Dominate "Hands" for Birds

Do Birds Have a Dominate “Hand”?

Ollie J. - September 15, 2018

Figure 1 Mean (±s.e.) hand and eye preferences for 16 species of Australian parrots. The regression line illustrated (r2 = 0.99) was calculated based on the exclusion of a single outlier. (Figure and caption from [7])

Figure 1- from [7]

An experiment was done by Dr. Culum Brown, 322 Australian parrots from 16 species where observed. In this study posted to Biology Letters [7], the objective for these birds was simple: pick up an object with one of their feet. In this study almost all of these birds showed a strong preference to one foot. In most species, their preference of which hand to use varied

depending on the individual, such as how roughly 90% of humans are right-handed and 10% of humans are left-handed [6]. However, in 4 of the 16 species the preference of a foot remained the same through the entire species. Dr. brown told BBC news that he was “yet to find a right handed Sulphur-crested cockatoo” [5].

In his experiment, Dr. Brown concluded that roughly 47% of birds are left-handed and 33% of birds are right-handed, with the remaining birds ambidextrous [4]. The only species found that was 100% was the cockatiel [5]. The outlier seen in Figure 1 was the cockatiel, who was the only species in which no bird had a dominant hand.

The Science Behind It

So why do birds have strong hand preferences, and why are cocktails an exception? Well, in humans our handedness comes from the lateralization of our brain, or use of one hemisphere. This turns out to be true for birds as well [4]. This lateralization effects the birds whole body however. Because birds’ eyes are on the side of their head, they cock their head to one side to get a better view of the object in question. Left-handed birds always cock their head to the right, and right-handed birds always cock their head to the right. This is most likely the effect of the birds hand-eye coordination. In a left-handed bird who cocks their head to the left for a better view of an object, they will use their left foot to grab it because their left eye will be able to track it easier [2].

Cockatiels do not have this hand-eye coordination due to the fact of how their forging has evolved. Cockatiels have evolved to forage in the grasslands of Australia, which involves little no no hand-eye coordination [5].

Can This Be an Advantage to Dense Flocks?

This almost 50/50 split mentioned in Dr. Brown’s study may even help birds. In a different test the neuroscientist from the university of Queensland, Mandyam Srinivasas, tested budgie flight paths. Budgies, or Budgerigars, are a small type of parrot species in the parakeet family. They travel in dense flocks through Australia. When presenting the budgies with an obstacle uncentered in a hallway, all 5 budgies chose to fly to the side with the biggest opening. However, when the object was centered 4/5 budgies had a clear preference over what side to fly to [1]. A separate test proves that budgies also have a strong preference over what side to perch on. All the tests show that 50% of budgies choose the right, and 50% choose the left [1]. This 50/50 spilt means that when faced with an obstacle in the wild, the dense flock of budgies will split in half around the object. This will help the flock not

"Whilst landing on a tree, for example, it would be important to find a clear path" says Srinivasas, "as well as avoid collisions with other birds."

My Own Study

Amazed by the fact that birds have a dominate “hand” or side like humans, I decided to use this information to test my own Severe Macaw named Casper. My interest in this study when I noticed Casper’s left foot was colored orange (which always happens after he eats orange pepper), but his right foot was completely clean. I came to the conclusion that he only used his left foot to eat peppers that day, seeing as he doesn’t usually clean only one foot. I decided that it probably doesn’t mean anything, until I started researching.

After observing Casper for a few days I noticed that every time I saw him eat, he grabbed his food with his left hand. Every time he scratched himself, he used his left hand. Every time he flew to me, he went to my left shoulder even though both shoulders where completely acceptable landing spots. This led me to the conclusion that my Severe Macaw, Casper, is indeed a leftie.

References

[1] I. (2014, March 14). Right- and Left-Handed Birds Help Their Flocks Fly Better - Inkfish. Retrieved from http://blogs.discovermagazine.com/inkfish/2014/03/14/birds-that-are-right-or-left-handed-help-their-flocks-fly-better/

[2] ReardonFeb, S. (2017, December 10). ScienceShot: Human Handedness Is for the Birds. Retrieved from http://www.sciencemag.org/news/2011/02/scienceshot-human-handedness-birds

[3] Dominant foot...is my bird left or right handed? (n.d.). Retrieved from http://www.mytoos.com/forum/ubbthreads.php?ubb=showflat&Number=257739

[4] Parrots tend to be "left handed," study finds. (2011, February 03). Retrieved from https://www.reuters.com/article/us-parrots-hands/parrots-tend-to-be-left-handed-study-finds-idUSTRE71277420110203

[5] Brennand, E. (2011, February 02). Earth News - Parrots prefer 'left handedness'. Retrieved from http://news.bbc.co.uk/earth/hi/earth_news/newsid_9382000/9382181.stm

[6] Why are more people right-handed? (n.d.). Retrieved from https://www.scientificamerican.com/article/why-are-more-people-right/

[7] Brown, C., & Magat, M. (2011, August 23). Cerebral lateralization determines hand preferences in Australian parrots. Retrieved from http://rsbl.royalsocietypublishing.org/content/7/4/496