The biology of bird management

The biology and behavioural characteristics of birds impact upon pest bird management in numerous ways. It firstly helps us understand why it is that some birds are able to become such pest species, and secondly aids in the development of ways to limit these birds’ ability to become a nuisance. The biology and behaviour of birds determines how bird management is conducted. Birds share several characteristics with pest insects, including their ability to fly and hence disperse over large areas, their relatively small size, their ability to adapt human constructions to meet their needs, their high fecundity and the consequential speed with which a small number of birds can become a pest flock.

Understanding the biology and behaviour of birds greatly assists those individuals and companies involved in practicing bird management. Pest bird management is approached through an examination of the relationship between the bird and the site in question. The primary question is that of how committed are the birds to that site? This concept in the pest control industry is referred to as bird pressure (Riddell, undated), and it varies between a very high level, to moderate and low commitment, depending on what the site provides for the birds. The greatest level is that of a protected nesting or roosting location. Medium commitment is often exhibited by birds to a site from which they can obtain food and/or water; and a low level of commitment, referred to as light pressure, is seen in exposed areas that are used as gathering places.

BIRD BIOLOGY and BEHAVIOUR

An indication of the characteristics of birds that make them a pest is undertaken below in a summary of various bird species. It is worth noting that most birds that are categorised as pests are introduced species. The below table is a listing of exotic pest bird species and the level of problem they pose in Australia.

Table 1: Introduced species posing a pest problem in Australia

Bomford and Hart (2000)

More than 20 bird species have established permanent wild populations on the Australian mainland. Whilst some were introduced on purpose (Cattle egret Ardeola ibis introduced to control cattle tick in 1933 (Cayley, 1984)), others such as the indian mynah were released illegally (Bomford and Hart, 2000). Exotic species that have established themselves well in Australia have generally been able to do so due to the similarity between Australia’s and their native climate, their high reproductive rate, and a generalist diet (Bomford, 1991; Duncan, Bomford, Forsyth and Conibear, 2001). Those that are classified as urban pest birds exhibit an ability to live successfully in a human disturbed environment. Indeed habitat modification may have precipitated or further encouraged the establishment or dispersal of such species, many of which have a history of establishing exotic populations outside of their native environment (Newsome and Nobel, 1986). These species commonly have an ability to out-compete many native species for food and water or shelter.

PEST BIRD SPECIES

Of the estimated 850 species of birds occurring in Australia, 70 are thought to be alien species (Pimentel et al, 2000). Hence, and notwithstanding the impact of exotic pest bird species, it is unsurprising that there are a number of native Australian species that also pose a problem and require control. Introduced pest bird species are likely to cause at lease $10 million in agricultural losses in Australia per annum, and governments and landholders are estimated to spend in excess of $3 million on bird control (Bomford and Hart, 2000). Include in this the damage done by native Australian pest bird species in the food production and rural industries and the figure more than doubles. In many cases the law in Australia actually encourages land holders to control agricultural pests and government conservation agencies are also charged with facilitating this dictate. The primary pest bird species (introduced and native) are considered below.

Pigeons (Columba livia)

Pigeons have totally adapted their lives to a human created urban environment. Nesting in small communities, pigeons often emerge from their nesting and roosting place to join a flock of hundreds of birds. They thus have a very heavy impact on suburban streetscapes, industrial sites, grain storage facilities, ports and food processing plants. Their impact on food safety is a critical issue and the food processing and services industry are reacting favourably to the need for control.

European Starling (Sturnus vulgaris)

These are both an urban and rural pest, causing high levels of damage to fruit crops and winter-sown cereals (Bomford, 1992). They also compete with and displace native birds for nesting hollows (Agriculture Western Australia, 1998). They are comfortable nesting in roof and ceiling cavities and cause significant damage to roof sarking and insulation as well as create a significant mess and health issue when nesting in confined roof and cavity spaces.

