Why do Muslims of Karnataka have their mother tongue as Urdu unlike those Muslims in Kerala and Tamilnadu where they speak respective native languages(Malayalam & Tamil)?

Many places in Karnataka like Bidar, Gulbarga, Bijapur were ruled by Nizam of Hyderabad until 1948 and Urdu was the official language of Nizam. And places like Raichur (bordering Rayalaseema in Andhra Pradesh) and to an extent, Bangalore and Mysore had Muslim rulers in the past. Bangalore/Mysore had rulers like Tipu Sultan/Hyder Ali and Rayalaseema had many Muslim rulers who were feudal lords and subordinates to Nizam of Hyderabad. Hence, the general Muslim population in these areas tend to use Urdu for everyday communication. Large parts of Kerala and Tamil Nadu were under British rule or Indian kings (Cochin/Travancore). Here, most of the Muslim population adopted the local language (same with British-ruled coastal Andhra) and they are fluent in vernacular languages. There were Muslim-ruled areas in Tamil Nadu like Arcot, but given the strong pro-Tamil/anti-Hindi movements in Tamil Nadu, it was advantageous for Muslims there to become fluent in the local language, even more than the Muslims in coastal Andhra or Kerala. An interesting case is that of coastal Karnataka, where there are whole towns where descendants of Arab traders and other trading communites (http://en.wikipedia.org/wiki/Nawayath) live (e.g. http://en.wikipedia.org/wiki/Bhatkal). They use Urdu (mixed with other languages) for everyday communication.

The Muslims of TN and Karnataka are mostly of North Indian Origin and they tend to use Urdu more.In Kerala, Muslims are mostly mappilas ,of Arab origin and they are malayalam speakers.  To the south we can find Tamil Muslims (https://en.wikipedia.org/wiki/Rowther ) who were originally Tamil speakers but have grown out to use Malayalam as their first language.(well thats Malayali nature!).In TN and Karnataka also these Muslims of Tamil origin can be found.And in Mangalore they speak https://en.wikipedia.org/wiki/Beary_dialect  (Thank u Mr. Vikram Hegde)

Language of Muslim communities of South India depends on the origin of that community. If they are descendants of North Indian rulers (Mughals) or the Bahamani Sultanate or their progeny, they speak Hindustani/Dakhani/Urdu. If they are descendants of Arab traders or Yemeni settlers or Arab missionaries they end up speaking some form of local language. Communities set up by various Arab settlers are older and they grew in isolation from Arab lands and ended up adopting local language. Communities set up by the North Indian Muslim expansion are relatively newer and remained connected with Hindustani speakers and could preserve their language.Most Muslim communities of Karnataka can trace their origin to Bahamani Sultanate, especially the Adil Shahis of Bijapur who ruled much of Karnataka after the fall of Vijayanagara. Hence their mother tongue is Hindustani. There are two exceptions to Urdu-speaking Muslims of Karnataka: Nawayat Muslims of Bhatkal speak Konkani and the Beary Muslims of Mangalore speak Beary, with Kannada as the literary language. So much so that Manjeshwar in Kerala traditionally elects a Muslim League MLA who is a Beary who in turn takes his oath in Kannada in the Kerala Assembly. Interestingly, the Nawayat Muslims of Bhatkal speak Konkani but the Muslims of Goa themselves speak Hindustani.Assumption of your question is not correct. All Muslims of Tamilandu do not have Tamil as mother tongue. Vaniyambadi Muslims’ mother tongue is Hindustani. Community established by Nawab of Arcot in Northern Tamilandu is a community of Hindustani speakers, though unlike Karnakata, these Muslims have been heavily Tamilized. Other Muslims of Tamilnadu, Labbay Muslims and Marikkar Muslims (Dr Abdul Kalam) speak only Tamil, and they have Arab rootsNor do all Muslims of Kerala have Malayalam as mother tongue. There is a small minority of Muslims in Kerala who are called Pathan Muslims who speak Hindustani at home. The other Muslims of Kerala: Mapilla, Ossan, Pusalan have Arab roots or are local converts, and speak only Malayalam.

