What’s killing San Francisco’s parrots of Telegraph Hill?
A common rat poison has sickened or killed many free-flying parrots from the famous flock that resides in the Telegraph Hill area in north San Francisco
NOTE: Originally published under the title “Rat Poison Is Killing San Francisco’s Parrots Of Telegraph Hill”
A common rat poison, bromethalin, has been found to be sickening or killing feral parakeets (also known as conures [KON yerz]) from the famous flock that resides in the Telegraph Hill area in north San Francisco, according to a team of scientists and veterinarians. The newly published study is the result of a decade-long effort to determine the cause of a mysterious and often-fatal collection of neurological symptoms that have plagued the parrots from this particular flock since at least 1999 (ref).
These personable parrots were made internationally famous by the book, The Parrots of Telegraph Hill, by Mark Bittner (who was homeless at the time) and a 2003 independent full-length documentary with the same name.
It’s estimated there are 300 or more of these medium-sized emerald green parrots with flaming carmine faces and pointy tails currently flying freely above the densely populated urban areas of San Francisco, and where they commonly interact with local residents and tourists.
The parrots form a naturalized flock that typically roost in the Telegraph Hill area in northern San Francisco. The flock consists of three closely-related species, each originating from its own distinct and non-overlapping range in South America: mitred, Aratinga mitrata, red-masked (also known as red-headed or cherry-head), A. erythrogenys, and red-fronted (also known as scarlet-fronted), A. wagleri, parakeets and their offspring, which are often hybrids.
Although these parrots are introduced species, they reside only in urban areas, where they nest and feed on exotic ornamental plants and at backyard bird feeders.
San Francisco’s feral parrots’ mysterious symptoms had no obvious cause
Eventually, the parrots’ neurological symptoms became so worrying that San Francisco passed a law making it illegal to feed the parrots because it was suspected that their health was being damaged by being fed too much junk food by their admirers. Despite this, the number of these mysterious cases grew between 2003 and 2018. As a result, more and more incapacitated parrots began showing up at local animal rescues, shelters, and veterinarians’ offices.
“Because conures are psittacines, they were usually referred to Mickaboo Companion Bird Rescue,” said lead author of the study, avian veterinarian Fern Van Sant, whose clinic, For the Birds, provided medical care for many of the stricken parrots.
Mickaboo is a large volunteer organization in the greater San Francisco Bay Area that responds quickly and effectively to companion parrots in need by providing them with medical care and housing.
Because parrots are non-native and feral, it was initially assumed by both animal control and by local wildlife rescue groups that these ailing parrots were lost pets. Wild bird rescues, which typically have only enough funding to deal with wild bird species, were unable to help. So the city’s animal shelter asked Mickaboo to take in what was assumed to be an occasional injured or sick bird. But Mickaboo quickly became established as the local guardians for all parrots, both captive and feral.
“They became a ‘go to’ for injured and sick feral conures,” Dr. Van Sant said.
Mickaboo provided care for these feral parrots that was just as proactive and thorough as care provided to companion parrots.
“Mickaboo’s role in this investigation has always been the same as it is in caring for all of the birds we rescue — to try to find the best possible care for our birds,” said Michelle Yesney, CEO of Mickaboo. “This always includes trying to find a treatment, preferably a cure, for whatever is wrong. We take in the birds and provide whatever veterinary care is necessary. Sometimes it involves specialists.”
But these feral parrots were suffering from an unusual collection of neurological symptoms — and even when they survived, they never seemed to fully recover.
“For a bird rescue, caring for ANY bird with these kinds of symptoms is traumatic. Taking them in repeatedly is heartbreaking,” Ms. Yesney said in email. “We work with several excellent avian vets, and none of them could find an underlying cause for this condition. Various possibilities were investigated, and none of them proved to be the cause.”
Confused and deeply concerned, the volunteers at Mickaboo were grimly determined to finally identify the cause of these parrots’ perplexing symptoms so they might prevent their terrible deaths. Little did they know at the time, but tracking down the cause of these parrots’ illness would lead them on a decade-long scientific and veterinary quest for answers.
