Anthropogenic mortality threatens the survival of Canarian houbara bustards

Abstract

Anthropogenic mortality is a major cause of global mortality in terrestrial vertebrates. Quantifying its impact on the dynamics of threatened species is essential to improve their conservation. We investigated cause-specific mortality in Canarian houbara bustards (Chlamydotis undulata fuertaventurae), an endangered subspecies endemic to the Canary Islands. We monitored 51 individuals tagged with solar-powered GSM/GPRS loggers for an average of 3.15 years, and recorded 7 casualties at aerial lines (13.73% of the sample; 5 at power lines, 2 at telephone lines), 1 (1.96%) at a wire fence, 4 road kills (7.84%) and 1 case of predation by cat (1.96%). Cox proportional hazards models showed that anthropogenic and natural annual mortality rates were similar (respectively, 6.20% and 6.36% of the individuals). We estimate that 33-35 houbaras die each year in the Canary Islands due to anthropogenic causes. Population viability models using these data and juvenile productivity values obtained over seven years predicted the extinction of the species in 50 years. Eliminating anthropogenic mortality, the population could be recovered, but would still require management actions to improve habitat quality. Conservation measures to reduce anthropogenic mortality due to power line fatalities, roadkills and predation by cats, as well as to increase productivity, are urgently needed, particularly on Fuerteventura, where houbaras are on the brink of extinction.

Figure 1

Cumulative incidence function for houbara bustard mortality cause (anthropogenic vs natural) in the Canary Islands. Time is given in days.

Figure 2

Survival probability functions of houbara bustards in the Canary Islands obtained using ‘survfit’ of the ‘survival’ package and assuming two scenarios: all causes of mortality operating (i.e., natural and anthropogenic, red dots) and only natural mortality (i.e., anthropogenic sources suppressed, black dots). Survival estimates and standard errors are given. See Supplementary Table S2 for details.

Figure 3

Simulated trajectories of the houbara bustard population of the Canary Islands (n = 577 individuals) over 50 years under two scenarios, natural mortality only or both natural and anthropogenic mortality. For each simulation, the exponential rate of increase (mean and SD), probability of extinction, final population size and mean genetic diversity (or expected heterozygosity) remaining in the extant population are given. The values for an extended simulation period of 100 years are also given. The mean time to first extinction under natural mortality only was 44.32 years (SD = 4.27). Supplementary Fig. S1 online shows simulations run independently for each of the two main islands (Lanzarote, Fuerteventura).