Idk, about the other responses here, but I'll be speaking as a person of Dakhini (Specifically, Hyderabadi and Bangalori) descent (I'm Canadian), and my own research. South India is home to many Muslims, of various ethnic groups, and one such group are the Dakhini Muslims, who are descendants of Semitic peoples, mainly from the Arab peninsula, and to a certain extent even Persian and Turkish merchants and warriors, mixing in with local Dravidian, and even a few Indo Aryan peoples living there. Our culture is heavily influenced on the arrival and spread of Islam in the Indian subcontinent. But the question now is, what about other south Indian Muslims like the Moplah, of Kerala who kept their native south Indian language. Well, after the Delhi Sultanate established itself in the Deccan region (This is why we're Dakhini), the new Dehlavi, or Khadiboli language (Hindustani, now with it's two standardizations Hindi, and Urdu) had reached southern India, and was popular among the Muslim population due to the affinity towards the new rulers based on faith. After the demise of the Delhi sultanate in southern India, a new Bahmani sultanate was born, which became the first independent Muslim kingdom in south India. Now this is where we Dakhinis get our language from, and why we don't speak native south Indian languages like our cousins, namely, the majority of Muslims in Kerala and Tamil Nadu. (Though many people in Chennai are Dakhini). Our culture and language was further developed by the Deccan Sultanates, and the Hyderabad and Mysore Kingdoms. Interestingly enough though, many of us Dakhini people don't even realize who we are, and a sense of identification for us has never been achieved, especially after Indian independence. In fact, most Dakhini speakers don't even care about such an identity, and are looked at as a result of a cosmopolitan India.

I was born and brought up in Bangalore and so were my maternal and paternal grandparents going back 4 generations all lived in Bangalore. The majority of the muslim population in Karnataka have very strong ties to Karnataka have taken up diverse professions generation after generation. It is to the credit of the majority that there was no systematic agenda in marginalizing the minority community and their language and the way its spoken here "dacani urdu" In the past the muslim population have made constant effort to learn Kanada and help enrich culture of Karnataka by adding their own flavor. the extent to which Tipu Sultan, Islamic values and the overall Muslim way of life are discussed in Kanada text books came as a pleasant surprise. However lately with the influx of people from Hindi speaking states into Karnataka and Bangalore in particular, there seems to be a unspoken pressure on the muslim population to use Kanada more often. Most know English, Kanada, Tamil and Urdu very well.

Muslims in Tamil Nadu are overwhelmingly Tamil speakers. They are ethnic Tamils, who mixed with early Muslim traders from Arabia, Persia and Turkey. They themselves traded with South East Asia further mixing with the Malays and have been living in TN for centuries - even before the rest of India came under Islamic rule. Their mother tongue is Tamil and they follow a distinct Tamil culture.Outside TN, there is a considerable presence in Malaysia and Singapore. The population of Muslims in TN is close to 6% of the total population (2011 census). About 4.5 % speak Tamil and the rest speak Urdu/Dakhni (2011 estimated Urdu Speakers in TN).So, about 70 - 75% of the Tamil Nadu Muslims speak Tamil as their Mother Tongue. Tamil Muslim culture/clothing/food habits closely resemble Tamil Hindus, however there is a strong Islamic custom added to it. They can be found all over TN - both urban and rural. Like myself, most of us are fiercely attached to our Tamil Muslim identity and will get offended, if you ask stupid questions like You are a Muslim, but don't speak Urdu? Urdu/Dakhni speakers in TN are mostly recent settlers, who arrived during the Mughal/Deccan Sultanate rule and their culture/clothing/food habits resemble North India. They are mostly found in urban pockets and areas, which were previously under Nawab's rule.

I am a Muslim living in Bangalore and let me enlighten you on this. Firstly, our language is not Urdu. It's actually called Dakhini. The original Urdu is the one spoken in North India and used in Pakistan as an official language. Secondly, we ( most Muslims in Karnataka) people are actually migrants from North India and we migrated centuries ago. Our language changed eventually and became Dakhini. That's why our language sounds quite similar to the original Hindi-Urdu. I am not sure about the Muslims of Tamil Nadu but the Muslims of Kerala are native to Kerala and they therefore speak Malayalam.