Wildlife Institute of India

There was a time, not so long ago, when most zoo directors came up through the ranks within the institution. These were often biologists or veterinarians who held various roles until they eventually rose to director after many years of service and leadership. To be sure, many current (and probably future) zoo directors took this route. However the times are changing.
Managing a zoo is an increasingly complex undertaking. Beyond overseeing a staff of hundreds, zoo directors are also tasked with leading international conservation efforts, overseeing enormous budgets and varied revenue streams (i.e. tickets, concessions, membership, gifts, events, municipal contributions, etc.) and launching multimillion dollar fundraising campaigns to build modern exhibits. They also have to manage a diverse group of stakeholders, including members, local government, conservationists, activists, donors (both corporate and individual) and their own employees. Just because you love animals, doesn't mean you'll love multiple weekly finance meetings about your zoo's operating budget :) Consequently many zoos and zoo boards are now looking for leaders with substantial general management experience in addition to a clear passion for and commitment to animal welfare and conservation.
Long story short, working your way up through a zoo is a fine option but so is building your leadership skills in a corporate or large non-profit environment. Just make sure you continue to learn about and contribute to the zoo world while you develop professionally elsewhere.
Finally if you truly want to be a zoo director, and this goes for many other zoo professions as well, be prepared to move wherever there is an opening. There are about 230 zoos and aquariums accredited by the Association of Zoos and Aquariums (AZA) in North America and most of these are not in major cities (think the opposite). Zoo directors often stay in their roles for many, many years so openings are limited. Many zoo directors in major cities were offered the role after doing an outstanding job at a smaller zoo somewhere relatively remote.

The Wildlife Institute of India, Dehradun is one of the premier institutes in wildlife conservation, offers M.Sc in wildlife research and management. Graduates in science, agriculture, forestry, veterinary and life sciences are only deemed eligible. The eligible candidates have to take National Entrance Test (NET) at one of the 6 centres (Bengaluru, Dehradun, Kolkata, Mumbai, Delhi, and Guwahati). The NET which is of 2.5 hours, tests the candidates on GK, general science, life sciences, forestry, agriculture science, veterinary science, geology, geography, sociology, economics, and engineering. Shortlisted meritorious candidates based on NET screening will be called to take a personality and aptitude test (PAT).
The National Centre for Biological Sciences is another premier institute in wildlife conservation. It offers M.Sc in wildlife biology and conservation for graduates in any discipline. This course is offered once in every two years. The course is in collaboration with the Centre for Wildlife Studies (CWS), Bengaluru and Wild Life Conservation Society, (WCS-New York) the degree is offered by Tata Institute of Fundamental Research. The selection is through national-level written test and interview. Along with the written test, a detailed application, reference letters and an interview of short-listed candidates are also required. The written test assesses general knowledge, English language skills, analytical and quantitative abilities and knowledge of basic biology, ecology, and conservation issues.
Other institutes:
Amity Institute of Wildlife Sciences offers M.Sc in wildlife sciences and Saurashtra University, Rajkot, Gujarat offers M.Sc in wildlife sciences.

Eligible candidates will be required to appear for a written NET in any one of the centres Bengaluru, Dehradun, Kolkata, Mumbai, Delhi and Guwahati.
The NET will be for 2.5 hours
The test will have 30 marks multiple choice questions on General Awareness including Current affairs, Quantitative Skills, Geology, Geography, Sociology, Economics and Engineering
40 marks multiple choice questions in wildlife sciences including natural history, biogeography, ecology, genetics, vegetation science, population ecology, habitat ecology, behavioural ecology, conservation biology, wildlife health
30 marks essay questions covering conservation issues
Shortlisted meritorious candidates based on NET screening will be called to take a personality and aptitude test (PAT) at Dehradun
Final selection to the course will be made on the basis of combined merit of 50% marks obtained in the Bachelor's degree and 50% of PAT.
You can procure books for the NET exam online on any of the popular websites like Amazon or Flipkart.
1) UGC NET Paper-1 Previous Years Solved Papers: 26 Papers of Last 13 Years (2004-2017) Kindle Edition by Dr. Veenu Saini (Author).
2) CBSE UGC-NET: Teaching and Research Aptitude-JRF and Assistant Professor Exam Guide (for Paper-I) by Dr. M S Ansari & RPH Editorial Board (Author).