Guns and Traps Used to Protect Least Terns at Alameda Point

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.  The most recent field report available for Alameda Point is for 2019, obtained through the Freedom of Information Act.

The report describes a variety of methods used to deter or eliminate threats to the nesting terns.  First, loud noises and bright flashes of light are fired from a gun to frighten away an avian predator, called hazing.  Second, the wildlife biologist drives a vehicle toward an avian predator, another form of hazing.  Third, predators are trapped.  And fourth, as a last resort, the biologist is left with no other choice than shooting the predator with a shotgun or rifle or euthanizing. 

While hazing methods to frighten away avian predators can include driving a vehicle toward the bird, normally the biologist will use one of three types of pyrotechnics fired into the air from agun.  Whistlers are like signal flares that emit a high pitched whistle, bright light, and a trail of smoke when fired from a pistol called a signal revolver.

The signal revolver is also used to fire bangers, which travel about 50 yards.  When launched, a delay fuse is ignited, burning for 5-10 seconds. The fuse ignites a charge that causes the banger to explode, resulting in a bang and a flash of light.  For longer distances, a larger banger called a shell cracker is fired from a 12-gauge shotgun producing a louder bang and brighter flash of light.

Four different types of traps can be used for trapping avian and mammal predators, some with live bait animals, some with food bait.  They are caught either in cages or by snaring their talons (feet) in fishline nooses.  The four different types of traps are a Swedish goshawk trap, pigeon harness, Bal-Chatri trap, and cage trap.

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. 

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 four dead raven effigies from poles at the corners of the nesting site.  But when ravens and crows 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 in the Swedish goshawk trap 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.  Studies indicate that those animals that do survive seldom remain at the release sites,” 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 on how far away a raptor can be taken for release, which can diminish success.  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 the two opossums and one cat that wandered into a cage trap attracted by cat food, it was their last meal.  The two crows that entered a cage also suffered a similar fate.  They were either shot or administered a lethal dose of sodium pentobarbital.

American kestrels and peregrine falcons made frequent visits to Alameda Point and were usually frightened away by hazing methods.

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. 

The annual Tern Watch Program, in which volunteers sit in two separate vehicles near the nesting site and report predator sightings, was suspended in 2020 and 2021 due to COVID-19.  The Wildlife Services program continued unsuspended.

A shorter version of this story was published in the Alameda Sun on Thursday, January 6, 2022.

_______________________________

All about the traps – Design and function

Swedish Goshawk Trap:  The goshawk trap is made of wood and wire mesh with two door flaps on top and a compartment on the bottom where the live bait, either a European collared dove or live house mice are placed.  With the two spring-loaded upward facing door flaps open, a bird such as a hawk or falcon, is lured in.  When it lands on the perch holding the doors open, the perch falls, and the doors close. 

Pigeon Harness:  A pigeon harness is a leather harness with 20 to 30 sliding fishing line nooses attached to the top of the harness.  Wildlife Services uses cowhide that they cut and shape to make a harness that covers the entire back of a dove and wraps around the head and both wings, secured underneath the bird with either a buckle or nut and screw.  A European collared dove is brought to the site and kept in an aviary at the Fish and Wildlife Service office until needed.

The report explains that the pigeon harness is tossed from a vehicle so that it lands right side up and the lure bird flaps its wings. The vehicle is then driven away to a location where the trap can be watched. When the target raptor strikes the harness in an attempt to get the lure animal, the feet of the raptor with its long nails, called talons, get caught in the nooses.  “As the raptor tries to fly away, the sliding nooses tighten over the talons and the weights attached to the harness prevent the raptor from flying away,” writes wildlife biologist Dean Pyzik in his report titled California Least Tern Protection Project.  “Once the raptor is restrained, the nooses are clipped using nail clippers or scissors, and the nooses fall off the talon, freeing the raptor.”

Bal-Chatri Trap:  A Bal-Chatri trap is a wire cage 3” x 10” x 12” with at least 30 fishing line nooses on top.  A weight is fastened to the bottom to prevent a raptor from flying away after being trapped in the nooses while trying to get the live house mice in the trap.  It is also tossed from a vehicle when the need arises.  The house mice are also kept at the Fish and Wildlife Service office.

Cage Trap:  A mammalian cage trap is a wire cage 10” x  12” x 32” with a trap door.  Cat food is used to lure mammalian predators such as cats and opossums into traps.  More than a dozen such traps are placed around the 512-acre Nature Reserve and checked daily.

All about the guns – Models

Ruger Model M77/22 bolt-action .22 Long Rifle rimfire with internal AWC sound suppressor;

Benelli M2 semi-auto 12 gauge;

Remington 870 Special Purpose pump 12 gauge shotgun;

Remington 870 Express Magnum pump 12 gauge shotgun;

Bernardelli break-action side by side 12 gauge shotgun;

J. Stevens model 94B break-action single shot 12 gauge shotgun.

6 mm RÖHM signal revolver

Number of animals lethally controlled:  25

Number of different species hazed:  18

Number of animals (all species combined) that were hazed: Hundreds.

Number of animals relocated:  1