Readers’ wildlife photos

After a long hiatus, Bruce Lyon, a biology prof at UC Santa Cruz, has returned with some great photos of his favorite bird, the peregrine falcon (Falco peregrinus). Bruce’s narration and IDs are indented, and you can enlarge the photos by clicking on them.

The Beach Boys song, California Girls, has the lyric “I wish they all could be California girls”. For a pair of peregrine falcons (Falco peregrinus) on the coast of Central California the sentiment was instead “I wish they could all be California gulls”. The female of this falcon pair liked to hunt gulls, but only California gulls (Larus californicus).

The falcons were the next-door neighbors of a pair I had watched for almost a decade and reported on several times on WEIT (here, here and here for a few example posts). This newer pair often hunted from home. Perching on the cliffs near their cavity nest site, they spent long periods staring out to sea. Other local peregrines do this in spring to go after migrating shorebirds like phalaropes, but the female of this pair was going for gulls, and she was doing it before nesting. Peregrines can be skittish with prey but this pair was unusually tame with food, which afforded some amazing natural history encounters.

Below: The pair stares out to sea watching for birds. Female peregrines (right) are typically much larger than males  (50-60% larger, depending on region) and this affects the size of prey they can capture.

Below:  On some days hundreds of gulls would fly north, close to the cliffs, taking advantage of updrafts of air deflecting up off the cliffs. Most of the passing gulls were western gulls (Larus occidentalis), a fairly large gull at about 1000 grams (2.2 lbs). Compared to other local gulls, western gulls are darker gray on the back and tops of the wings, and have a stout yellow beak with a red spot near the tip.

Below: Whenever western gulls flew by the cliffs the female ignored them.

California gulls also came through, but in lower numbers. They are considerably smaller (600 grams, 1.3 lbs) than western gulls, with a thinner beak tipped with both a red and black spot, and paler gray on the top of wing and upper back. The yellow legs on breeding adults differ from the pink legs on a western, a handy way to ID a dead gull when the falcons have removed other diagnostic features.

Below: Unlike with western gulls, the female showed intense interest in California gulls. She watched them closely as they flew by, often adopting an ‘ready to pounce’ posture that preceded her launching into action. Interestingly, she did not immediately take off after a gull that was flying but waited to spring into action until after it had disappeared out of sight around a corner in the cliff. My guess is that part of her strategy for catching gulls was a surprise attack at close quarters, and she waited so that a target gull would be unaware of her interest.

Below: Springing into action after a target California gull flew by. Once leaving the cliff she flew rapidly at full bore to catch up to the gull.

The first few times the female went out chasing a gull I was sure of the outcome only when she quickly returned without prey. When she did not return immediately, I initially assumed she had not been successful, for the various peregrines I have watched almost always bring prey back to the nest area. Instead, I figured she had missed the gull but stayed out hunting for other prey since she had already left her perch.

Below: Then one day when she went out in particularly hot pursuit of a gull and did not return, I got suspicious and went looking for her. I found her about 300 yards north of the nest eating the gull, on a ledge above the surf around a corner in the cliff. The black spot on the beak and yellow feet confirmed it was a California gull. Eating a gull where she killed it, rather than returning to the nest area with it, turned out to be the norm for her. The gulls are a very heavy prey item and I suspect it takes too much effort to fly far with something this large.

Below: Eventually the male joined the female at the carcass but at first kept his distance and picked at the entrails off to the side. Female peregrines can be possessive about food, particularly when there are chicks to be fed, but this was in February before nesting. Males are often very deferential, perhaps because the females are so much bigger.

Below: Eventually he joined her at the carcass. I had not previously seen food sharing like this with the other peregrines.

Below. Another California gull kill. Again, when the female went out on a chase and did not return, I went on a search. I found the pair sharing a California gull on a very narrow ledge above a channel, very close to the earlier kill shown above.

Below: I was surprised to see the male feed the female bits of food, as this photo shows. The female is completely capable of feeding herself so perhaps this mate-feeding was a form of bonding?

Below. The male framed by the gull’s wings. It was very gusty and the gull wings kept flapping in the wind and smacking the male falcon in the head. A gust eventually blew the gull off the tiny ledge and it landed on a rocky shelf below, close to a channel of water.

Below. The female went to the fallen carcass and started feeding, but large waves threatened to flood the shelf and the carcass was in danger of being washed out to sea.

Below. The female tried to pull the gull up away from the danger zone but she was not successful. Eventually a very large wave flowed over the rock shelf and the receding water dragged the gull out to sea. I watched for a few minutes and the falcons did not retrieve the gull from the water.

Below. Later when this pair had chicks. they did bring gulls to the nest, as shown here where the female sits close to the nest with a gull. The parents often eat part of a prey item before bringing it back to the nest, so perhaps the gulls brought to the nest were partially consumed and easier to carry in flight.

I never saw this female actually catch a gull because the captures always took place around the corner out of sight. However, some friends did see a capture—the female pursued a gull, caught up to it, pounced on its back and wrangled it down to the ground. They did see how the gull was dispatched.

Below: I did see the the female of the neighboring pair take out a California gull. In my peripheral vision I saw what I assumed were two gulls fighting in the air well off in the distance and they slowly spiraled to the ground locked together. Something did not seem quite right for a gull fight so I hiked over to the spot and to my surprise I flushed the female falcon off the ground with a freshly killed California gull. The ‘gull fight’ had actually been a peregrine kill.

Perhaps because I spooked her and she was already in the air flying with the heavy load, the falcon did fly with the gull the 500 meters back towards her nest. Her flight seemed really labored.

Below: A second western gull was not amused by the situation and chased the female falcon back to the nest.

Below. ‘On a wing and a prayer’. When eating small birds, the falcons typically pluck all the flight feathers from the wing but they do not do this with large prey like gulls. This leaves a pair of intact wings attached to the carcass, and the falcons sometimes fly around with these winged carcasses, as shown here. The expression—on a wing and a prayer—refers to taking on an endeavor with little chance of success. This may seem apt for the falcons when hunting gulls because the probability of a successful kill for a given chase seems considerably lower than for some prey like phalaropes. In terms of bang for buck, however, gulls are likely worth the effort  because a gull is about 20 times heavier than a phalarope.