A lasting love affair with birds.

Seeing as this is the final blog post, I think it's time to reflect on what you have hopefully learned since my introductory blog. It is also a chance to sit back and enjoy the wonder of birds and consider, with the knowledge you now have, how much of that wonder can be attributed to sexual selection. By now you should be thinking about how many of the fascinating, elaborate, bizarre, beautiful and extreme behaviours and morphological characteristics displayed by birds are a result of the endless drive to reproduce.  

Sit back and enjoy this video showcasing some of the finest bird displays out there, https://www.youtube.com/watch?v=wTcfDCjBqV0. Viewed 18th May 2017.

While this blog has hopefully taught you a lot, for me it has prompted just as many questions as it has provided answers - and this is exciting! It means that it will be impossible to ever lose my fascination with birds when there is still so much we don't know. It is also humbling, and I think nice to know, that we will undoubtedly never fully understand the complexities of how and why birds have evolved the sheer behavioural and morphological diversity we see today.

 

Another video that should make you get out and about and see some incredible birds for yourself, https://www.youtube.com/watch?v=c2c8IhVRlvo. Viewed 18th May 2017.

 

So, next time you are looking at a bird, have a think about why it looks, sounds and behaves the way it does. Can you relate any aspect of what you see to how it may be used to attract or choose a mate? If the answer is yes, which I hope it is, I have achieved what I wanted through writing this blog. Over the years I have had people ask me, "Why do you love birds so much? They are so boring". Boring, are they serious???!!! Do they walk around with their eyes and ears closed? I am biased of course, but I find it incomprehensible that someone could see some of the birds I have seen and the behaviours they display and still not be in awe of them. So get out there and see for yourself some of nature's finest work - the bird world in all its glory and mystery.

I have seen all of these beautiful Australian birds, all of which can be found locally in North Queensland. Photo by Jonathan Munro http://www.wildwatch.com.au/birdwatching. Viewed on 19th May 2017.

 

Sex role-reversal in birds - an exception to the rule

Every blog post I have presented so far has talked about males competing with one another for females, and referred to the choosy sex as the female. While this is predominantly the case, with females providing in most cases greater postfertilisation care, what if this wasn't always the case? Are there certain environmental conditions and community dynamics that would favour sex role-reversal? If this was ever the case and reversal in parental care is strong enough, the direction of sexual selection may become reversed and act upon females more strongly than males (Emlen & Wrege 2004)

Jacanas are exceptional in that seven out of eight species of the family Jacanidae exhibit highly developed sex role-reversal (Butchart 2000, Emlen & Wrege 2004). Males of these species are the sole incubators of eggs and provide the majority of care for the dependent young (Butchart 2000, Emlen & Wrege 2004). Jacanas also display the most extreme reversal of sexual size dimorphism of any other group of birds or mammals, with females weighing up to almost 50% more than males (Butchart 2000). Polyandry has been well documented within the family, with females mating and providing clutches for several males while defending their exclusive territories (Butchart 2000).

Female Bronze-winged Jacanas (Metopidius indicus) are generally more than 60.3% heavier and behaviourally dominant to males, which carry out all the incubation and chick care. Photo by Rupal Vaidya https://alchetron.com/Bronze-winged-jacana-1982762-W. Viewed on 10th May 2017.

The Wattled Jacana (Jacana jacana) is a perfect example of a sex role-reversed bird. Not only do they show all the characteristics mentioned above, females also display greater development of secondary sexual characters such as wing spurs and fleshy facial ornamentation and are more behaviorally dominant than males (Emlen & Wrege 2004). Intrasexual competition between females to accumulate multiple mates is often intense, with larger, more ornamented females shown to hold more territory and have more mates (Emlen & Wrege 2004). Studies have indicated that sexual selection is indeed operating more strongly on female Wattled Jacanas (Jacana jacana) than males (Emlen & Wrege 2004). 

The Wattled Jacana (Jacana jacana) is a great example of a sex role-reversed bird - females compete for males, have developed greater secondary sexual characters and have abandoned nearly all parental care. Image sourced from http://photography-on-the.net/forum/showthread.php?t=1284873. Viewed on 10th May 2017.

So why has the Wattled Jacana (Jacana jacana) developed sex role-reversal? A combination of two main factors has been suggested. Clutch predation of about 50% has selected for females to produce multiple clutches and a tropical climate has allowed for low levels of incubation (Butchart 2000, Osborne 1982). This, coupled with the production of precocial chicks has allowed females to invest less in parental care and more in reproduction (Butchart 2000, Osborne 1982). While this explains how and why polyandry may have developed, it still does not explain exactly why males display greater parental care than females (Butchart 2000). Whatever the reason, it appears to be a successful strategy for the Jacanidae family that has evolved a way in which to tailor their breeding strategy to their wetland environment. I spent a lot of time watching Comb-crested Jacanas  (Irediparra gallinacea), in Kakadu National Park - they are known as "Jesus birds" as they appear to walk on water!

