when monarch butterfly's migrate to mexico there numbers are estimated at 2 billion .who counts them?

I see you watched 'Life' last night on BBC 1 ! Sir David Attenborough is a national and international treasure and the BBC natural history unit is the best of its kind in the world.

No one counts them, you will recall them hanging from the branches of those specific trees...it is only necessary to count the number hanging from a single branch and then extrapolate the figures for the entire colony. So knowing the number on one branch, and estimating the average number of branches used per tree and then the number of trees used by the colony gives an approximation of 2 billion individuals.

Stunning photography and cinematography throughout, yet again the BBC shows why it is head and shoulders above all the rest !

Estimates of large numbers are usually based on density counts from which the whole population can be guessed. Nowadays measuring the density is done by photographic and computer analyses and no one sits there trying to count individual butterflies or bacteria.

I watched a coach in this (probable NOVA) a month or 2 in the past. It replaced into exciting. the guy pronounced that the cool climate replaced into killing the Monarchs, maximum of which migrated to this one spot in Mexico. He did finally end up blaming it on people suggesting that community logging resulted in cooler forests. I even have observed this observing animal exhibits for extra desirable than 40 years. The final 5 minutes or so is unavoidably used to slam humankind and this crap has been occurring for a minimum of 40 years. If it weren't for the suited equivocations, i presumed it replaced right into a especially exciting indication of cooling in that distinctive area and it replaced into an exciting informative coach. you may desire to be keen to tolerate the properly-known nonsense and take it with a grain of salt.

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They count sample densities, extrapolate, and compare this to estimates from the food they eat to get estimates.

There is a Mexican man, Juan, who for the last 20 years has been posted at the narrowest point of the border with one of those clicker counters.

no one it's an ESTIMATE