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Deaths in Finches and Sparrows

As a result of finding several dead Greenfinches in his garden, Malcolm Watson went investigating, and passed on the following interesting article.

Introduction

Outbreaks of mortality in wild birds in gardens in the U.K. were first reported in the mid 1960s, when members of the general public began to put out bags of peanuts to feed the wild birds. In these first outbreaks most deaths were due to infection with the bacterium Salmonella typhimurium and occurred in greenfinches (Carduelis chloris) and house sparrows (Passer domesticus). Mortality incidents have continued, and since 1994 post mortem examinations have been carried out by the Veterinary Science Division of S.A.C. on over 200 finches or sparrows found dead in Scotland. The results from these investigations have shown that, in addition to Salmonella typhimurium, another bacterium is responsible for many of the deaths in wild birds, a strain of the bacterium Escherichia coli referred to as E. coli O86.

During these seven years a seasonal pattern has emerged. Salmonella typhimurium (often a particular type referred to S. typhimurium DT40) typically causes mortality in the months December to March, mostly in greenfinches and to a lesser extent in house sparrows. E. coli O86 usually causes mortality in the months March to June, especially in greenfinches and siskins (Carduelis spinus). Both bacteria have also caused deaths in goldfinches (Carduelis carduelis) and chaffinches (Fringilla coelebs), although in smaller numbers, and occasionally Salmonella spills over into other species such as the great tit (Parus major). Dead birds or sick birds are usually found in the vicinity of the bird feeders. If seen alive the birds appear fluffed up, reluctant to fly, appear to be breathing heavily and may look as if they are having difficulty in swallowing.

The post mortem examination of birds dying from Salmonella often reveals substantial yellow/orange areas of damage to internal organs such as the gullet, liver, spleen (an organ that tries to fight off diseases) and sometimes the lungs and lower part of the digestive tract. The damage to the gullet can be so severe that it causes a partial blockage, preventing food getting to the bird's stomach even if it continues to eat. The post mortem findings in birds dying from E. coli O86 are different. This bacterium doesn't cause such obvious damage to the internal organs but has the ability to produce toxins (poisons) that prevent the digestive tract from working properly. Birds dying from E. coli O86 typically have much food in the gullet but little further down the digestive tract. Confirmation of the cause of death requires the culture of the bacteria from the carcase on special laboratory media and identifying the bacteria that grow.

Deaths in the UK - 2001

Deaths in garden birds in the U.K. have become a regular occurrence each winter, and the year 2001 looks like being the same. On January 12th 2001 The Royal Society for the Protection of Birds reported unprecedented numbers of telephone calls from the public reporting sick and dead birds in gardens. Some dead birds have been examined by the Zoological Society of London, some by the Veterinary Science Division of SAC in Scotland, and the results confirm that Salmonella is again the major cause of the mortality. So far in 2001, salmonellosis has been confirmed by SAC in the greenfinch, chaffinch, goldfinch, house sparrow, and also the tree sparrow (Passer montanus), another bird whose population in the U.K. is in dramatic decline. Deaths in siskins in the second week of February 2001 were the result not of salmonellosis but of E coli O86 infection, which in past years has usually occurred later in the year, from March onwards.

Deaths in wild birds in North America and New Zealand

Deaths from salmonellosis have not been confined to sparrows and finches at bird tables in the U.K. Since 1988, many finches have been found dead around garden feeders in the United States and Canada, mostly pine siskins (Carduelis pinus) and common redpolls (Carduelis flammea), but also evening grosbeaks (Coccothraustes vespertinus), house sparrows, and American goldfinches (Carduelis tristis). As in the U.K. incidents, the type of Salmonella involved was Salmonella typhimurium phage type 40. Cases of salmonellosis were also reported in domestic cats that preyed on sick birds around bird feeders.

A different strain of Salmonella typhimurium described as S. typhimurium DT160 caused outbreaks of mortality in house sparrows in New Zealand in 1999/2000. At the same time there was evidence of spread of disease to humans (including one death), and to young farmed ducks and quail, dogs and cats, deer and horses. In one incident more than 400 dead birds were found at one location on one day. This strain of Salmonella typhimurium also caused a small outbreak of mortality in house sparrows in Central Newfoundland, Canada, in February/March 1999.

