Blog # 407 Mobbing: Why Put Up with It?
Moana was peacefully resting on a snag after taking one of her first flights, courtesy of Cindy Sedlacek.
Salt Point’s Moana was peacefully resting on a snag after taking one of her first flights. Without
any movements or other provocation, a group of red-winged blackbirds came from the nearby
A group of crows mobbing Moana, courtesy of Cindy Sedlacek.
park to mob Moana. The attack seemed incongruent as Moana is a fish eater and poses no threat to the blackbirds. The birds harassed her and attempted to nudge her before giving up their challenge. Moana was clueless as to what was happening and just sat there.
A birder or not, you’ve probably noticed a large bird being harassed or mobbed by several smaller birds and wondered what was going on. When a predator is discovered, a bird will give alarm calls to its family and fly at the predator, diverting and harassing it. Often they will make physical contact. Why doesn’t the larger bird defend itself?
Birds may mob anything that they consider to be a danger. The cuckoo, owls, and day-flying raptors are the birds most commonly mobbed, but cats, foxes, snakes, and even humans are regularly on the receiving end.
The most common birds mobbed, the so-called mob’s target birds are falcons, hawks, ravens, eagles, owls, turkey vultures, and even the occasional Osprey. Carrion-eating vultures and fish-eating Ospreys get mobbed even though they are no threats to other birds.
Crow mobbing an Osprey, courtesy of wildbeat.
Barn Swallows, which nest near human structures, are a good example. If a pair of swallows perceives a threat to their nest, they sound the alarm. Neighboring swallows will join it almost immediately to help chase away the intruder, be it a housecat or hawk that is too close.
Sparrows, chickadees, red-winged blackbirds, crows, and other birds routinely mob raptors including Ospreys. Many species of smaller birds will swoop and chase flying or perched large birds, even striking them. At times, even small raptors such as peregrine falcons, sharp-shinned hawks, and Cooper’s hawks may exhibit this behavior, attacking larger birds and sometimes mammals, when they are perceived to be dangerous. Mobbing happens all year but especially during the breeding season as many mobbers are actively defending themselves, their breeding territories, and nests full of eggs or chicks. These small birds may even defend a non-breeding home range to protect themselves and their food source.
Sometimes only a single smaller bird chases the offending bird out of its territory, but mobbing birds know that there’s strength in numbers and have learned to join forces. Once the larger target bird flees, the chase is over. Red-winged blackbirds are famous for mobbing. They will pursue almost any smaller bird or mammal—even humans. Depending on the circumstance, a mobbing with one or two birds can easily become a flock of mixed birds. Sounding alarm calls, the mobbers may attract other birds of other species to join.
A barn owl getting mobbed, courtesy of westernnews.
Owls are commonly mobbed by smaller birds for protection at any time of year. By chasing away a resting owl, smaller birds are safer at night. Masters of camouflage, owls are hard to find and easy to walk past without realizing they are within viewer range. While any single bird would be prey for the owl, in a flock it is protected. A sudden ruckus of birds alarming or mobbing is usually harassing an owl in its resting spots. Often the large target bird, the focus of the mob’s attention, will tolerate the attack for a short time. If the mob does not give up, their target will fly away, usually without any retaliation.
Even though mobbing birds peck at the target bird, they rarely harm them. Why would small birds engage in this seemingly reckless behavior? Attacking is less dangerous than it appears. The smaller birds are typically swifter and more maneuverable than the target bird, making them difficult to catch. The target birds decide it is not worth the energy to defend themselves,
even if they are overwhelmed by the smaller birds. Thus, if harassed, it is easier for the target bird to just leave.
Crows mobbing an Osprey, courtesy of Parsingphase.com
Why don’t crows get eaten when they mob? Doesn’t their size make them worthwhile for a hawk to attack? Red-tailed hawks and eagles have the talons and strength to grab a crow with its talons. However, crows are far more dexterous and agile than eagles or hawks, and with the exception of goshawks, can easily outmaneuver the raptor. Again, the energy cost of pursuing and catching the crow is usually too high.
When Ospreys or other hawks build nests in areas frequented by crows such as at Salt Point, will the Osprey be mobbed by crows, and what will the Osprey’s response be? Ospreys and other raptors fiercely protect their nests and the airspace around them. The local crows seem to know this and usually keep their distance from Orpheus’ nest as if it was a no-fly zone for crows. However, when Orpheus and Ursula are not near the nest, the crows freely harass them as shown by the mobbing of Moana.
Eyes to the sky!
Candace
Candace E. Cornell
Friends of Salt Point, Lansing, NY
Cayuga Lake Osprey Network
EYES TO THE SKY!
WATCH!
READ!
On Osprey Time: Ospreys of the Finger Lakes
VISIT!
HELP PROTECT OSPREYS
Avoid getting too close to nesting sites during the breeding season. If an animal vocalizes when you're near, you are too close! Back off Immediately.
Carry binoculars to view wildlife from afar.
Restore, clean, and preserve lakeshore and wetland habitats.
Recycle used fishing lines, which can be hazardous to Osprey.
Join the Cayuga Osprey Network and volunteer to help monitor
Osprey nests. Write to: cec222@gmail.com
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