The first thing to understand when considering this as an objective is that the rats don’t just ‘come to be’ in life – like any living thing out there, they need 3x environmental variables to be present if they are to etch out a living…
FOOD | SHELTER | WARMTH
You’ve only got to remove 1x of these 3x key variables and most likely the environment will no longer be suitable or capable of supporting the animal in question – it’s that delicate a balance.
Food and warmth are fairly obvious variables to understand – we all need that in life.
Shelter is about shielding from the elements, shielding from predators and hence a safe place to breed – essentially a place to ‘nest & rest’ – and animals are very particular about this as nest sites have strong parallels with their ability to generate offspring plus ensure a good survival rate.
For example a bus stop may provide cover from rain but if temperatures are freezing and the location exposed/nowhere near food shops etc. then you are probably going to struggle to find willing participants for breeding let alone ensure any offspring produced have a good chance of survival.
Likewise its exposed location in an area where other people operate also means there’s a good chance someone may steal your children or try to create their own with your partner the minute your elsewhere so you will probably spend a lot of your time defending what’s yours.
So a good nest site is not just about keeping the rain off your head – ‘shelter’ has to cover seclusion as well.
The best nest sites will be taken up by the strongest fittest animals and in turn will attract mating opportunities with equally strong and fit animals – these individuals will correspondingly then have a strong contribution to the population gene pool as their kids will be many and have the best chance of survival.
This all feeds back into promoting the species as a whole so every member of the population indirectly benefits from this strategy.
So back to rat infestations…. If you were to repeatedly see a rat within your back garden then the first thing you should be considering is why? along the food / shelter / warmth basis.
Rats in the back garden would be most likely as follows:
FOOD – refuse, recycling, bird food, composts, pets fed outside, fishing bait stored in sheds, vegetable gardens, fruit trees.
SHELTER – under decking, under sheds, burrows in soft soil, burrows in composts, in garages and essentially any quiet, undisturbed cavity areas.
WARMTH – around AC units, composts (organic heat), close/inside buildings, hot pipes/ducts, bundles of wiring and anywhere similar where a heat source is regularly provided.
So what about rats inside a building, how does that dynamic work?
Well in the vast majority of cases, any rats in a building fabric are actually getting there via the drainage so it’s the link between waste system and building fabric that explains how all the boxes are ticked.
FOOD – primarily the content of the waste system (think of what you scrape off your plate everynight or what the dishwasher pushes out); however they may also supplement this by directly entering your kitchen and taking what’s about.
SHELTER – your wall cavities, floor void, loft etc. are free from predators and secluded locations ideal for breeding plus also close to the drainage/building link should they need a feed.
WARMTH – all houses centrally heated these days and most via a central heating pipework distribution run through the building fabric itself; modern buildings also have plenty of warm insulation and other heat sources like grease ducts, AC units, fridges, wine coolers etc.
So you can see why buildings are a great place for rats to occupy but totally dependent on that link with the waste system – without that link there’s no food to sustain their existence (they can’t just east dust and rubble).
Waste systems don’t really provide much in the way of shelter and warmth though so they need the buildings to give them this.
That’s why rats are called ‘commensal rodents’ – they have co-evolved alongside us to use the houses we build (or caves as it was in the beginning) to provide them with shelter and warmth plus occasional food opportunities.