Why are the deaths occurring?

Although the mortality incidents in the U.K. usually occur at sites providing supplementary feeding for the wild birds, the food is not believed to be the initial source of the bacteria but rather the cause of the congregation of large flocks of birds in a small space. It is likely that some birds carry small numbers of Salmonella typhimurium and E. coli O86 in their intestines, and when the birds congregate at the bird tables and feeding stations a build up of these bacteria occurs, contaminating the food and water, the feeders and drinkers, and the surrounding environment. Under these conditions, the bacteria then have the chance to overwhelm the birds, damaging their intestines and causing their deaths.

Clearly prevention is very important, and is based on preventing a build up of these potentially lethal bacteria. Regular cleaning and disinfection of bird tables, feeders and drinkers will help, as will periodically moving the feeding sites. If the birds can be spread out by using several different feeding sites, so much the better. The areas beneath the feeders can also quickly become contaminated, and should be kept as clean as possible, with any uneaten food removed.

Declining populations

This greater awareness of the causes of mortality in finches comes at a time when the populations of some of the UK's wild birds are in decline, especially woodland species (down by 20% since the mid 1970s) and farmland species (down by 40% in the same period). In the report The State of the UK's Birds 1999, published by The Royal Society for the Protection of Birds and The British Trust for Ornithology, attention is drawn to the continued and alarming decline of once-common species such as the redpoll (down by 92% since the 1970s), the house sparrow (down by 58%) and the tree sparrow (down by 87%), three bird species known to be susceptible to salmonellosis. Indeed, the Report suggests that, such is the severity of the decline in house sparrow and redpoll numbers, they should be considered for inclusion on the Birds of Conservation Concern (BoCC) red list of endangered species.

Illness in humans

In addition to causing disease in finches, E. coli O86 and Salmonella typhimurium phage types 40 and 160 can also occasionally cause disease in humans, especially young babies. Rubber gloves should therefore be worn when cleaning bird tables or if the carcases of dead birds have to be handled, and hands must be thoroughly washed.

Further investigations

Much remains unknown about the occurrence of E. coli O86 and Salmonella typhimurium in healthy and sick wild birds of different species, and about the factors that allow these organisms to build up and cause disease. Two Trusts with an interest in wild bird conservation, The Dulverton Trust and The Game Conservancy Trust, are therefore funding a three-year study to look at the significance of these organisms in wild birds.

Are you finding dead garden birds?

Anybody finding dead garden birds can contact Tom Pennycott, Senior Veterinary Investigation Officer of the Avian Health Unit, S.A.C. Veterinary Science Division, Ayr at 01292 520318 for further information and advice. If a post mortem examination of small birds such as garden finches is to be carried out and the bodies are to be sent by Royal Mail, they must be securely packaged as follows:
  1. Wrap the body in sufficient absorbent material (e.g. kitchen roll) to absorb all possible leakage.
  2. Place the wrapped body in a leak-proof plastic bag (e.g. a freezer bag) and seal (e.g. with a metal or plastic tie, self-adhesive tape etc).
  3. Place the sealed bag in a strong clip-down container (e.g. a margarine container) or a strong cardboard box or polystyrene box, filling any empty space with absorbent material and sealing the container with self-adhesive tape.
  4. Details such as name, address and telephone number of sender, and any other additional relevant information such as number and species of birds found dead, should be enclosed in a separate sealed plastic bag and attached to the outside of the container.
  5. All the above should be secured in a padded bag or covered by strong brown paper.
  6. The outer cover should be labelled in bold capitals "PATHOLOGICAL SPECIMENS - FRAGILE - HANDLE WITH CARE" and addressed to Tom Pennycott, Avian Health Unit, SAC Veterinary Science Division, Auchincruive, Ayr, KA6 5AE. The sender's name and address should also be included on the outer cover.


Mr. Tom W. Pennycott
Senior Veterinary Investigation Officer, Avian Health Unit
SAC Veterinary Science Division
Auchincruive
Ayr KA6 5AE

February 12th 2001