The Comb-crested Jacana (Irediparra gallinacea) is one of the seven out of eight species in the family Jacanidae that exhibits sex role-reversal. It is also known as the "Jesus bird" as it appears to have the ability to walk on water. Photo by David Taylor, http://www.hbw.com/ibc/photo/comb-crested-jacana-irediparra-gallinacea/comb-crested-jacana-struck-lovely-pose-amidst. Viewed on 9th May 2017.

References

 
Butchart, S.H.M. 2000, "Population structure and breeding system of the sex‐role reversed, polyandrous Bronze‐winged Jacana Metopidius indicus", Ibis, vol. 142, no. 1, pp. 93-102.

Emlen, S.T. & Wrege, P.H. 2004, "Size dimorphism, intrasexual competition, and sexual selection in Wattled Jacana (Jacana jacana), a sex-role-reversed shorebird in Panama", The Auk, vol. 121, no. 2, pp. 391-403.

Osborne, D.R. 1982, "Replacement nesting and polyandry in the Wattled Jacana", The Wilson Bulletin, vol. 94, no. 2, pp. 206-208.

 

Lek mating systems in birds - a model for studying sexual selection.

Bradbury and Gibson (1983) described leks as ‘assemblies of adult males which females visit solely for the purpose of copulation’. Males of lek-breeding species provide only genetic material to resulting offspring, interacting with females only during mating (DuVal & Kempenaers 2008, Pruett-Jones & Pruett-Jones 1990). Lek mating systems have long been used to study sexual selection, as lekking species are known for extraordinary sexual dimorphism in ornamentation, plumage colour and size (Hess et al. 2012). Mating success among displaying males is generally highly skewed, with few males often responsible for the majority of matings (DuVal & Kempenaers 2008). There has been much discussion as to whether male-male competition or female choosiness is the primary driver of this behaviour and subsequent variance in male mating success (Pruett-Jones & Pruett-Jones 1990).

In some species of Birds of Paradise such as the Greater Bird of Paradise (Paradisaea apoda), males form leks in which they perform their communal courtship displays https://www.youtube.com/watch?v=KIYkpwyKEhY. Viewed on 3rd May 2017. 

Lance-tailed Manakins (Chiroxiphia lanceolata) form leks that consist of alpha males, each of which are assisted in their display by beta helpers that do not mate with any of the females attracted by their display (DuVal & Kempenaers 2008). Research has shown that both inter- and intrasexual selection occur within this species in distinct episodes, with male-male competition occurring to obtain alpha status and female mate choice occurring among displaying alpha males (DuVal & Kempenaers 2008). Nearly all chicks are sired by lekking alpha males, however the way females choose which alpha male or males to mate with is still yet to be determined - they may employ a compatability criterion, selecting for good genes and genetic compatibility or their choice may be random and determined purely by the placement of males and their accessibility (DuVal & Kempenaers 2008, Neff & Pitcher 2005). 

Male Lance-tailed Manakins (Chiroxiphia lanceolata) performing a courtship display. One is an alpha male the other a beta male assisting in the performance. Only the alpha male gets to mate with an impressed female. Are the beta males doing this to learn the right moves for if or when they gain alpha status??? https://www.youtube.com/watch?v=cAwevkUaB2Q. Viewed on 3rd May 2017.

I have found quite a lot of conflicting information regarding the factors influencing the formation of leks and the highly variable success rates within the males of the lekking species. This has once again highlighted how little we still know about bird behaviour. Each species of bird has apparently evolved its own unique mating system, and while it is sometimes possible to find similarities between these mating systems, drawing conclusions that attempt to describe all mating systems, or even one mating system, often results in unneeded controversy!!! There is plenty of variation within one mating system such as lekking, so the variation between mating systems is mind-boggling. Whether a mating system is more influenced by inter- or intrasexual selection is often extremely hard to determine and as we see in the Lance-tailed Manakin (Chiroxiphia lanceolata)  the two are often inextricably linked.


References

Bradbury, J.W. & Gibson, R.M. 1983. "Leks and mate choice", in P.Bateson (ed.), Mate choice, Cambridge University Press, Cambridge, pp.109-138.

DuVal, E.H. & Kempenaers, B. 2008, "Sexual selection in a lekking bird: the relative opportunity for selection by female choice and male competition", Proceedings of the Royal Society B: Biological Sciences, vol. 275, no. 1646, pp. 1995-2003. 

Hess, B.D., Dunn, P.O. & Whittingham, L.A. 2012, "Females choose multiple mates in the lekking Greater Prairie-Chicken (Tympanuchus cupido)", The Auk, vol. 129, no. 1, pp. 133-139.

Neff, B.D. & Pitcher, T.E. 2005, "Genetic quality and sexual selection: an integrated framework for good genes and compatible genes", Molecular Ecology, vol. 14, no. 1, pp. 19-38. 

Pruett-Jones, S.G. & Pruett-Jones, M.A. 1990, "Sexual selection through female choice in Lawes' Parotia, a lek-mating Bird of Paradise", Evolution, vol. 44, no. 3, pp. 486-501.