Deer survive 1080 drop
Scientists encountered more deer in South Westland forest blocks after 1080 drops than before the drops. In a further unexpected result, they also encountered and saw the same numbers of deer in 1080 drop zones as they did in zones where 1080 was not dropped.
Trends in deer encounters and sightings were also similar inside and outside drop zones. ‘‘Deer were more conspicuous immediately after 1080 than they were later on,’’ said Dr Susan Walker of Landcare Research in an interview.
‘‘That was completely unexpected and very interesting. We really don’t know what the mechanism was but it was a very strong effect in the data. That’s absolutely fascinating,’’ she said.
The Department of Conservation and many others accept that the 1080 toxin used to suppress pests such as possums also kill deer.
A debate has raged over how many deer are killed by the poison. Some argue 1080 is widely fatal.
‘‘But these data from South Westland show that whether or not some deer were killed by 1080, the numbers of deer seen and encountered in 1080-treated blocks did not decrease compared to untreated blocks,’’ she wrote in an email.
The deer data were gathered in the course of other studies by DOC and others looking at rat populations and bird song in seven forest blocks in Westland.
For the purposes of these other studies, four of the blocks were treated to aerial drops of 1080 and three were not.
Technicians visited all of the blocks four times a year between November 2011 and August 2015, mostly to monitor rat tracking tunnels and to service bird song recorders.
And while in the bush, they recorded deer ‘‘encounters’’ – animals either seen or heard. In total, there were 442 encounters with deer, and 288 individual deer were seen by human eyes.
‘‘Across the whole study period, numbers of deer encountered and seen were similar in blocks treated with 1080 to those in the untreated blocks,’’ reported Walker and colleagues in a new paper in the peer-reviewed NZ Journal of Ecology.
Moreover, ‘‘within the [1080] treated blocks alone, our models showed that there were significantly more encounters and deer seen soon after a 1080 operation than later’’, they found.
This effect was most pronounced in the first 12 months after the drop and tapered off over time.
‘‘We found no evidence of even short-term negative effects of aerial 1080 operations on numbers of deer encountered and seen. This result is the opposite of that which would be expected if aerial 1080 operations reduced numbers,’’ they wrote.
The researchers accounted for the calendar month to rule out more deer being encountered in spring, for example, and other possible confounding effects.
The field workers recorded two dead deer. Walker acknowledged the workers were not looking for deer corpses but moving between research locations as efficiently as possible, given the mountainous terrain and mostly thick forest.
However, they were not moving quietly or sneaking up on animals.
Walker and colleagues attempted to explain why more deer were encountered after 1080 drops. Their favoured hypothesis was that 1080 operations have lethal or sublethal effects that ‘‘disrupt the social organisation of the population’’, [and] animals [were] in a process of social reorganisation’’.
If that was happening, deer ‘‘might exhibit less wary behaviours resulting in the higher numbers of encounters and sightings’’. But they don’t really know.
The Dunedin-based researcher said the findings matched her personal experiences on the West Coast, where she often travels.
‘‘I’m familiar with the landscape . . . it’s kind of a homepatch. It’s the first study I’ve seen that actually counts live deer, in a way that a hunter would experience them,’’ she said.
The numbers of deer seen in 1080-treated blocks did not decrease.