To understand when to hunt, and what the bulls will look like when you find them, it helps to walk through the tahr year.
In late spring and through summer (November through March in the Southern Hemisphere), bulls live separately from the nanny groups in loose bachelor mobs of three or four. They are reddish-brown, the cape is short, the mane is thin behind the shoulders. They feed high, often on the upper alpine grasses and herbs. A trophy bull shot in summer makes a thin, ragged cape. Outfitters do not run trophy hunts in summer for that reason.
Through late March and into April the winter coat starts to come in. The mane lengthens. The body colour begins to darken. By mid- to late April the cape has thickened; by early May it is nearly there. The bulls are starting to drift down out of the bachelor groups and seek out the nannies.
From around the second half of April through to early July, depending on the season and the latitude, the rut rolls through the country. This is the period that defines tahr hunting. Mature bulls go into the nanny basins, fight, post on prominent ridges, and chase. They roar and grunt — a hoarse, low call that carries across alpine basins. A herd bull might gather and hold a group of fifteen, twenty, thirty or even fifty nannies and kids. He will lose substantial body fat over a few weeks and then drift back to the bachelor groups in spring.
By May and June the bulls are at their peak: full mane, dark almost-black face, dark hindquarters, sometimes faint pale "kidney stripes" running either side of the spine. The skirt of long hair underneath the belly hangs low. From mid-March through to the end of August the cape is good for taxidermy; the mid-May through mid-July window is the picture-postcard, lion-of-the-mountain peak.
Through August the bulls start moving back uphill and the cape begins to thin. By spring the mane sheds and the bulls slowly drift toward their summer state again.
Two practical implications follow.
If you want a trophy mount, book between the start of May and the second week of July. Earlier and you get a thinner cape; later and the daylight is short and the weather brutal, and the cape begins to deteriorate.
If you want pure population control work — culling nannies and juveniles — you can do that through the off-season. Some outfitters run dedicated nanny-cull weeks for hunters who want time on the hill without paying trophy prices.
A note on rut behaviour. Bulls in the rut are intensely focused on nannies. They will sometimes ignore a stalk that would otherwise spook them. They will sometimes take a wrong cross-canyon wind because they are watching another bull. None of this means they are easy. But the rut is the only time of year a bull will leave his bluffs in daylight to chase across an open face, and that visibility is what makes it the trophy window.