Mickaboo launches an investigation
“The investigation, inspired and funded by Mickaboo, required a team of veterinarians, pathologists and researchers,” Dr. Van Sant said in email.
According to Ms. Yesney, Mickaboo paid for most of the required lab work and hospital care, whilst most of the parrots’ veterinary care was provided either at a discount or free of charge.
“The feral conures have a huge fan base in SF,” Dr. Van Sant pointed out in email. Thus, when injured or ill parrots are discovered by members of the public, they typically are taken to local veterinarians rather than being ignored.
Because of their central role in overseeing these parrots’ healthcare, Mickaboo collected and maintained medical information on 158 San Francisco parrots that were suffering from this mysterious neurological affliction between 2003 and 2018. According to these records, 55 parrots died, 53 were adopted, 25 are still in foster care, and 22 were released (and three escaped) back into the “wilds” of urban San Francisco.
A team of researchers comes together to identify the cause
In their recently-published study, Dr. Van Sant and her collaborators focused their efforts on four parrots that received veterinary care in 2018 because they were showing the same, peculiar collection of neurological symptoms (ref). These symptoms included uncoordinated movements (ataxia), seizures and disorientation. Three of these study parrots, like so many before them, were euthanized when their condition worsened to the point where they could no longer feed themselves.
“It became apparent over time that there was an unusual set of neurologic symptoms that were very unique but consistent,” Dr. Van Sant said in email. “We began the investigation on all deceased conures that exhibited these symptoms.”
Because some viruses, such as West Nile Virus, or heavy metals, such as lead, can produce neurological symptoms in their victims, 15 similar cases from 2013 through 2017 were screened for these agents.
“As these were ruled out, the consistent finding of vacuolar degeneration in the brain was deemed significant and not artifactual,” Dr. Van Sant said in email. “Because the very unusual symptoms were consistent with bromethalin, we continued our inquiry as neurologic conure patients were found.”
However, several established labs couldn’t find any traces of bromethalin.
“One of our vets, Dr. Van Sant, had a professional relationship with Dr. [Branson] Richie at the University of Georgia, who is an internationally recognized virologist. He became interested in the problem,” Ms. Yesney said in email. “Over time, Dr. Van Sant and Dr. Richie brought together the research team that completed the study.”
Fecal samples, collected from the four study parrots when they were first hospitalized, were sent to the Infectious Diseases Laboratory and Center for Applied Isotope Studies at the University of Georgia for testing. When pathologists examined the three study parrots that had later died, they discovered lesions in the birds’ central nervous systems, which suggested bromethalin poisoning as the possible culprit.
There is no test to detect bromethalin poisoning
Bromethalin is a neurotoxin that has increasingly been replacing blood thinners in many commonly used rat poisons since 2011 because rats and other rodent pests have evolved resistance to them. The switch to bromethalin was also prompted by a 2008 EPA directive intended to make rodenticides safer in the event of accidental ingestion by children, pets or wildlife (ref).
Unfortunately, this poison is having the opposite effect. For example, the Pet Poison Helpline reported a 65% increase in bromethalin toxicosis cases between 2011 and 2014 (ref). Amongst common household pets, cats are known to be most susceptible to bromethalin poisoning, whilst rabbits are least susceptible — and guinea pigs are not affected at all. These differences in bromethalin susceptibility likely stem from metabolic differences between species.
Currently, there is no test available to identify bromethalin poisoning. But Dr. Richie’s colleagues specifically adapted high-performance liquid chromatography (HPLC) to detect bromethalin. HPLC is a widely-used analytical chemistry technique that separates, identifies, and quantifies each component in a mixture. When fecal samples from the study parrots were subjected to HPLC, they all tested positive for bromethalin, and half were discovered to also contain desmethyl-bromethalin.
Desmethyl-bromethalin is bromethalin’s toxic metabolite that does most of the damage and the killing. After ingestion, bromethalin is rapidly absorbed from the intestines and is metabolized by the liver to desmethyl-bromethalin. Both bromethalin and its metabolite accumulate in the brain and the liver, where they cause permanent damage.
