Turkey Vulture survival is reduced in areas of greater road density

The demography of, and factors that influence these metrics, are largely
unknown for most vultures in the Americas. Survivorship of Turkey Vultures
(Cathartes aura) may be influenced by landscape heterogeneity and human
disturbance. We quantified the effects of landscape composition (Shannon’s
diversity index) and configuration (contagion, edge density, and largest
patch index), and human disturbance (road density) on the annual and
seasonal survival probabilities of the 3 North American breeding
populations (western, central, and eastern) of Turkey Vultures that spend
the nonbreeding season in the southeastern portion of the Nearctic and the
northern Neotropics during a 17-yr period. We used Cox’s proportional
hazards models with time-varying covariates to estimate spatial and
temporal changes in survival rates of adult Turkey Vultures. Road density,
but not landscape composition or configuration, influenced survival rates
in space and time. Overall annual survival averaged 0.87 (95% CI:
0.74–0.98). Mortality risk was low in western and central populations
(hazard ratio < 1) but was 3.7 times greater for vultures in
the eastern population. Survival during the breeding (0.97, 95% CI:
0.96–0.98) and outbound migration (1.0, 95% CI: 1–1) seasons was
significantly higher than the other seasons. Average survival tended to be
higher for nonbreeding (0.81, 95% CI: 0.71–0.88) compared to return
migration (0.69, 95% CI: 0.56–0.81) seasons. Risk of mortality for all
vulture populations increased with road density, and this was greater
during the nonbreeding and return migration seasons. The spatial variation
in road density across the Americas may generate a network of ecological
traps for Turkey Vultures induced to stop in areas of greater road-kill
abundance. Road-killed animals acting as an attractant for vultures can
increase the occurrence of vulture-vehicle collisions and potentially
aggravate human-wildlife conflicts. Further analyses are needed to address
survivorship and mortality factors for young birds. Our results may help
the implementation of specific mitigation efforts to reduce human–vulture
conflicts and vulture mortality. For instance, concentrating efforts to
remove road-killed animals in areas where road density is highest can
likely reduce vulture–vehicle collisions and associated mortalities of
these birds.