The endangered California least terns that nest on the old airfield at Alameda Point are well protected during their April to August nesting season.

Fencing keeps people away from the 10-acre sandy nesting site, but it won’t stop other birds and mammals from getting to the eggs and the helpless chicks. Only a well-armed and outfitted predator management officer can effectively deter other animals.

Every year, the U.S. Fish and Wildlife Service hires a wildlife biologist from Wildlife Services, a division of the U.S. Department of Agriculture. Typically used for protecting crops and livestock, the agency is also hired to protect dozens of endangered species every year.

A 2019 field report describes a variety of methods used to deter or eliminate threats to the nesting terns. Loud noises and bright flashes of light are fired from either a pistol or a shotgun to frighten away avian predators or a vehicle is driven toward them, known as hazing. Predators can be trapped and relocated or, as a last resort, the biologist may either shoot or euthanize the predator.

The report listed various guns brought to Alameda Point in 2019. They included one rifle with a silencer and five 12-gauge shotguns of various types. Four different types of traps can be used for trapping avian and mammal predators, some with live bait animals, others with food bait. They are caught either in cages or by snaring their talons (feet) in fishline nooses.

Flying predators like hawks and falcons are the deadliest of threats, especially when they are attempting to feed their own chicks in the vicinity. During the 2012 nesting season, for example, a single American kestrel, which is a small falcon the size of a mourning dove, was responsible for taking 300 least tern chicks, leaving less than 20 to get out alive.

The avian predators observed at the site in 2019 included American crows, American kestrels, white-tailed kites, common ravens, peregrine falcons, burrowing owls, coopers hawks, a merlin, red-tailed hawks, California gulls, western gulls, osprey, and turkey vultures. On several occasions, peregrine falcons and common ravens foraged in the colony resulting in observed predations.

Wildlife Services attempts to deter crows and ravens by hanging dead raven effigies from poles at the corners of the nesting site. But when they persist in flying near the nesting site, they are often lethally removed by shotgun. Three ravens and 14 crows met such a fate in 2019. One red-tailed hawk was also shot, while another red-tailed hawk was trapped and relocated.

“No captured mammals were relocated,” writes wildlife biologist Dean Pyzik in his report titled California Least Tern Protection Project. “Wildlife Services does not consider relocation of mammals to be a biologically sound practice in many situations. Relocated animals suffer considerable stress from relocation activities and territorial disputes,” explains Pyzik. Epidemiologists oppose relocation of mammals because of disease transmission, and California Fish and Wildlife regulations prohibit relocation.

Relocation of live captured raptors such as hawks and falcons, on the other hand, is encouraged because they are better equipped to deal with the stress of relocation. But there are geographical limitations. Peregrine falcons, for example, cannot be taken across state lines. One year, according to a report, a peregrine falcon was captured at Alameda Point and then driven to the California/Oregon border for release. The banded falcon was back at Alameda Point before the wildlife biologist got back.

For two opossums and one cat that wandered into a cage trap attracted by cat food bait, it was their last meal. Two crows that entered a cage also suffered a similar fate. They were either shot or administered a lethal dose of sodium pentobarbital.

The losses of eggs, chicks, fledglings, and adults due to predation in 2019 was below average, partly due to there being fewer nests. In a rolling five-year period from 2016 to 2020, the number of nests were 403, 447, 375, 345, 435, respectively. Four eggs, one chick, eight fledglings that are barely able to fly, and 12 adults were lost to predation in 2019.

Despite losses in 2019, the Alameda Point least tern colony continued its record as having one of the most successful and sustainable reproduction rates in the state. Success is attributed to both the active predator-management program and the reliable supply of small fish in San Francisco Bay for adults to feed to small chicks. The California least terns remain on the endangered species list because there are not enough sustainable breeding colonies around the state.