Using HPLC, Dr. Richie’s lab detected bromethalin in both brain and liver samples from the three study parrots that died and also identified desmethyl-bromethalin in all but one brain sample.
“It has literally taken years to refine diagnostic and testing protocols that unequivocally identified bromethalin in the droppings and tissue, including brain tissue, of living and dead birds,” Ms. Yesney said in email.
“This time, it was a very long and painful journey and, it turns out, the cure is not within our control.”
Bromethalin poisoning has no cure
Although more than half of the afflicted parrots have managed to survive so far, many are left with permanent impairments that keeps most of them from returning to the “wild”.
“It appears that some birds can survive but are left with characteristic neurologic debilitation,” Dr. Van Sant pointed out in email. “This may include ataxia or leg weakness and incoordination. There are probably numerous variables, including the amount of bromethalin ingested and individual tolerances and how quickly they are recovered from the wild.”
There could also be species-level or individual metabolic differences that affect the parrots’ susceptibility.
“Some birds with neurologic debilitation, especially ataxia and a wobbly gait have stabilized and have been placed in experienced foster care homes,” Dr. Van Sant said. “Several of these birds have been doing well (as long as their special needs are met) for years.”
However, Dr. Van Sant and her collaborators are fairly certain that bromethalin poisoning survivors will decline over time.
“We have not seen any recover function.”
Complicating matters, these are urban parrots and thus, they can sustain a variety of traumas whether they are debilitated by bromethalin poisoning or not. For example, flying head-first into a window or a moving car can present symptoms that are similar to bromethalin poisoning.
“As there is no antemortem diagnostic test, we are left guessing which of the survivors were bromethalin poisoned and which sustained primary trauma,” Dr. Van Sant elaborated in email.
The source of bromethalin remains a mystery
“Bromethalin is the most commonly used rodenticide in the United States,” Ms. Yesney said in email. “The birds could be finding it (literally) almost anywhere — in back yards, in parks, along creeks, on rooftops.”
The concern is the parrots may be ingesting this poison from contaminated water or soil — and this means other animals are accessing it, too.
“We have no idea what wild species (birds and mammals) are being impacted and whether there can be accumulation in soil or run-off into water. We have no idea if birds ingesting poisoned rodents can become poisoned themselves. The poison can be hard to prove in mammals and extraordinarily difficult — as we found out — in birds.”
The study’s findings are worth the dedicated effort they required.
“The findings offer us an opportunity to assess the true risk of this rodenticide to pets and feral animals and to clarify the risk of potential soil and water contamination,” Dr. Van Sant explained in email.
“It is only because the poisoned birds were feral parrots that the condition was so thoroughly investigated,” Dr. Van Sant added.
Because of their celebrity, the plight of the Telegraph Hill parrots may well serve as a prominent warning to local health officials and medical providers that people — especially children — could also come into contact with this deadly poison.
Perhaps most troubling is the lack of a widely available and easily administered test to detect this commonly used poison.
“What I found the most surprising was that the United States and the State of California regulatory agencies allowed the widespread use of a toxic poison that is almost impossible to identify in animals that die from it,” Ms. Yesney said.
“The take away from this study is that we should be very careful about this commonly available rodenticide,” Dr. Van Sant said in email.
Or, I dunno, perhaps we shouldn’t use it at all.
According to Ms. Yesney, the University of Georgia researchers have indicated their desire to pursue a subsequent study to find out where the birds are finding this poison.
Fern Van Sant, Sayed M. Hassan, Drury Reavill, Rita McManamon, Elizabeth W. Howerth, Mauricio Seguel, Richard Bauer, Kathy M. Loftis, Christopher R. Gregory, Paula G. Ciembor, and Branson W. Ritchie (2019). Evidence of bromethalin toxicosis in feral San Francisco “Telegraph Hill” conures, PLoS ONE, 14(3):e0213248 | doi:10.1371/journal.pone.0213248
Originally published at Forbes on 27 March 2019.