We note elsewhere that
the estrus (heat) of the female cat is unpredictable, and that there is no “regularity” involved in cats. Let’s qualify that observation with this bit of information: as a general rule, the female cat is more likely to be in heat when the days are lengthening—that is, after late December, when the amount of daylight increases with every passing day. (This is true in the northern hemisphere.
In the southern hemisphere, days begin to lengthen in late
June.) Veterinarians speak of cats as “long day” breeders, since the females (and the females of several other species) are more likely to be in heat from (roughly) January through September.
