Bird excreta is a nasty mix of faeces and urine. It’s not the best combination to land on your tent but it is easily removed by brushing off when dry or gently washing away with mild ph-neutral soapy water before swilling well. A good proprietary tent cleaner, like Outwell Clean Guard, can also be brought into play but rarely necessary. Reproof? Only if that soap has stripped off the external Durable Water Repellent (DWR) finish - again, rare with ph-neutral soap but a detergent will. If needed, just respray with Outwell Water Guard or similar.
However, the real pain is tree sap. This tends to fall into two categories: that awful conifer resin that smells delightful yet spreads mayhem like napalm, and a sticky substance often mistaken for tree sap – the aphid’s wax-based defensive honeydew much loved by ants.
The latter creates a splattering effect of tacky dirty rain that looks a disaster. But you’ll often find it easily washes off if treated like bird mess. Heavy rain can also clean it away. Resin is more serious.
Resin becomes a sticky mess if heated by the sun. The temptation is to scrape the worse away using something like the edge of a credit card but this can spread the problem. You could leave to dry before trying to crack it off but by then it will be hard to separate from the outer’s fibres.
Of course, if left to deal with when you get home the chances are, unless liberally sprinkled with talc, it will adhere to any part of the tent with which it comes into contact. Remember, it gets stickier and more liquid the warmer it is – and think how hot your car gets when left in the sun while you grab a bite to eat on the trip home.