Latitude sets the season, not the bout length
It is tempting to treat latitude as a master dial for hibernation: colder, higher-latitude places should mean longer torpor bouts. The Arctic ground squirrel work complicates that picture. Two populations living near each other in Northern Alaska differed in the timing of hibernation and breeding, and those differences tracked local environmental conditions rather than latitude alone [2]. In other words, animals at essentially the same latitude can still run their seasonal clocks differently.
That matters for maximum torpor bout length because a bout is embedded in a schedule. If populations at the same latitude shift when hibernation starts, when breeding follows, and how seasonal events are sequenced, the room available for any single long bout can shift too [2]. The study also found sex-specific differences in timing, which suggests that the same environment can produce different hibernation schedules for males and females [2]. Latitude describes the setting; local conditions and the animal's own schedule describe what happens inside it.
A bout is a stretch of deep dormancy inside a longer hibernation
Hibernation is not one continuous sleep. It is a series of long bouts of torpor, the state in which body temperature and metabolism drop sharply [2]. Maximum torpor bout length is therefore the longest single stretch an animal can sustain in that state before it must arouse, and arousals are energetically expensive interruptions.
This framing helps explain why latitude alone cannot settle the question. A bout length is a physiological limit expressed within an ecological timetable. The Arctic ground squirrel evidence shows the timetable itself varies between nearby populations and between the sexes [2], so the same physiological capacity could yield different observed maximum bouts depending on local conditions and scheduling.
Which species-specific costs and benefits are actually supported
The strongest species-specific signal in this evidence concerns bats. A review of climate change impacts on bats discusses biogeography, including small range size and high latitude or high altitude, and notes the duration of torpor in free-living greater horseshoe bats [1]. It also frames its aim as creating a picture of species-specific impacts rather than a definitive list [1]. That is a useful caution: the bat literature points to torpor duration as a species-relevant trait, but it does not establish which costs or benefits explain maximum bout length.
For Arctic ground squirrels, the supported species-specific feature is timing: hibernation and breeding events differ between populations and between males and females [2]. That is a scheduling difference, not proof that one sex or population gains a specific benefit from longer bouts. The honest reading is that the evidence supports local environmental conditions and sex-specific timing as sources of variation, while the case for particular costs and benefits of long bouts remains suggestive rather than demonstrated [1][2].
What would settle the remaining variation
To explain what is left after latitude, researchers would need to connect bout length directly to local conditions and to the timing of seasonal events within a population. The Arctic ground squirrel findings show that such local and sex-specific timing differences are real and measurable [2]; the bat review shows that torpor duration varies in free-living animals and that species-specific impacts are a live concern [1]. Neither source, as summarized here, tests maximum torpor bout length against a suite of candidate costs and benefits.
So the best-supported answer is modest. Latitude is a backdrop, local environmental conditions and sex-specific seasonal scheduling are plausible contributors to remaining variation [2], and species-specific costs and benefits of long torpor bouts are not yet pinned down by this evidence [1]. The question stays open precisely because the most relevant studies describe timing and duration without isolating the trade-offs that would explain the maximum.
Sources used in this answer
The impact and implications of climate change for bats
A review of climate change impacts on bats discusses biogeography, latitude, and torpor duration in free-living greater horseshoe bats, and aims to sketch species-specific impacts rather than a definitive list, without explaining variation in maximum torpor bout length.
Phenological variation in annual timing of hibernation and breeding in nearby populations of Arctic ground squirrels
Two nearby Arctic ground squirrel populations in Northern Alaska differed in the timing of hibernation and breeding in ways linked to local environmental conditions, with sex-specific timing differences, but the study did not address maximum torpor bout length.