Ground feeding birds under the realm of opportunists
Woke up in the morning listening to bird chirps, chuckles, gurgles and coos.Lying on the bed I fancied our Hibiscus tree studded with birds of blue, red, yellow, white and so on. After couple of minutes,finally making up my mind,picked myself up to reach the balcony and to my surprise, and slight disappointment, all I could see is a tree of noisy bunch of purplish brown birds, the Common Mynah1. The incident, though it wasn’t possible then to perceive ample scale of the phenomenon- phenomenon of Common Mynahs taking over other ground feeding birds, stayed on me as an image, a notion.
|The Common Mynah|
‘Isn’t this the way nature goes about? Why should nature’s way of better species replacing weaker ones gain any importance scientifically?’ One might ask. The answer would be an ‘yes’, I must concur, but the emphasis here is on the fact that whatever prevails should be a better species, which is not the condition in the phenomenon we look upon here. Mynahs are clearly not better species, in terms of feeding adaptations, preying skills or survival adaptations like agile flight, camouflage,swiftness on land, than most of the species it is likely to replace.
It might sound paradoxical to declare a dominating species as weaker one in terms of evolutionary adaptations, but it must be understood, however, that all the adaptations above mentioned, that Mynahs seem incompetent in,are individual. Social adaptations of Mynahs afford an explanation for the phenomenon. Mynahs are highly social birds strutting haughtily in quarrelsome pairs often forming foraging groups ten to twenty strong. Before discussing Mynahs’ social adaptations and its evolutionary upshots, let’s look into the incentives behind any animal(including birds) being social.
Food and its distribution along with habitat of any animal, in effect, design their social pattern.As mentioned before animal’s social patterns, like being solitary, in pair, or groups of different sizes, is determined predominantly by their food and its distribution2. When the food is nutritious and bulky the animal need not spent much time feeding hence it is not vulnerable most of the time and can afford to be solitary, as they can watch out for themselves from their predators e.g. king fisher, weasel. For animals on top of the food chain vulnerability is not a concern, although it might have to defend its kill from other predators, here hunting technique contributes in deciding the social pattern3. This category does not include scavengers with, excepting the fact that it’s just putrid remains, similar food design. These animals work in groups to save energy spent in search of carcass through vast area.
When the food is less nutritious the animal needs to spend much of its time feeding making it vulnerable hence they tend to form social groups so that they have more watchful eyes, this would also mean more mouths feeding, giving raise to social hierarchy, severity of which depends on the availability of food. Animals like sparrows, spotted deer, to name a few, fall under this category.Animals with rich cultural knowledge, for better survival, are bound to be social in two ways. One, their offspring inherit very less instincts, as they might act against cultural knowledge, and their growth period is prolonged so as to accommodate much learning, making them very vulnerable. Two pairs of watchful eyes often aren’t enough protect them, most of the primates for example. The other reason would be more individuals in a group would mean more exposure,therefore learning takes place faster.
|A Spotted Dove, one of the victim belonging to second category|
Those animals feeding on nutritious food available in small packages, groups of small sizes, preferably pairs are favoured. This enables them to share information either of food sources are of threats without much competition on food. These animals feed shorter time span than those of above category at the same time longer than those of the first category. Their alertness, therefore, is somewhere between that, which explain their social adaptations. Sunbirds and lorises would be best examples.
|A Magpie Robin, one of the victims belonging to third category|
Mynahs, peculiarly, have a diet which includes both of the last two categories i.e. they feed on both less nutritious food and small packed nutritious food. This makes up their specific social structure of having feeding pair welcome (really?) to form occasional foraging groups. Mynah’s natural diet ranges as invertebrates, fruits, nectar, grain and human garbage. This wide range of food habits prevented them from any possibility of specializing. They are designed to be opportunistic feeders and therefore, not surprisingly, supposed to be in large numbers, as they have always been (can be seen in the diagram). For such a widespread bird (more widespread than House Crow) found in such numbers any unusual favourable condition would result in drastic insurgence of population. This is where human garbage comes in.
|An ideal population circle|
Human garbage is an interesting combination of food source. It is a sea of less nutritious food dotted with bonus of nutritious food both in small packages and large chunks. Excepting bulky nutritious food, which House Crows4dominate, the rest forms a perfect menu for Mynahs. Mynah’s volatile social structure further supported them conquer this food resource. Thus what had previously been amateur opportunists then evolved to be garbage specialists. They eventually habituated human presence5, and, in fact, turned bold and aggressive. Thus human garbage, more than any, formed Mynah’s primary food, and with its consistent escalation has comforted huge population of the bird.
|Mynahs with Rock Pigeons|
This might seem perfect that, increase in food source naturally increasing the population of the consumer, therefore striking a natural balance. But the trouble arises from the fact that Mynahs are of persevering nature that they refuse to give up their other food habits. Thus it essentially comes out to be these bold, aggressive, confiding, social birds opposed, to comparatively less so, other birds. It is much in favour of Mynahs, but nevertheless the situation is completely man-made, that way what are basically just two selective forces (adaptability to human garbage and his presence) overcome all the natural selective pressures, which moulded other specialised birds, to favour Mynahs.
