Young wild horses being loaded into a trailer during the Antelope Valley roundup. © The Cloud Foundation
The foundation called the limitations to visiting horses gathered from the Calico complex as severe and said it has been left wondering what the bureau was hiding.
The bureau said the cutback from three public visitation days a week to one, on Sundays, was due to work getting the horses prepared for adoption - freezemarking, vaccinations, blood tests, deworming, and recording descriptions of each animal.
It said horses would be in the facility's alleyways continuously and it was not possible to safely host visitors during preparation work.
The bureau said visitors had to be co-ordinated with the operator of the facility at Fallon to ensure there was no interference with day-to-day operations.
The Clound Foundation said that despite the enormous cost of the muster, the bureau was denying requests for independent humane observers during the processing of the horses.
"I've been watching the processing of mustangs on and off for 15 years. What is the big deal this time?" asked Ginger Kathrens, volunteer executive director of the foundation.
"There's something very wrong when it's easier to crash a party at the White House than go view our wild horses being freeze-branded in Nevada."
Wild horse advocates have been angered by the deaths of 49 horses as a result of the roundup, as well as abortions in more than 30 mares.
The 4 per cent death rate is over eight times the bureau's expected level for a helicopter roundup, it said. Foals are now being born in the pens and the public is not permitted to confirm young, sick and old animals are being humanely treated in a timely fashion.
The foundation said that given the high level of interest, the bureau should figure out a way to safely allow the public to observe.
Wildlife ecologist and Nevada wild horse advocate Craig Downer said: "Processing our wild horses in secret does nothing but promote suspicion on the part of the public who simply request to have independent representatives present to verify that our horses are being treated humanely.
"Denying American citizens the right to watch over their horses is a very disturbing trend, and simply throws fuel on a spreading fire."
The muster gathered 1922 wild horses over a 40-day period.
It said the bureau had adopted a "bunker" mentality which had trumped any requests for transparency.
Wild horse advocates want a moratorium on gathers pending discussion and development of long-term strategies for their management.