A tale of two kites

Two large, graceful raptor species glide over the plains of the Extremadura region of Spain, but the population of one species, the Red Kite, is in serious decline, while the other, the Black Kite, is expanding its range and quickly becoming the most numerous raptor in Europe. Inquiring minds want to know why…so I consulted our fabulous bird guides (Alan Davies and Ruth Miller of birdwatchingtrips.co.uk) for an explanation.

Red Kites are elegant flyers, with long (almost 6-foot) wings for their up to 3-pound body size. Truly a gorgeous bird with their cinnamon-colored bodies, brilliant white under-wing patches, and black wing tips.

Black Kites are smaller in body mass (up to 2.5 lb) and body length with a shorter wingspan (~5 feet) than Red Kites and have a wedge-shaped tail (instead of forked one like the Red Kites). They also vary greatly in color, ranging from very dark brown-black to lighter brown with reddish highlights, which confuses the casual observer like me. But the top (dorsal) side of their wings is definitely darker than that of the Red Kites.

Feathers that cover the wings of the Red Kite (over the flight feathers) have darker centers and lighter margins, giving them a sort of striped look. In contrast to similar-sized Buteo hawks (like our Red-tailed and Red-shouldered) of North America, adult Kites have pale eyes and juvenile birds have dark eyes.

Body and flight feather coverts of Black Kites are more homogeneous in color than those of Red Kites.

But there is more than just morphology that differentiates these two species — behaviorally, they are quite different as well, and this is part of the reason for the difference in their abundance in the Extremadura region.

Both Kite species depend heavily on scavenging on carrion of sheep or cattle carcasses and roadkill, but also hunt live prey, gliding down and snatching them off the ground and effortlessly moving back upward to soar to a perch to eat what they have grabbed. Red Kites particularly like a diet of earthworms in the spring — strange food for such a large bird. As scavengers, Red Kites seem particularly susceptible to poisoning, from illegal baits set for other predators like foxes, which somehow Black Kites either avoid or are less affected by.

Black Kites are widespread and common. They range from Europe to Asia in the temperate zone, and can also be found in sub-Saharan regions of Africa, parts of the Middle East, India and southeast Asia. In the winter they form large gregarious roost, and often flock to carrion in large groups, much like vultures.

Red Kites have a much narrower range than Black Kites — in fact, Spain is the southern end of their distribution which spans primarily the northern parts of western Europe, including the UK and parts of Sweden. Red Kites also roost communally during the winter, then migrate south to Extremadura and Donaña National Park to breed. However, breeding success in Donaña has declined drastically in the last 20 years, with a 90% reduction in the number of chicks produced there.

Lastly, Black Kites are a highly opportunistic species, changing their foraging strategy to suit the “prey” (including carrion) availability, and they seem to be less affected by human disturbance, even nesting in close proximity to roads and houses.

The nest of this Black Kite was right outside the roadside restaurant where we had just eaten lunch.

A number of reasons have been suggested for the difference in the success of these two, very similar species: susceptibility of the Red Kite to poisoning, disruption of breeding habitat for the Red Kite, availability of natural prey for the Red Kite, like mice and rabbits who are also limited by conversion of habitat to agriculture, and lastly, climate change that has resulted in drought and vegetation changes that make the landscape unsuitable for Red Kite survival. Among the laws of nature, it’s “adapt or die” to change. And the Black Kite seems to be the more adaptable.