Disclaimer: I am not JK Rowling, the characters aren't mine, I don't make any money from this.
(A/N: Somehow, I doubt that AD and MM would have been irresponsible enough to just abandon a baby in the middle of the night - but keeping an eye on him from a less obvious vantage point instead of hanging around immediately in front of no. 4 would make sense.)
Lurking in the luxuriant bushes of no 7's shrubbery, they had a good view of the Dursleys' front step where Harry slept on, motionless. Dumbledore conjured a deckchair with a swift flick of his wand and dropped into it.
"And now we wait" he observed.
"Indeed, Headmaster"
"Are you sure you won't have a sherbet lemon, Minerva? I must confess that it did not occur to me to bring sandwiches."
"Most remiss of you" said McGonagall, dryly. "But I am sure food may be obtained. I shall investigate."
With a quiet rustle of leaves, she vanished deeper into the bushes. Dumbledore, glancing quickly over the road - yes, Harry was still sleeping soundly - settled himself deeper into the deckchair, sucked on a sherbet lemon and hoped that Mrs Dursley was an early riser. She seemed the type, he mused, to be up early both to feel superior and to spy on the neighbours.
Something soft plopped into his lap. Absent-mindedly he scooped it up and felt . . . fur?
"Lumos."
It was a mouse. Quite a large mouse. It was extremely dead, and it appeared to have died of an acute case of cat.
A tabby cat jumped off the garden fence and sat in front of him, tail wrapped neatly round her front paws. She looked decidedly pleased with herself.
Albus Dumbledore tried very hard to ignore the fact that he was holding a dead mouse and glared at the cat.
"Thank you so much, Minerva", he said through clenched teeth. "That is exactly what I wanted. How very generous of you to share your dinner."
Insofar as it is physically possible for cats to do so, the cat was smirking.