House Sparrow (Passer domesticus)

Like starlings, the house sparrow has both a rural and urban impact, defacing buildings as well as spoiling fruit, vegetable, grain and oilseed crops (Long, 1981; Bomford, 1992). They may also assist in the spread of diseases such as salmonella and tuberculosis (Weber, 1979). They are aggressive and compete with native birds for nesting sites and food. Their prolific breeding and early sexual maturity means that a single pair of birds can multiply to become a problem flock in a short space of time.

Gulls (Larus sp.)

The primary gull in Australia is the silver gull (Larus novaehollandiae), a significantly smaller species than the dominant pest gull species in north America or western Europe (the pacific gull). Traditionally restricted in range to coastal areas, the silver gull now inhabits inland, rural and regional towns. The silver gull inhabits and nests in the waste management facilities of many townships throughout coastal and inland Australia.

Indian Myna (Acridotheres tristis)

Indian mynas compete strongly with native birds such as the crimson rosella (Pell and Tidemann, 1996). They nest in hollows and building cavities and are carriers of bird mites. In Hawaii the bird is known as a major means of spread of harmful weeds in particular Lantana camara (Pimentel et al, 2000). Originally introduced into Melbourne, the indian myna was redistributed to the Townsville area as a means of controlling grasshoppers and cane beetles. It is now listed on the top 100 of the world’s worst invasive alien species (ISSG, 2004).

Cockatoos and parrot species (Various sp.)

There is quite a range in the intelligence of birds, with cockatoos and parrots towards the top. These species vary in their behaviours, diet and other characteristics significantly from one to another. There are over 50 native species of parrot living in Australia. Many of these are considered pest species in rural and grain areas due to their consumption of commercially intended produce. Some have also become pest species in urban areas. This occurs in particular in locations where flocks of cockatoos have easy access to a food source, spending the remainder of their day not foraging for food but rather entertaining themselves through acts that are destructive to property. Consequently the management practices required for these birds differ not only from other birds but also from species to species within the parrot family.

Australian White Ibis (Threskionis aethiopica)

Traditionally nesting in reeds and low vegetation in inland aquatic areas, the Australian white ibis has emerged as one of the most serious native pest bird species of the present era. This species now congregates in the thousands on the Australian east coast in landfill, parks and gardens. The presence of the Salmonella bacteria in this species’ scats, and its preference for congregating in city and suburban parks and gardens where members of the public meet to enjoy picnics and commercially available food, makes this situation a serious cause for concern. Their large size, as well as the associated smell and unsightly impact means that they have a significant effect on urban waterways where it is unpleasant at best when large infestations occur.

Additional pest species include swallows, magpies, blackbirds, crows, ravens and others depending on location and infestation size.

SPECIES and MANAGEMENT CHOICES

Different species require different responses to a pest problem, due primarily to their biological variations, different habits and needs, different behavioural aspects, location in an urban or rural landscape and varied levels of intelligence.

- Some birds are much more prolific breeders than are others. Highly fecund species such as sparrows, starlings and indian mynas need to be more closely monitored and control measures taken earlier than with some other slower breeding species.

- Bird netting and spikes used for pigeons may not be particularly useful with birds that are much smaller. A smaller meshed netting, electric ledge deterrents or a different approach may need to be taken.

- Birds such as swallows that build mud nests against the underside of an eve will require a different approach than will a bird that builds a nest on a ledge or flat surface.

- An inundation of Australian white ibis’s can not be handled using traditional pest management barrier techniques. Instead removal of eggs and nests is the primary means of controlling these populations. This is because of their communal nesting behaviour in large trees and palms in urban parks and gardens, thus making it difficult to exclude them from their natural environment.

There is a need to look not only at an individual species’ characteristics but also at the behaviour of each flock. This is because the bird pressure can vary due to availability of shelter, food and water, as well as the length of time that the flock has inhabited an area.

BIRDS AND HUMAN DISEASE

The term zoonotic disease refers to any disease that a human can acquire from an animal. Bird biology is important not only in regard to understanding the management of the pest species, but also in relation to knowing why birds can be not only a pest but also a hazard to human and animal health. This assists in understanding the reasons pest birds need to be managed, and recognising the precautions that need to be taken in the handling of pest bird sites. More than 60 transmissible human diseases are associated with birds. Diseases may be spread by birds in several ways including through scats, insect vector transmission or direct contamination of human food or drinking water by birds.

