RESEARCH LETTER No. 2.13

‘OF FISH AND FOWL’ II: BIRD MORTALITY IN LARGE SEVERE BUSHFIRES

In the aftermath of the ACT fires of January 2003, several reports of bird kills showing no apparent effects of flames were reported. For example, there were reports of deaths at Tidbinbilla (V. Raffaele, personal communication; Cary et al. 2003) and near to, or within, the suburbs of Holder (D. Jensen, personal communication), Chapman and Kambah (S. Katz, personal communication). The birds included lyrebirds, egrets, various cockatoo and parrot species plus a number of apparently less common smaller birds. What caused these deaths?

Bird deaths in fires were noted early in post-settlement Australia. Consider these examples:

There was a sound as of thunder, mingled with the crash of falling trees and the wild cries of legions of birds of all kinds; which fell scorched and blackened and dead to the ground” (Howitt 1856, referring to the 1851 fire in Victoria).

As they gazed around they could see the wild birds dropping dead from the forest trees ...” Boldrewood, R., 1899 p.120, referring to the 1851 fire in Victoria).

The roasted bodies of kangaroos and emus had to be pushed aside from the roads; birds had dropped from the trees killed by heat rather than fire; the track by the Barabool Hills to Melbourne was carpeted with dead magpies and parrots, and two lost children were found sheltering beneath a coverlet of stricken birds which had saved their lives. Birds flew desperately out to sea; a few found refuge on ships.” Kiddle 1967 referring to the 1851 fire in Victoria).

; “. Birds could be seen rising from the ground or leaving the trees in front of [the fire] only to be overpowered by the dense smoke and rising scorching heat. In all cases the birds fell exhausted into the flames.” (Hood, 1941, quoted by Woinarski and Recher1997).

In the past 40 years there have been at least 4 reports of dead birds being washed up on beaches after severe bushfires. After the fires in and around Hobart in 1967 Hemsley (1967) found 931 dead birds of 52 species washed up. Fires in 1972 and 1980 near Eden, NSW, elicited lists of 609 individuals of 41 species from Fox (1978) and 187 individuals of 27 species from C. Wheeler (personal communication) respectively. 2210 birds of 66 species were collected by Pescott (1983) after the Ash Wednesday fires of 1983 in Victoria. The most common birds in these lists were New Holland Honeyeaters and rosellas. The numbers of species found was a reflection of the number of individuals; the more individuals the more species. Were these birds just a sample of the population present at the time of the fire?

While the proportion of birds of a population lost as a result of fire are usually not known the fact that bird-species numbers may drop soon after fire may at first suggest high mortality but local and regional dispersal are also possible explanations for post-fire declines (see Hewish 1983, Lloyn 1997 and Woinarski and Recher for discussion and examples). Post fire predation and death by starvation (Cary et al. 2003) are other possibilities.

The following potential causes of direct death by fire are suggested:

(i) Flame contact: this cause seems unlikely in view of the observations of carcase condition of birds on the beach (Hemsley 1967) and by recent observations of dead birds in and near Canberra. Any bird falling into the fire could leave charred remains. It is difficult to evaluate the quotation of Hood (1941) above but the unwavering certainty and apparent comprehensiveness of the observation – “in all cases” - engenders caution in accepting it.

(ii) Thermal stress. Fire can force birds to fly from shady perches into heated air and perhaps sun; flying would add metabolic heat to the animal’s heat load. Bigger birds would have more difficulty in shedding unwanted heat than small birds so if this was a major cause the sample would be of mostly larger birds. Samples do appear to be dominated by larger birds but it is impossible to say whether this domination is just a reflection of the normal composition of the population. Also: larger birds may be more readily found than smaller birds;  andsmall birds, if washed onto beaches, may be more easily buried.

(iii) Smoke inhalation: this has not been assessed but may be expected to affect all birds, great and small, in the smoke column.

(iv) Muscle fatigue, disorientation and consequent drowning

(v) Combinations of the above.

Although the numbers of birds observed in the lists mentioned above are quite large, they represent only a small proportion of the populations likely to have been present in the areas burned. The fires were most unlikely to have caused any local extinction through mortality.

References cited

Boldrewood, R. (1899).Old Melbourne Memories. Macmillan and Co., New York.

Fox, A.M. (1978). The ’72 fire of Nadgee Nature Reserve. Parks and Wildlife (NSW) 2(2), 5-24.

Cary, A., Evans, M., Hann, P., Lintermans, M., MacDonald, T., Ormay, P., Sharp, S., Shorthouse, D. and Webb, N. (2003). Wildfires in the ACT 2003: Report on the Initial Impacts on Natural Ecosystems.EnvironmentACT Technical Report 17, 80p.

Hemsley, J.H. (1967). Bushfire – southeastern Tasmania 7th February, 1967. Draft Report.

Hewish, M (1983). The effect of a wildfire on birdlife in a eucalypt forest: a preliminary report on the Lerderderg Gorge seven weeks after the Wombat State Forest fire. Geelong Naturalist 20(1), 3-16.

Hood, J.B. (1941). Birds and bushfires. SA Ornithologist 15, 125-127.

Howitt, W (1856). Black Thursday. Household Words (London), May 10, pp.388-395.

Kiddle, M. (1967). Men of Yesterday. A Social History of the Western District of Victoria 1834-1890. Melbourne University Press, Melbourne.

Lloyn, R.H. (1997). Effects of an extensive wildfire on birds in far eastern Victoria. Pacific Conservation Biology 3, 221-234.

Pescott, T. (1983). Beach washed birds after the Ash Wednesday fire. Geelong Naturalist 20, 17-19.

Woinarski, J.C.Z. and Recher, H.F. (1997). Impact and response: a review of the effects of fire on the Australian avifauna. Pacific Conservation Biology 3, 183-205.

A. Malcolm Gill
22 January 2004