"their natural habitat which is mostly urban in my research"

by the way, how natural is that urban habitat?

Free ranging dogs are present mostly in the developing countries. They are omnipresent in habitats like urban, suburban and rural areas. For my research, I am considering dogs of urban areas. They do not come under direct human supervision but heavily depend on human provisioned food. 

Start having a look at this excellent review to identify potential key factors: 

http://imedea.uib-csic.es/bc/gep/docs/pdfsgrupo/articulos/2013/OroetalECLET2013.pdf

Then you might even think about designing an experiment to test scavanging efficiency. I am not sure whether this has ever been done in urban habitats but there are published cases regarding other habitats, e.g. :

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449174/

I hope this helps, best luck with this. 

Danilo

The Oro et al 2013 paper is a great place to start to look broadly at anthropogenic food types. You may also want to look through other primary papers in this area of work for how they quantify foraging and/or resource availability. Perhaps one first pass would be to do 1) behavioral observations of foraging and/or 2) fecal/stomach content analyses for prey types. The (top) items identified could guide a more systematic approach to quantifying food availability. Perhaps something like "food transects" through your study sites? I've seen other studies use household surveys to complement the scat/stomach analyses. For literature, the urban fox work in Europe is a good place to start:

http://www.sciencedirect.com/science/article/pii/S161650470470107X

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2007.01257.x/full