Bird scats and debris

Bird droppings may be the cause of diseases, as well as resulting in considerable damage to property due to their composition of uric acid. In addition yeasts which live in bird feces also excrete acids. Diseases caused by micro-organisms found in droppings come in the form of fungal, bacterial, viral and protozoal diseases.

Fungal diseases

Fungi are classified as neither plant nor animal but instead form a kingdom of their own. Fungi feed by absorbing nutrients from organic material and secrete acids and enzymes. Different fungi have evolved to live on plants, animals and some even insects. The effects of fungal disease on humans may range from a mild condition to deadly (http://www.fungalresearchtrust.org). The primary fungal diseases related to birds are:

– Histoplasmosis - respiratory disease that can produce a tuberculosis-like illness as well as having ocular side effects. Birds, due most likely to their high body temperature, do not carry the disease. Instead, fungal spores (Histoplasma capsulatum) survive in soil, in particular that with a high nitrogen content, which is enriched by feces. Hence the fungus is of most concern in soil under roosts where bird droppings and feathers providing a suitable site for the fungus already resident in the soil to grow. Illness is caused by inhalation of the spores when the soil or feces is disturbed and becomes airborne.

– Cryptococcosis – is a yeast found in the digestive tract of pigeons and starlings. In humans it affects the lungs and nervous system. It is found mainly in long term roost sites.

– Psittacosis – (Chlamydia psittaci) can be contracted from birds again usually due to the inhalation of dry droppings. This causes fever, chills, headaches, coughs, with severe symptoms leading to inflammation of the heart, liver and nervous system. It has been linked to pest bird species but also pet birds such as cockatiels.

– Aspergillosis – a respiratory disease caused by inhallation of aspergillus, a group of moulds (filamentous fungi) that causes illness primarily in immuno-compromised people. It may occur in the lungs or the sinuses and can take several forms ranging from a mild allergy to life-threatening infections. Symptoms of aspergillus disease in the lungs include weight loss, chronic cough, feeling rundown and tired and coughing of blood in up to 50-80% of affected people. Similarly in the sinuses symptoms are often a simple allergy reaction. However, in part because there is no good single diagnostic test, many people with damaged or impaired immune systems die from invasive aspergillosis. Can show up as yellow to greenish urates in droppings.

– Candidiasis – yeast or fungal infection spread primarily by pigeons. It affects the skin, mouth, respiratory system, intestines, urogenital tract and vagina. It can be serious causing a deep candida infection in a small number of people.

Bacterial diseases

Bacteria consist of only a single cell, and fall into a category of life called the Prokaryotes whose DNA is not enclosed in a nucleus. Though there are many beneficial forms of bacteria, some may be harmful to humans.

– Salmonellosis – there are over 2,000 different species of Salmonella responsible for a variety of ailments. Food Poisoning (from Salmonella enteritidis, typhimurium) is a food borne illnesses. Salmonella bacteria live in the intestines of birds and other animals. It is found in the bird dropping of species including pigeons, starlings and sparrows. It may be spread when a diseased bird directly defecates into a human food or water source, or may be carried in dust from droppings or passed on hands which have touched a surface containing the bacteria. Symptoms include fever, abdominal cramps and diarrhoea.

– Chlamydiosis (Ornithosis or Chlamydiophila psittaci) – also known as Parrot fever it is a flu-type illness, with symptoms of cough, fever, nausea and muscle pain. Chest X-rays will show extensive pneumonia. Active roosts present greatest risk, and it is widespread in parrots and pigeon populations, though seabirds may also be carriers. Infection occurs through the inhalation of C. psittaci bacteria that are present in dried bird droppings, feather dust or other secretions of infected birds. Person-to-person spread of psittacosis is very unlikely (http://health.utah.gov/els/epidemiology/epifacts).

