Cross over point

[Into the lions den]

And on the original topic?

'Crossover day' is a term I came up with quite some years ago and its is simply the day on which the rate of new bees hatching first exceeds the rate the old bees are dying off.

It is colony specific, not calendar specific or even apiary specific.

Colonies, even within one apiary can experience crossover day on quite widely divergent dates. Depends on many factors (its a long list...not posting it here right now). Low strength colonies tend to struggle to keep enough brood warm early on and their crossover day can be delayed until (3 weeks after) ambient temps allow a high brood to nest bees ratio. Small colonies may never get there without a bees boost, and the decline (spring dwindle as PolyHive et al would know it of old) continues past the point of no return or to the point the colony just struggles on and only gets there as the June gap sets in and then it never prospers.

Its quite big topic even if deceptively simple.

 

[Into the lions den]

To get back to the original question. If the colony is still alive on 1st March, in the UK they have survived winter as meterologically it’s spring.

In our experience, directly winter related losses are only at about 10% of their final level at the end of January, and about 50% by the end of March. More colonies die in April than any other month...at least up here.

Lots of beekeepers have little self deluding tricks to deny or minimise their winter losses....seemingly mostly to try to impress other beekeepers or to sanctify their pet bees as something special (not many actually are).

This always makes our admitted losses seem high compared to others. All the following result in -1 from the total, and are thus a loss we take into our calculated rate. Anything less is kidding yourself.

1. Any colony eliminated at summers end for whatever reason, be it shaking out as queenless or a drone layer, or considered small and united to another. Its still -1
2. Starvation cases...at whatever time between harvest and spring.
3. Winter dead outs. ALL causes. Nosema, queenless, mice, weather, dysentery, bad feed, beekeeper neglect.
4. Spring duds. Its mostly back to queenless and drone layers again but there can be other causes such as poorly mated queens that do not lay properly, spotty brood colonies that don't prosper (inbreeding?), and anything that means the colony is culled or united to another.
5. Disease culls in season. Can be AFB, EFB, severe chalk brood, viruses.

Reasonable to exclude class 5 from 'winter' losses but the rest have to be included. What you peaked at in the summer compared to what you have after crossover and culls is what your winter loss rate is.