New Scientist - 26.10.2019

26 October 2019 | New Scientist | 9

Zoology

Adam Vaughan

A BIRD that lives on mountains deep

in the Brazilian Amazon rainforest

has the loudest voice of any bird

species recorded so far.

Both songs of the male white

bellbird (Procnias albus) are loud,

but one is extremely so – at an

average of 116 decibels, it is on a

par with a piledriver and beats all

previously documented birds

(Current Biology, doi.org/dczb).

“It’s really, really distinctive and

it’s unusual because it’s very simple.

It’s one loud note, like a horn,” says

Jeffrey Podos at the University of

Massachusetts.

It isn’t just the volume that

is unusual, but also the fact that

the males sing so loudly so close

to the females. Most animals that

make very loud sounds – such

as howler monkeys – are trying to

communicate over long distances.

Joseph Tobias at Imperial College

London speculates that the close

proximity suggests the loudness

of the song is a sexual signal.

“If females detect the loudest

males from longer range and find

the loudest males most attractive

at close range, then sexual selection

would drive the evolution of

extremely loud songs,” he says.

Another possible explanation

is that, unlike most birds, the

species has great abs, with thick

and defined stomach muscles.

The loudness also seems to be

a by-product of the ecological niche

the birds have evolved to occupy:

their beaks open remarkably wide,

allowing them to grab the fruit they

eat, as well as make a loud song. ❚

World’s loudest

male bird bellows

at nearby females

You really don’t

want to perch

next to a male

white bellbird

ANSELMO D’AFFONSECA

Agriculture

Michael Le Page

GREENHOUSE gas emissions

would rise if all farms in

England and Wales went

organic. Though the emissions

of individual farms would go

down, much more food would

have to be imported, as the

amount they would produce

would decrease substantially.

“The key message from my

perspective is that you can’t

really have your cake and eat it,”

says Laurence Smith, now at the

Royal Agricultural University

in the UK, who was part of the

team that ran the numbers.

Smith is a proponent of organic

farming and says “there are a

lot of benefits to the organic

approach”, but his analysis

shows that organic farming

has downsides too.

Farming and changes in

land use, such as cutting down

forests, are responsible for a

third of all greenhouse gas

emissions. That means reducing

farming emissions and the land

needed for farming is required

to limit further global warming.

Smith and his colleagues

found that emissions per unit

of food are, on average, 20 per

cent lower for organic crops

and 4 per cent lower for organic

animal products. However,

organic yields per hectare are

also lower on average. For

wheat and barley, for instance,

yields are just half of those of

conventional farms. This means

1.5 times as much land would

be needed to grow the same

amount of these foods.

The estimated increase

in emissions varies greatly,

depending on where the

extra farmland comes from.

If only half comes from turning

grassland into farms, the

increase could be as low as 20 per

cent. If grassland that would

otherwise have been reforested

is turned into farmland,

emissions could nearly double.

“Organic farming has

this greenhouse gas problem,”

says team member Guy Kirk

at Cranfield University in the

UK. “You can’t ignore it.”

This doesn’t necessarily

mean people should stop eating

organic produce, says Smith.

Individuals might choose

organic food for other reasons,

such as to reduce their pesticide

exposure (though contrary to

popular belief, organic farmers

do use pesticides) or for the sake

of wildlife. And not all products

are equal, he says. Organic bread

is the worst, because wheat

yields are so much lower, but

for vegetables, the differences

are much smaller.

Going 100 per cent

organic could also harm global

biodiversity. The extra land

used for farming would mean

the land available solely for

wildlife would be smaller and

more fragmented (Nature

Communications, 10.1038/

s41467-019-12622-7).

Rob Percival at the Soil

Association, which certifies

organic farms in the UK,

thinks the analysis is “flawed”.

“The study assumes no

change in diet, which is clearly

untenable,” says Percival.

“Dietary change will benefit the

public’s health and free up land,

making an organic scenario

entirely feasible.”

There is no doubt that

reducing meat and dairy

consumption would reduce

emissions. Per kilogram,

emissions from animal-based

foods can be up to 50 times

those from plant foods, so the

kind of food we eat matters

more than whether it is

organic or produced locally,

says Hannah Ritchie at the

University of Oxford.

Smith says the best option

may be to use some organic

and conventional farming

methods in combination.  ❚

Going fully organic would

increase farm emissions

KELVIN MURRAY/GETTY IMAGES

Most organic foods

have smaller yields, so

they require more land

“ For wheat and barley,

organic yields per

hectare are half of those

of conventional farms”