– E. coli 0157:H7 - Currently, there are four recognised classes of enterovirulent E. coli (collectively referred to as the EEC group) that cause gastroenteritis in humans. Among these is the enterohemorrhagic (EHEC) strain designated E. coli 0157:H7, that produces large quantities of one or more related, potent toxins that cause severe damage to the lining of the intestine, and in its acute form results in hemorrhagic colitis disease.

Viral diseases

– Newcastle disease - virus can survive outside of the host and in dead birds (sparrows). Exotic Newcastle disease (END) is a contagious and fatal viral disease caused by the paramyxovirus and affects all species of birds. It is spread through infected droppings and respiratory discharge between birds. Though primarily a disease of poultry, inapparent infections and carrier states can occur in other bird species. Contamination can also occur through contact in the environment including food, water, equipment, and human clothing.

– Cryptococcocal Meningitis has been reported to have been contracted by workers exposed to bird droppings, leading to chronic inflammation of the brain.

Protozoal and rickettsial diseases

– Q fever (Coxiella burnetii) forms environmentally resistant spores that are spread through the inhalation of contaminated dust, although can also be transmitted via the bite of various species of ticks. It can result in primary Q Fever which causes death in less than 1% of untreated cases. Chronic Q fever may develop between 1 and 20 years after initial illness or exposure. This is much more serious than primary Q fever having a 10-60% mortality rate.

Introduction of parasites and insects

Parasites transfer disease having sucked the blood containing the germ of an infected animal. Parasites inject some of their saliva into the host when feeding and hence when the parasite bites its next victim it passes along the germ to the new victim. Over forty types of parasites live either on birds, in their nests or in the places they roost. While many of these are household pests, only a selection actually carry and transmit diseases to humans. Most are nonetheless undesirable additions to a home.

Parasites and insects associated with birds include:

• Blood feeders – fleas, lice, bugs and mites
• Bed bugs (Cimex lectularius) are carried in a variety of birds including pigeons, starlings and house sparrows. They may consume up to five times their own weight in blood.
• Chicken mites (Dermanyssus gallinae) are known carriers of encephalitis. Though they live on blood drawn from birds, they may also feed on humans.
• Feather eaters – mealworms, spider beetles, carpet beetles, clothes moths
• Yellow mealworm (Tenebrio molitor) live in pigeon nests but have been found on a variety of birds including starlings and house sparrows. They again live on bird blood but have been known to attack humans.
• Meat eaters – various carrion flies & beetles
• Wood eaters – furniture beetles, death watch beetles (anon, undated)

Paradoxically, parasites and insects can be aggravated when bird control products are installed. Unless the parasites are exterminated when the birds are excluded from a site, the mites, fleas and ticks will seek a new host, often the human inhabitants. Therefore, a proper bird control project will always include parasite extermination.

In addition to these insect pests the presence of birds may actually encourage rodent pests to enter a premises in order to forage for eggs. This then leads also to the introduction of rodent associated parasites to the area.

Vector transmission

Some insects interact with both birds and human. This, in some specific circumstances, may result in the transmission of diseases from birds to humans. For example, mosquitos have been known to be a vector for west nile fever carried by crows, a particularly dangerous disease to elderly or other immuno-compromised people. The danger of vector transmission is increased where the carrier bird is a highly migratory species and able to travel from areas of high disease occurrence to previously uninfected regions.

Encephalitis is a viral disease caused by the paramyxovirus. It is an inflammation of the nervous system that can cause drowsiness, headaches and fever, extreme cases result in paralysis, coma or death. It is spread primarily by mosquitos which have fed on infected house sparrows, pigeons and house finches carrying the disease. Several strains of encephalitis exist including St Louis encephalitis, eastern equine encephalitis and west nile virus.

Particular attention has focused in recent years on the west nile virus. Caused by the arbovirus and spread mainly by the mosquito Culex pipiens. Occurrence of the virus spread to more than 10 US states in 2001 mainly by bird movement. In New York concerns resulted in the spraying of pesticides over hundreds of acres including Central Park. Several confirmed deaths have resulted from the illness.

WHAT DOES BIRD BIOLOGY TEACH US FOR MANAGEMENT?

