I've found this thread very interesting and all the contributors to the
discussion have made very valid points about the reasons for the decline in
insect abundance and the consequent decline in the abundance of insectivorous
Insecticides are no doubt having a big impact, but we must not lose sight of
other causes in the decline of insects and insectivores. Penny has already
mentioned the impacts of the recent Australian bushfires. Habitat clearance and
modification is another impact that we need to take into consideration, even if
it is partial habitat clearance. For instance, under-scrubbing, where canopy
trees are retained, can have a direct major impact on insect abundance and the
foraging habitat of insectivorous birds, but there are also indirect impacts.
There's a growing body of research that is now exploring these indirect
impacts, by investigating the relationships of organisms within and between the
trophic levels of an ecological community. Thinning of vegetation can alter
the soil chemistry by altering the organic content of the soil and variations
in soil moisture and soil temperatures. In turn, this can affect the microbial
communities that inhabit the soil. Soil microinvertebrates (e.g. mites, small
nematodes) that feed directly on the microbes, or benefit directly from the
release of nutrients from the breakdown of organic matter by the microbes, are
impacted by the changes in the microbial community. Soil macroinvertebrates
that are also dependent on the soil nutrients released by microbial action
(e.g. earthworms, myriapods, amphipods,) or which feed on microinvertebrates or
other macroinvertebrates (e.g. arachnids, ants, beetles, true bugs) are also
adversely impacted. But these impacts extend beyond the soil layers because
many adult insects that are found on tree trunks, logs and vegetation foliage
have larval stages that develop in the soil or in rotting wood and leaf litter
on the ground (e.g. large beetle grubs, cicadas). Fewer ground invertebrate
larvae means fewer adult invertebrates above-ground. This potentially results
in significantly less food for insectivorous vertebrates (reptiles, frogs,
birds and mammals). So altered soil chemistry, resulting from thinning of
habitat or increased nutrients (e.g. fertilisers) can have a cascading effects
on the higher trophic levels of an ecological community, which may be most
noticeable as a decreased abundance in bird populations.
Then there are the more complex interactions - altered soil chemistry and
moisture content can stress retained vegetation and make it more vulnerable to
insect, pathogenic and fungal attacks. This may temporarily increase the
abundance of some insects, which attack the tree foliage, which in turn causes
more leaves to drop to the ground. But if there is not the right microbial and
microinvertebrate balance in the soils and leaf litter, then it is going to
take a lot longer for that litter to break down and release nutrients into the
soil. A build-up in that litter (ground fuel) as a result of increased rate of
leaf-drop and reduced rate of leaf decay has the potential of making the
habitat more probe to wildfires. Increased increased, pathogenic and fungal
attacks can ultimately kill plants, which ultimately mean fewer insects if
there is no ongoing tree recruitment.
The above example is, admittedly, simplistic and does not take into account
more complex relationships between organisms, nor does it take into
consideration other larger impacts on insect and bird abundance, such as those
that have already been discussed in this thread. But I just wanted to
illustrate that the natural world is a complex one and we need to take into
account the indirect, as well as the direct ecological impacts, when discussing
insect and bird abundance. It also means that we might not have large numbers
of insectivorous birds in urban parkland or in streetscapes, especially if
those habitats are canopy trees surrounded by lawn or paving, because of the
absence, lower abundance or an imbalance of organisms in the lower trophic
levels. That open habitat structure favours aggressive species such as mynas,
miners and wattlebirds, which arguably chase smaller or more timid birds away.
But these urban habitats are also inadequate in providing enough food to
sustain insectivorous bird populations for the reasons I've described above.
From: Birding-Aus <> On Behalf Of Robin and
Sent: 20 May 2020 10:19 AM
To: rob morris <>
Subject: Re: [Birding-Aus] Insecticides
Quite frightening, but certainly facts we should all be aware of in the more
detail you have given.
> On 20 May 2020, at 6:31 AM, rob morris <> wrote:
> A couple of years ago I did some work for a legal related research defending
> a strawberry grower.
> The strawberry farm was upstream from a wetland where all the fish and most
> the birds had suddenly died. The owner was upset and had call the council.
> The local council tested the water and found 7 pesticides over allowable
> environmental limits.
> I sampled water across the site and the lab results confirmed the local
> councils results - a very close match. One organophosphate you can use in
> Auz, (banned in Europe and the USA) was over 1000x the allowable
> environmental level). We also analysed the spraying records.
> The results didn’t help defend the accused and we were asked not to send in
> the report.
> What amazed me though was in a strawberry growing season the crop had over
> 250 chemicals sprayed on to them. About 1/2 were chemical fertilisers etc and
> the other 1/2 were fungicides, herbicides, insecticides, general pesticides.
> So when you buy those little punnets of strawberries on the cheap in Coles
> and Woolies etc. be aware of the process to get them to you. It would be
> similar for a lot of fruit and veg I’m told!
> Sent from my iPhone
>> On 19 May 2020, at 12:06, Penny Brockman <> wrote:
>> Our rural town of Gloucester has ever since I moved here sprayed in town and
>> along streets to kill weeds leaving behind a depressing dead mess that
>> eventually is blown away or squashed into dust by vehicles. At the same time
>> we still have a very healthy population of House Sparrows. There are 4 sites
>> known to me where they breed one close to my house. So far so good.
>> However no doubt combined with herbicide and insecticide spraying , the
>> disastrous effects of the fires which brought heavy smoke to the area
>> December January has resulted in a serious decline here in small
>> insectivorous woodland birds. I no longer count more than a couple of E
>> Spinebills in the garden, Red/browed Finches, whistlers, thornbills, small
>> honeyeaters were also seriously reduced in numbers and with winter coming
>> on, we won’t see any change until spring. Along the river banks where native
>> vegetation remains things are a bit better. These areas were refuges even
>> when water levels were reduced to a few puddles of revolting green gunge.
>> Many birds took refuge at the coast in unburnt areas. They didn’t return
>> when the rains came mid January.
>> The other notable effect of the extreme heat was the absence of flies-
>> changed abruptly after the rains when they erupted. I’m told due partly to
>> absence of dung beetles.
>> Penny Brockman
>>> On Tue, 19 May 2020, at 4:07 AM, Michael Hunter wrote:
>>> After an ornithologically sterile month traversing California, a
>>> creeping realisation that Mulgoa Valley, once seething with small
>>> birds now has far fewer, ditto Avoca on the NSW Central Coast, the
>>> penny dropped.
>>> INSECTICIDES. are wiping out the base of the food chain in built
>>> up and semi rural areas.
>>> Not just for small birds, but all the way up to raptors like
>>> Black shouldered Kites and falcons which include insects directly,
>>> and indirectly via small reptiles which are largely insectivorous.
>>> Honeyeaters eat insects in flowers as well as their nectar.
>>> A very obvious example has been the demise of House Sparrows
>>> worldwide, although granivorous their young need animal protein, in
>>> the form of insects, to develop. Those insects have largely gone due
>>> to insecticides, House Sparrow sightings are now rare. My last
>>> single sighting was in Bunnings Gosford Nursery. ? Significance ?
>>> Most Reptiles, most small Mammals, most Amphibians and most
>>> Fish need insects.
>>> How many Councils spray entire suburbs for Flies and
>>> Mosquitos, unwittingly killing thousands of birds and reptiles.
>>> A giant problem. Any suggestions re a longterm solution.?
>>> "Bring Back the Birds. Ban inorganic and long lasting Insecticides "
>>> Hoping that this starts a longterm campaigns
>>> Much more to come.
>>> Sent from my iPhone
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