How many birds are killed by cars on New Zealand roads, and does it matter?

Abstract

For ten years now, I’ve been logging the road kill on my bike ride to Lincoln University from Christchurch city. I’ve also been counting the live birds and mammals I see and hear. It has been eye-opening to discover how many birds are killed each year. Mammal carcasses are much more apparent and substantially longer-lived than bird carcasses which has led to the mistaken impression that cars kill many more mammals than birds. Along the 17 km length of my main route, on average I nd one bird killed per kilometre every 10 days,

while I nd one mammal every 28 days. I use my estimates of carcass persistence to re ne estimates of the total bird mortality along these roads. If my surveyed roads are representative of urban and peri-urban roads nationally, then the national bird road toll is easily equivalent to several Rena oil spills each year. But what difference does that make to bird populations around our cities? I combine my road kill counts with estimates of local bird populations derived from my live count data, to estimate the proportion of bird populations lost to cars. I then ask whether rarer birds in the landscape tend to be most impacted. Based on my preliminary calculations, in areas with fast-moving traf c around the fringes of cities, more post- edging birds appear to be killed by cars than by mammalian predators, including cats.