Rodent pressure here follows a fairly predictable annual pattern driven by heat, water and food. Knowing the pattern lets you do preventive work in the cheap window instead of remediation in the expensive one.
March to May — build-up
Breeding activity increases as temperatures moderate. Populations that overwintered start expanding, and juveniles disperse to find their own territory. Dispersing juveniles are the ones that find new entry points, so this is when a gap that was never used before starts getting used.
Do now: nothing urgent, but this is when to book an inspection if you want work completed before monsoon. Availability is good and you are not competing with peak-season demand.
June — pre-monsoon heat
The hottest, driest stretch. Surface conditions become genuinely hostile and rodents seek cool, shaded, humid microclimates. Attics are not cool, but wall voids, crawl spaces, garages and irrigated landscaping are.
Water becomes the dominant driver. Drip emitters, AC condensate lines, pet bowls, leaking hose bibs and pool equipment all concentrate rodent traffic toward the structure.
Do now: this is the best exclusion window of the year. Work done in June is preventive and cheaper than the same work in October.
July to September — monsoon
Storms flood washes, burrows and low ground, displacing rodents toward elevated dry shelter. Expect new attic and garage activity in the days following a significant cell. Vegetation growth after rain expands food and cover.
Do now: respond quickly to new noise. A displacement event caught in week one is a small job. Walk the property after storms looking for fresh debris piles against walls and under equipment.
October to November — peak
This is the busiest period, and it catches people off guard because the weather is pleasant. Two things converge: the post-monsoon vegetation flush has supported a larger population, and cooling nights push that population toward heated structures.
Most "it came out of nowhere" calls happen now. It did not come out of nowhere — it was built through the summer.
Do now: act immediately on any sign. Insulation damage accumulates fastest in this window because activity is highest.
December to February — concentration
Fewer new entries, but the animals already inside are settled and breeding in a protected environment. Attic populations can grow substantially over winter without any new access at all.
Citrus fruits through this period, which sustains roof rats when other food is scarce. Fallen fruit matters more in winter than at any other time.
Do now: if you heard something in autumn and it went quiet, do not assume it left. Quiet often means established rather than gone. Winter is a good time for attic inspection because the space is workable.
The one-line version
Seal in May and June. Watch after storms. Expect the peak in October. Do not assume winter silence means the problem resolved itself.
A note on "waiting to see"
The most expensive version of this problem is the one that ran for a season before anyone called. Contaminated insulation, chewed ductwork and a multi-generation population are all outcomes of waiting, and all three cost more than the exclusion work that would have prevented them.
Not sure what you are dealing with?
A free inspection identifies the species, every entry point and the scope of work — in writing, before anyone quotes you a number.