The situation is made further hostile to these specialised birds due to man-made fluctuation6 in their natural diet like nectar, grains, fruits, and invertebrates. Being specialised they cannot rely on any other back up food source whereas Mynah population is buffered by constant human garbage outputs. This phenomenon is more severe in urban environment with more human caused primary food source instability, his presence and garbage output. This phenomenon also affect some birds indirectly, for example; Cuckoos are basically canopy feeders and not competed by Mynahs directly but they brood-parasite Babblers and other small birds like Prinias which in turn suffer the phenomenon. Mynahs roost communally making them less vulnerable to their possible predators.
|After human Interference|
All the birds depicted in the diagrams are common birds none rare or endangered. Notice the bigger food circle of Mynah and more overlapping. With more overlapping and selective pressures the food circles of other birds would eventually shrink.
As it is obvious now that the phenomenon is not natural let’s look at the consequences. It is mentioned at the beginning that Mynahs are not better species in terms of individual evolutionary adaptations. Their social adaptations come at the expense of their lack of specialisation. They, therefore, can be better survivors but not better feeders. They can never be an apt substitute of those specialised birds they are likely to replace from the food chain for example; Mynahs cannot prey on dry leaf floor dwelling insects as effectively as a Jungle Babbler. They dominate food web at the same time weaken its links.
|Mynahs waiting for a Brahminy kite’s kill, a peculiar behaviour|
Such a system can fall into ecological imbalance in at least two ways. Any depletion in human garbage or human activity directly affecting Mynah population, say a toxic breach in garbage output, would result in ecological imbalance which would have been prevented provided more specialised bird population i.e. when very conditions that favoured Mynahs turn unfavourable their population drastically falls leaving a gap which cannot be filled by other birds7 (as the diagram below illustrates) given the short time scale of the phenomenon.
This gap left behind would result in complete collapse with an upsurge in invertebrate population, failure of pollination in certain species, uncontrolled burst in grass population etc. The cause might seem less likely in this case but in a man-made environment any such possibility can be anticipated and therefore should not be neglected.
The second possibility is a more likely one. The food itself might evolve to be resistive, like developing an unpalatable husk in case of grain or distasteful chemical in the case of invertebrate, rendering it inaccessible to Mynahs. Mynahs cannot specialise to gain access to themas they rely on garbage as their primary food source, at the same time their population, social pattern and confiding nature would still be a threat to specialised or rather able-to-specialise birds. Moreover for bird with such wide range of food habit, loss of access to a few species may not be significant. The result would be similar to the former case though not to that extent.
Given the extent of the phenomenon, one gets a mixed feeling seeing a Mynah. Should they be seen as a bullying pest of bird kingdom? Or as a human being, Should one identify with them as funny walking creatures representing man’s destructive power in bird kingdom?
A friend knowing my interest in bird watching invited me to his place, some time back. I went there without much anticipation and it proved right again. I had a hard time explaining him that it’s just one species, Common Mynah communally roosting. There are not many species out there as it sounds like, I cried out.
1. It’s been six years since the incident and that was much before interest for bird watching grew on me. I now know that Common Mynahs are highly vocal, capable of producing wide range sounds ranging from chattering, chirping, whistling, to occasional mimicry.
2. Food and its distribution, though are most important deciding factor, do not account for social behaviour solely. Sensory capabilities, energy efficiency, birth rate along with many other factors play a synergistic effect in deciding social pattern of an animal.
3. A Tiger can be solitary because it can sneak up to its prey closer than a savannah inhabiting lion would using much denser vegetation as a cover and can score a large kill, most of the time, with a single pounce. Whereas lions have lesser cover, and their prey is quite large requiring great muscular power to bring down, this comes at the expense of speed hence they need to hunt in pack.
4. The adaptation of house crow to human garbage is another worrying phenomenon. Crows are inveterate robbers of bird nests, as their population increases with increasing garbage output
other birds might suffer severe mortality rates.
5. Human garbage has been in to existence long enough for Mynahs to have evolved their confiding, inquisitive nature and gradually getting habituated to human presence.
6. This phenomenon is much seen in aquatic environment, as the fluctuations in aquatic life increases more specialised aquatic birds like Ibises and open-billed storks are dominated by opportunistic feeders like Cattle Egrets.
7. Birth rates are limited to generations and therefore often fail to cope up with sudden increase in death rates.
I thank Thamarai.s.Elanthirayan my friend and an aspiring photographer for the pictures presented.
1.A photographic guide to birds of India-Bikram Grewal, Bill Harvey and Otto Pfister, Princeton University press,2002 periplus editions
By coincidence all my three articles so far are about one thing dominating over others. This article is inspired by the trivia that I recently read about Common Mynah being declared as one of the most invasive species. When I further read up I found some of the species it is said to threaten as an invasive species are found in India too. The article, though lacks any statistical data to back up and is solely based on observations, is presented with the confidence that arguments put forth here are substantial and defendable. I would be glad, therefore, to have my arguments discussed or to have data defying or supporting the arguments than being criticised for its lack of statistical data.
Some local Tamil names
Mynah-ur kuruvi or naganavai
Spotted Dove- mani pura
Rock Pegions-mada pura
Wagtails,Pippits- vaalaatti kuruvi