In this series of articles, I will introduce the reader to the scienceof ethology, somewhat indirectly by describing simpleexperiments, both old and new, designed to understand howand why animals behave the way they do. My emphasis willbe on the design of the experiments and my goal will be tomotivate readers not only to think about the design but alsoto come up with alternatives and improvements. Motivatedreaders can indeed replicate some of these experiments evenif they end up replacing the study animal or the behaviours ofinterest with their own favourite choices. In the first part ofthe series, I describe how Niko Tinbergen – Nobel Laureateand one of the founding fathers of ethology (the science of animalbehaviour) – designed remarkably simple experimentsto successfully understand how digger wasps find their ownnests in a complex habitat also consisting nests built by otherwasps.

In the second article in the series, I will describe how theyoung Karl von Frisch, later to become another founding fatherof ethology and Nobel Laureate, defied established authorityto design simple yet logically clever experiments toshow that honey bees indeed have colour vision. His experimentsforever changed our view of animals and also the wayexperiments in animal behaviour are designed. It might interestreaders to know that Karl von Frisch’s experimentsdescribed in this part inspired Tinbergen’s experiments describedin the previous article in this series.

In this article, I will describe how a simple, curiosity-basedexperiment to understand how ants are smart enough to choosethe shortest path led the exploration of self-organization andswarm-intelligence and resulted in major applications in computerscience and optimization algorithms. The focus willbe on curiosity, simplicity, interdisciplinarity, and being unmindfulof immediate applications.

This article describes simple experiments that showthat honeybees estimate the distance they have flown, by means of ‘opticflow’, i.e., the extent of image motion experienced by theireyes. The estimated distance is then communicated to thebees at home through the tempo of their dance (number ofdance circuits in 15 s) or the duration of the waggle phase ineach circuit. The experiments also provide strong evidenceagainst the previously held view that distance is estimatedby the amount of energy consumed during the flight. Theseexperiments illustrate how cutting-edge research is possiblewith little or no facilities, equipment or money, by asking theright questions, optimizing the design of the experiments andregarding previously fashionable theories with an appropriatedegree of scepticism.

In this article, I will describe experiments designed to understand how ants estimate the distance they have walked. They rival in their simplicity, the experiments described in my previous article, designed to understand how bees estimate the distance flown. Although ants can also use optic flow to estimate distance, in the absence of optic flow cues and of pheromone/chemical trails, as may sometimes be the case in the desert ants, \emph{Cataglyphis}, ants estimate the distance walked, not by the energy expended but, believe it or not, by `counting' (or integrating) the number of steps they have taken. This was proved by showing that ants on stilts (elongated legs) overshot the required distance to return home while ants on stumps (shortened legs) undershot the required distance.

In this article, we move from sensory physiology to psychologyand consider the proverbially lazy drone. I will describehow some simple experiments permitted us to understandwhy males in the Indian paper wasp Ropalidia marginata dono work in the colony even during the time they live in it. Takingthe behaviour of feeding larvae as an example of work,we show that male wasps normally do not feed larvae, not becausethey are incapable of doing so, but because they do nothave access to enough food and also because female wasps areso much better at this job. As a confirmation of this conclusion,we could cure the males of their laziness, i.e., get themto feed the larvae by providing them with excess food andleaving them in the presence of hungry larvae, without thepresence of females.

In this, and the next few articles, we will continue to explorethe social biology of the primitively eusocial wasp Ropalidiamarginata through simple experiments. Since eachwasp colonyhas a single fertile queen and several sterile workers, andsince all or most wasps are capable of taking on both roles,the wasps have to decide who will be the queen and who willbe the worker/s. Such a decision has to be made both whennew colonies are being initiated as well as when an old queenin a mature colony has to be replaced by a new one. Here, Iwill describe a simple laboratory experiment that reveals thatin the context of new nest initiation, wasps decide who will bethe queen by fighting—the winner becomes the queen and theloser/s become the worker/s. The same experiment, in additionto revealing the proximate mechanism of the division ofreproductive and non-reproductive labour, also throws lighton the advantages of such division of labour.

Continuing to explore the fascinating world of the Indian paperwasp Ropalidia marginata, in this article, we will ask howwasps choose their queens in another context. In the previousarticle in this series, we saw how a simple experiment revealedthat wasps fight, i.e., indulge in dominance-subordinateinteractions, and the winner becomes the queen and theloser becomes the worker. This was in the context of newnest foundation. But contextmatters. When the same waspsonce again have to decide who will be their next queenif the first one dies or is experimentally removed, the samerules do not hold. The wasps in a mature colony continueto show dominance-subordinate interactions and can even bearranged in a dominance hierarchy, but the dominance ranksof the wasps do not predict who their next queen will be.How they choose their next queen in this context continuesto be an enduring mystery. In this article, I will describe foursimple experiments that have helped us come close to nailingthe culprit, although I must confess that we have not yetfound the smoking gun—the chase is on, and we are hot onthe trail—please join in!

Continuing to explore the intriguing world of the Indian paperwasp Ropalidia marginata, here we will focus on their fighting behaviour. When wasps fight, there is, as expected, a winner and a loser. The winner is said to have shown dominance behaviour, and the loser is said to have shown subordinate behaviour. What is the function of such dominance subordinate behaviour? We saw in the 7th article in this series [1] that in the context of founding new nests, wasps fight to decide who would be the queen and who would be the worker. We then saw in the 8th article in this series [2] thatwhen wasps have to decide who would be their next queenin a mature colony, they do not decide by fighting, although they fight for other reasons. We will see in this article that workers continue to show dominance-subordinate behaviour in mature colonies. What is the function of this aggression displayed by the workers? In this article, I will describe two simple experiments that help us answer this question, and show that the function of wasp aggression can be quite different in different contexts.

