In my opinion, they won't be able to track your income unless declared. Cause if Bitcoin is a system that can be tracked by centralized authorities like banks and government, where's the sense of it being decentralized.
They can track using the bank details, because banks may be asked to provide details if account is being open for btc transactions or any suspicious transactions happening regularly than those details will be forwarded to them and then you will be under scanner.
If you are using an offshore bank account, then the chances are quite low (unless the amount is very big). There are protocols in place to get information from foreign banks and it is quite complicated. The authorities are not going to use this route, unless the amount is quite large.
Now every bank is tracing the bitcoin transactions because many people are exchanging their bitcoins in a local exchange into their fiat currency. It is very easy for banks to easily identify those transactions.