Effects of aerial 1080 operations on deer populations in New Zealand

Abstract

Aerially distributed baits containing sodium fluoroacetate (1080) are used in New Zealand for smallmammal pest control over an average of about 600 000 ha each year. This can also kill non-target species, including deer. This incidental mortality of deer generates antipathy to 1080 amongst many hunters, adding to the broader opposition to aerial 1080. Hunter opposition to 1080 baiting has also prompted the development of deer-repellent 1080 bait formulations. Historical estimates of deer mortality varied widely but were sometimes high. However, a recent study showed no adverse impact of 1080 on red deer sighting rates in one area and suggested that modern baiting protocols and frequency may have reduced the risk to deer. Here we provide a broader review of deer mortality observed in 26 aerial 1080 operations (or part operations) conducted since 1999. The estimated mortality of deer ranged from 0% to 100%. Overall, 42%, 38% and 20% of operations were classed as having low (0 to 33%), moderate (34 to 66%) or high (67 to 100%) impacts on deer populations, respectively. Adult males were found dead less often than adult females and all other age/sex classes, suggesting that by-kill risk might sometimes be inversely related to body size. Lower sowing rates (0.25-1.5 kg ha −1) more often resulted in low deer by-kill than higher sowing rates (2.0-3.1 kg ha −1), but there was no indication that using larger (12 g) rather than smaller (6 g) baits increased deer mortality. There was some indication that mortality may be lower where 1080 operation had been repeated within 5 years, possibly because of learned bait aversion in survivors of previous operations. The determinants of incidental mortality of deer are complex and somewhat unpredictable, and some deer are likely to be killed in most if not all operations, irrespective of the baiting strategy. We recommend formally planned experiments (rather than gathering often informal observations as summarised here) to assess whether deer mortality is significantly reduced when low sowing rates and/or short-interval repeat baiting is used, and (if so) whether this jeopardises efficacy in possum and rat control.

Dual aerial 1080 baiting operation removes predators at a large spatial scale

“…Blackbirds are be affected by aerial 1080 operations (Morriss et al 2016;Van Vianen et al 2018), as are red deer with variable results (Malham et al 2019;Nugent & Fraser 2005;Graham Nugent et al 2019). We could not use deer repellent in conjunction with kea risk mitigation strategies, and although historical impacts of 1080 operations on deer have been highly variable, impacts can increase with higher rates of sowing (Morriss et al 2020).…”

Effectiveness and costs of helicopter-based shooting of deer

“…The proportion of the population killed, or population reduction, is commonly used to quantify the effectiveness of vertebrate pest control operations (Veltman and Pinder 2001;Morriss et al 2020). A higher population reduction per unit effort or cost is desirable (Veltman and Pinder 2001), but other factors such as social acceptability (Forsyth et al 2017) and animal welfare outcomes (Hampton et al 2022) need to be considered.…”

“…The proportion of the population killed, or population reduction, is commonly used to quantify the effectiveness of vertebrate pest control operations (Veltman and Pinder 2001; Morriss et al . 2020).…”

Relative efficiency of hunting methods during an incomplete Sitka black‐tailed deer eradication on Haida Gwaii, Canada

“…The literature suggests that the most cost‐effective way to severely cull deer populations at high density is the use of the toxicant sodium fluoroacetate (1080), which is a natural chemical derived from Gastrolobium that biodegrades rapidly after deployment (https://www.doc.govt.nz/nature/pests-and-threats/methods-of-control/1080/why-we-use-1080/). Aerial 1080 deployment has an estimated cost of $33/ha or $3300 per km 2 (1.67 heli hours cost per km 2 equivalence) for small invasive mammal reductions (Morriss et al., 2020) where incidental deer kill rates ranged from 5% to 93% with a mean mortality rate of 50% (Nugent et al., 2001) with rates determined by bait preference, sowing density (kg/ha), ungulate size (smaller bodied species had higher mortality) and the toxicant naivete of the population (Morriss et al., 2020). This method was originally considered for Gwaii Haanas but was not adopted as it is not registered in Canada for vertebrates, by‐kill was likely and the meat would not have been safe for human consumption, which was critical in the local context.…”

“…nz/ nature/ pests -and-threa ts/ metho ds-of-contr ol/ 1080/ why-we-use-1080/ ). Aerial 1080 deployment has an estimated cost of $33/ha or $3300 per km 2 (1.67 heli hours cost per km 2 equivalence) for small invasive mammal reductions (Morriss et al, 2020) where incidental deer kill rates ranged from 5% to 93% with a mean mortality rate of 50% (Nugent et al, 2001) with rates determined by bait preference, sowing density (kg/ ha), ungulate size (smaller bodied species had higher mortality)…”