Understanding your Pest Bird

Understanding the difference in bird biology and behaviour between species can not only help identify what birds are present but also the best way to handle pest bird situations. In addition it is important to consider what indirect impact on non-target species a certain course of action may lead to. It is for this reason that in many areas bird baiting is either not the first tool of choice or in many scenarios may be unacceptable and potentially illegal. It needs to be acknowledged that non-target birds, even if not endangered, are likely to be Australian native species and afforded some level of protection by law. This protection will also carry over to the nests and eggs of such species. This is not to say that Australian native species can not also be pest bird species.

Bird Scat Biology

Cleaning of bird scats is an important aspect of bird management. This is of particular importance because of the ability of bird feces to transmit diseases over long distances if airborne. One early documented case (Dean et al, 1978) reported that the shovelling of excessive bird droppings on a building led to the contraction through the air conditioning system of Histoplasmosis by over 50% of the building occupants. As such methods should be applied to reduce dust during the cleaning of bird scats off a building. These include water sprays and chemical sterilisation agents. Although these will not kill the spores they may kill bacteria and viruses. Also available for use are enzymes to biodegrade fatty acids of feces in drains or similar situations. Other precautions which should be taken include the use of respirators by pest bird management professionals.

Bird Scaring Devices

Birds are poor auditory communicators and therefore various bird scaring devices have offered limited success in most situations. In areas of high bird pressure where there is abundant food, water and shelter available, the level of commitment of birds to reclaim their territory is far too great. Limited success with scaring devices has worked in situations with waterfowl where the devices have been used over extended (6 month) periods, and in conjunction with other techniques (such as physical disturbance) (Whitford, 2003). Acoustic harassment devices via the use of species specific distress calls have had some but limited success on species with higher reliance on communication for social interaction.

Exclusion Devices

Sophisticated cable and netting systems are now readily available in the Australian market for the exclusion of pest bird from building structures. Stainless steel fittings are used to suspend stainless steel tensioned cable around the interior or exterior of pest bird infested facilities. Polyethylene professional urban knotted netting is attached to the cable system using specialised net rings and installation tools. Care should be exercised when selecting the type of net so as to ensure that it is not only UV stable but also of the correct mesh size for the particular bird species. Included is an example of the types of products available and outline of their use.

Physical Deterrants

Various forms of physical deterrents are now available to bird management professionals. These include ledge deterrents (post and wire systems, stainless steel coils, and spikes), and platform deterrents. In this latter category falls the unique Daddi Long Legs, that is widely used on streetlights, rooftops and air conditioning units. Designed for pigeons and seagulls, most if not all of the physical deterrents are not designed for smaller birds such as sparrows and swallows. These products can actually offer a suitable nesting site and protection from predators for such birds. Included is an example of the types of products available and outline of their use.

Electric Ledge Deterrents

Devices designed to send a direct current along an electric track system in order to repel birds from a popular location is a relatively new mechanism in Australia. These systems have however been used in the United States for over a decade. It is modelled on the same premise as that of electric fences for cows or other domesticated grazing animals. Significant improvements in the design of electric ledge deterrents and the use of solar power ensure that these are likely to be a much more accessible tool for Australian bird managers.

Other bird management mechanisms such as the use of avicides (poison), trapping, taste deterrents, visual deterrents, relocation and shooting have all been used to reduce pest bird populations. These have met with mixed levels of success depending on bird species, bird pressure, and population numbers. In most cases favourable conditions as well as the availability of food, water and shelter as well as birds’ reproductive rates ensures that the current or a new bird population continues. However, these techniques have been used as a support mechanism to more traditional bird management measures with some success.

