Slow recruitment in a red-fox population following poison baiting: a non-invasive mark–recapture analysis

Abstract

Context Optimal management of invasive species should determine the interval between lethal-control operations that will sustain a desired population suppression at minimum cost. This requires an understanding of the species’ rate of recruitment following control. These data are difficult to acquire for vertebrate carnivores such as the red fox (Vulpes vulpes), which are not readily trapped or observed. Aims To provide a long-term evaluation of the effects of 1080 poison baiting on the abundance and extent of movement of red foxes in a semiarid environment. Methods We used non‐invasive DNA sampling of fox hairs in semi-arid Western Australia where the population was subject to two episodes of aerially delivered sodium fluoroacetate (1080) poison baits within 12 months. Sampling took place at ~45-day intervals and individual foxes were identified by genotyping eight microsatellite DNA markers and a gender-specific marker. Open-population and spatially explicit mark–recapture models were used to estimate the density, apparent survival and movements of foxes before and following baiting. Key results Following a severe reduction in density after baiting, fox density during the ensuing 12 months increased slowly (0.01 foxes km–2 month–1), such that density had only reached 22% of pre-baiting levels ~10 months after the initial baiting. Moreover, recovery was non‐linear as population growth was negligible for 6 months, then exhibited a nine-fold increase 7–9 months after control, coincident with the dispersal of juveniles in autumn. Fox movements between recaptures were on average 470% greater after baiting than before, in line with expectations for low-density populations, suggesting that the probability of encountering baits during this period would be higher than before baiting. Conclusions Baiting with 1080 poison significantly reduced the density of foxes, and the low density was sustained for more than 6 months. Foxes moved significantly further between recaptures after baiting when at low densities. Implications Control programs in this region may be carried out at low frequency to suppress fox density to a fraction of unbaited levels. The intensity of follow-up baiting may also be adjusted downwards, to take account of an increased probability of bait encounter in more mobile foxes.

Lethal 1080 baiting continues to reduce European Red Fox (Vulpes vulpes) abundance after more than 25 years of continuous use in south‐west Western Australia

“…Based on analysis of probability of identity statistics in Western Australian foxes, a genotype consisting of five or more microsatellite loci was considered sufficient to distinguish individuals, including full siblings (Berry et al . , ).…”

“…Genotype error checking and correction based on one and two allele mismatches (Paetkau 2004) was conducted as described in Berry et al (2012). Based on analysis of probability of identity statistics in Western Australian foxes, a genotype consisting of five or more microsatellite loci was considered sufficient to distinguish individuals, including full siblings (Berry et al 2012(Berry et al , 2014.…”

Density- and age-dependent reproduction partially compensates culling efforts of invasive non-native American mink

“…The culling area extended to 10,000 km 2 by 2009 and gradually expanded to cover more than 20,000 km 2 in 2013. A cage trap was placed on the raft only when a mink was detected and left in place for a few days or until a mink was caught (38 % of detections resulted in capture in 2006Beirne 2011). A cage trap was placed on the raft only when a mink was detected and left in place for a few days or until a mink was caught (38 % of detections resulted in capture in 2006Beirne 2011).…”

FoxNet: An individual‐based model framework to support management of an invasive predator, the red fox

“…Poison baiting with 1080 (sodium fluoroacetate) is the primary fox management approach in Australia (Saunders, Gentle, & Dickman, 2010). Baiting at large scales (>500 km 2 ) and high densities (≥5 baits per km 2 ) can greatly reduce fox densities, with populations remaining low for several months (Berry et al, 2014;Thomson et al, 2000).…”