Continuing to explore the intriguing world of the Indian paperwasp Ropalidia marginata for one last time, here we willfocus on the function of fighting behaviour in two additionalcontexts (i) the hyper-aggression of the potential queen duringqueen succession and (ii) during encounters with nonnestmatewasps. We will see again that the function of fightingis different in different contexts. We have already seentwo different functions of fighting in two different contexts—to decide who will be the queen and who will be the workerin the context of founding new nests, and to regulate foragingin mature colonies by conveying colony hunger levels toforagers. Here we will see that the function of the potentialqueen’s hyper-aggression is to boost her own ovarian developmentand the function of aggression towards non-nestmates isto keep them away, and if necessary, to kill! As before, ourprimary focus will be on how to design simple experimentsthat will help answer a direct question, while minimising theneed for expensive equipment or other facilities.

Charles Darwin proposed a separate theory of sexual selec-tion, as distinct from his theory of natural selection, to ac-count for adaptations that confer success in finding a mate, which may sometimes be quite the opposite of what is best for survival. Darwin’s proposal that females have a sense of beauty and choose mating partners that appear beautiful to them was met with much scepticism. But today we have a rather detailed understanding of what animals find beauti-ful and why. In this article, I will describe a few very sim-ple experiments performed by Michael J. Ryan, in collabora-tion with A. Stanley Rand, herpetologist extraordinaire and Merlin D Tuttle of the Bat Conservation International fame, that laid the foundation for our current understanding of the meaning and evolution of beauty. Studying the t´ungara frog on Barro Colorado Island, a research station of the Smithso-nian Tropical Research Institute in Panama, they showed that (1) male t´ungara frogs can produce both simple calls, consist-ing of just a whine, or complex calls in which one or more chucks are added to the whine, (2) female t´ungara frogs have a decided preference to mate with males giving complex calls,(3) males are nevertheless reluctant to add chucks to their calls and generally do so only when they hear other males calling, and (4) the local predatory fringe-lipped bat also has a decided preference to eat males giving complex calls. Male t´ungara frogs thus face a trade-off between sex and survival. These experiments not only answered the question of why males don’t do their best when it comes to singing, but they also set the stage for many more sophisticated investigations that have led to an understanding of how and why natural selection has favoured this particular sexual aesthetic in the frogs and this particular culinary aesthetic in the bats.

There are many examples of perfectly palatable animals re-sembling related unpalatable species and, thereby, avoiding attack by predators who have learnt or evolved to avoid the unpalatable species. To facilitate recognition by predators, unpalatable species often have warning colourations, which is what is mimicked by the palatable species. This form of mimicry is known as Batesian mimicry. While there are many well-documented examples of Batesian mimicry among butterflies and other arthropods, there are somewhat fewer examples amongst vertebrates, and even these examples are of-ten debated. The coral snake mimicry system in North America, where non-venomous kingsnakes and milksnakes mimic venomous coral snakes, is one of the best-studied vertebrate examples of Batesian mimicry. However, it has also been debated for over a century. In this article, I will describe three experiments using plasticine replicas of the mimics designed to understand the effectiveness of their mimicry. These field experiments were performed in the natural habitats of the mimics, the models and their predators, by David W. Pfennig and his students and collaborators, in the states of Florida, North Carolina, South Carolina, and Arizona in the USA. The simple, clever, and low-cost experiments have significantly strengthened the hypothesis of Batesian mimicry in this system. They have also provided an unexpected new understanding of how mimics might evolve from cryptic ancestors through a process of gradual natural selection.

That the cuckoo lays its eggs in the nests of other species and does not build its own nest or raise its own offspring, is one of the oldest known facts about Natural History and has been abundantly and eloquently immortalised in myths and stories, art and literature, music and poetry, philosophy and morals. Attempts to understand this curious phenomenon in any rational way began just about 100 years ago. With a landmark study consisting of a few simple and elegant experiments that needed no laboratory or funding, Nick Davies and Michael Brooke at Cambridge University in the UK ushered in its modern scientific study as recently as 1988. In this article, I will describe their experiments and their results and conclusions, accompanied by a running commentary relating their work to the theme of this series and end with some more general reflections on the pursuit of the science of animal behavior.

I have had multiple aims in writing this series of articles. My primary aim has been to show how simple and innovative experiments can be performed at almost no cost, by nearly anyone, to create significant new knowledge. The history of science shows that this is true in most areas of scientific research, albeit to varying degrees. I have focussed on the field of animal behaviour both because I am more familiar with this field than others, but also because, the field of animal behaviour is especially well-suited for such low-cost research. It has also been my aim, of course, to discuss the princi-ples of ethology (the scientific study of animal behaviour), through the medium of these experiments. My motivation in writing this series is to bring social prestige to low-cost research, make the practice of science more inclusive and democratic, and empower large numbers of people to become knowledge producers rather than merely remain knowledge consumers. The people I especially have in mind are, less-endowed sections of society, including, but not restricted to, under developed countries, marginalised institutions and individuals, students, the general public, amateurs, and all those with little or no access to large research grants and sophisti-cated laboratory facilities, for whatever reason.Note: Some passages in this article are reprinted from Suggested Readings [4, 5, 15 and 16].