References

Ainsworth, G., and Austwick, F., “Mould Toxicoses and Poisonous Fungi ”in Fungal Diseases of Animals (London, 1959).
anon, “Why Effective bird Control is Important”, Bird-X www.bird-x.com, undated
Bomford, M., Importing and Keeping Exotic Vertebrates in Australia: Criteria for the Assessment of Risk: (Bureau of Rural Resources, Canberra, 1991).
Bomford, M., Bird Pest Impact and Research in Australia: A Survey and Bibliography (Working paper 3/92) (Bureau of Rural Resources, Canberra, 1992).
Bomford, M. and Hart, Q., "Non-Indigenous Vertebrates in Australia", in Pimentel, D. (ed), Biological Invasions: Economic and Environmental Costs of Alien Plant, Animal and Microbe Species (CRC Press, New York, 2000) pp 25-44.
Cayley, N., What Bird is That? (Angus and Robertson, Sydney, 1984).
Dean, A., Bates, J., Sorrels, C., Sorrels, T., Germany, W., Ajello, L., Kaufman, L., McGrew, C. and Fitts, A., "An Outbreak of Histoplasmosis at an Arkansas Courthouse with Five Cases of Probable Reinfection" (1978) 108 American Journal of Epidemiology 36-46.
Duncan, R., Bomford, M., Forsyth, D. and Conibear, L., "High Predictability in Introduced Outcomes and the Geographical Range Size of Introduced Australian Birds: A Role for Climate" (2001) 70 Journal of Animal Ecology 621-632.
Long, J., Introduced Birds of the World (Reed Books, Sydney, 1981).
McCarthy, P., "Bird Management in Grain Storage Facilities", paper presented at Australian Postharvest Technical Conference (CSIRO and GRDC, Canberra, 2003).
Newsome, A. and Nobel, I., "Ecological and Physiological Characters of Invading Species", in R, G. and J, B. (ed), Ecology of Biological Invasions: An Australian Perspective (Australian Academy of Science, Canberra, 1986) pp 1-20.
Pell, A. and Tidemann, C., "The Impact of Two Exotic Hollow-Nesting Birds on Two Native Parrots in Savanna and Woodland in Eastern Australia" (1996) 79 Biological Conservation 145-153.
Pimentel, D., McNair, S., Janecka, J., Wightman, J., Simmonds, C., O'Connell, C., Wong, E., Russel, L., Zern, J., Aquino, T. and Tsomondo, T., "Economic and Environmental Threats of Alien Plant, Animal and Microbe Invasions" (2000) 84 Agriculture, Ecosystems and Environment 1-20.
Pimentel, D., "Environmental and Economic Costs of Nonindigenous Species in the United States" (2000) 50 BioScience 53-65.
Per comm.. Cameron Riddell, President, Bird Barrier America Inc, undated.
U.S. Food & Drug Administration, Center for Food Safety & Applied Nutrition, Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook (Washington DC, undated)
Weber, W., Health Hazards from Pigeons, Starlings and English Sparrows (Thompson Publications, Frenso, CA, 1979).
Whitford, P., "Use of Alarm/Alert Call playback and human Harassment to End Canada Goose Problems at an Ohio Business Park", paper presented at Proceedings of the 10th Wildlife Damage Control Conference, 9 April 2003).

Websites

Avian Web, http://www.avianweb.com/diseases.htm
Avian Biotech International, http://www.avianbiotech.co.uk
Agriculture Western Australia – 1998, http://www.agric.wa.gov.au/agency/pubns/infonote/infonotes/starling.html
Bird Barrier America, http://www.birdbarrier.com
Fungal Research Trust, http://www.fungalresearchtrust.org/
Global Invasive Species Database, http://www.issg.org/database/species
Purdue University, http://www.entm.purdue.edu.entomology/E-series/index.html
Texas Department of State Health Services, http://www.tdh.state.tx.us/ideas/avian_flu/faqs/
Utah Health Department, http://health.utah.gov/els/epidemiology/epifacts
Virtual Bacteria Museum, http://www.bacteriamuseum.org/main1.shtml

Fact Sheets on various pest bird species are available on request from the authors – ph 1300 66 56 57 or email info@pestIT.com

Acknowldegements

We would like to thank the following people for information provided: Cameron Riddell (Bird Barrier), Paul Hoyes (Killgerm), Richard Davies (NSW NPWS), Peter Lamond (Rentokil Initial), Alison James (Bird-X).

Origin: Pest IT Pty. Ltd.