I am sure you have seen many times a seemingly desperate male parading in front of a disinterested female? This is part of their courtship display, in order to attract a mate or even to reinforce a bond between already paired pigeons they carry out a number of behaviours, including the following; Bowing, where the male puffs out his neck feathers and lowers his head. Tail-dragging, spreading of the tail and dragging it along the floor as they run after a female [8]. There are approximately 19,000 breeding pairs of Tawny owls in the UK. Their courtship begins in late February. At this time the male changes his hunting habits to catch prey more frequently in daylight hours so the food can be presented to a female. In addition, as he patrols his territory he may screech to repel rival males and to attract females [9].

Photo credit: [10], [11]

Animals may not be able to pop to the shops to buy a bunch of roses to show their intentions, but that doesn’t stop them giving ‘gifts’ of their own! These ‘gifts’ are presented in some species by the male to try and ensure that copulation occurs. Spiders may wrap prey in silk parcels to present. Male Paratrechalea ornata spiders will also incorporate a pheromone into their silk wrap to encourage the female [12]. Kingfishers will give fish as a gift; it has been found that females are fussy over both the size and species of the fish being gifted. The male will first swallow the fish so it can be presented to the female face first. From experimental investigation it has been discovered that males who produce gifts may be choosier in picking the right female to give it to. This is because, similarly to female egg production, producing good gifts is energetically costly so they don’t want to waste them on a non-viable mate [12].

Overall, there are many different ways that animals attract partners. From dancing, to building shrines and even giving gifts. All with the sole aim of being able to mate and pass on their genes to the next generation.


References

  1. ‘Animal Behaviour’, Shmoop. Available from - http://www.shmoop.com/animal-behavior/mating-behavior.html Accessed 07.01.16
  2. ‘Courtship Display’, Wikipedia. Available from- https://en.wikipedia.org/wiki/Courtship_display Accessed 07.01.16
  3. ‘Animal Reproduction/Courtship’ Shmoop. Available from - http://www.shmoop.com/animal-reproduction/courtship.html Accessed 07.01.16
  4. M.O. Krasneck, C.N. Cook and M.D. Breed (2012). ‘Mating Systems in Sexual Animals’ Nature Education Knowledge 3 (10):72. Available from - http://www.nature.com/scitable/knowledge/library/mating-systems-in-sexual-animals-83033427 Accessed 07.0.16
  5. ‘Courtship Rituals in the Animal World’ by Brian Kateman (Dec.2010) State of the Planet Columbia University. Available from - http://blogs.ei.columbia.edu/2010/12/01/courtship-rituals-in-the-animal-world/ Accessed 08.01.16
  6. ‘9 of the most bizarre animal mating habits’ by Bryan Nelson (June 2013) Mother Nature Network. Available from - http://www.mnn.com/earth-matters/animals/photos/9-of-the-most-bizarre-animal-mating-habits/strange-love#top-desktop Photos 3, 6 and 7 used. Accessed 08.01.16
  7. Bowerbird ‘Bower’ - https://commons.wikimedia.org/wiki/File:Bowerbird_bower.jpg Accessed 13.01.16
  8. ‘Pigeon courtship: romance is alive!’, Pigeons as pets. Available from - http://www.pigeonsaspets.co.uk/2011/01/02/pigeon-courtship-romance-is-alive/ Accessed 09.01.16
  9. ‘Tawny Owl’, Wild Owl. Available from - http://www.wildowl.co.uk/tawnyowls.html Accessed 09.01.16
  10. First Pigeon picture: https://commons.wikimedia.org/wiki/Category:Pigeon_courtship_and_sex#/media/File:Pigeons_11_2012-07-07.jpg Accessed 13.01.16
  11. Second Pigeon picture: https://commons.wikimedia.org/wiki/Category:Pigeon_courtship_and_sex#/media/File:Pigeons_12_2012-07-07.jpg Accessed 13.01.16
  12. ‘Love gifts in the animal kingdom’ by Ella Davies (February 2012), BBC Nature. Available from - http://www.bbc.co.uk/nature/16987410 Accessed 09.01.16
  13. Header image: https://commons.wikimedia.org/wiki/Category:Bird_courtship?uselang=en-gb#/media/File:Morus_bassanus_billing.jpg Accessed 30.01.16

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