A myriad of new discoveries about birds were made in the year 2019 which unveiled the emerging struggles faced by our feathered friends in adapting to a warming world, while also shinning new light on the fields of behavioral science, genetics, and avionics.
Revelations that bird species across the world are shrinking in size, and a major finding that the North American continent has lost a quarter of its avians in the last 50 years, were among some of the biggest ornithology discoveries made this year.
"The missing of about three billion birds since 1970 indicates the massive decline of biodiversity all over the world," Asad Rahmani, former director of the Bombay Natural History Society told PTI.
Amidst these worrying discoveries, there were also some bird studies that offered useful insights for novel bio-mimetic aviation technology that mimics the behaviour of the birds.
Engineers at the University of Pennsylvania in the US developed an electronic circuit mimicking how barn owls determine the direction of their prey.
The researchers found that the owl brain's circuitry works in a specialised way to calculate direction based on when the signals from its two ears coincide, which helped develop a similar-working bio-mimetic circuit.
The year also saw new research offering clues about the evolution of birds.
In a first-of-its kind study, published in the journal Evolution, researchers measured beak shapes of numerous modern birds, and assessed how the part is used by different species to eat various foods.
The study found that many birds with similarly shaped beaks forage in entirely different ways, and on varied food types, showing that the link between beak shapes and feeding ecology in birds are more complex than previously thought.
In September, scientists discovered fossils of one of the world's oldest bird species that lived about 62 million years ago, soon after the dinosaurs became extinct.
According to the study, the newly-discovered Protodontopteryx ruthae was only the size of an average gull, whereas its descendants were some of the biggest birds to have ever flown, soaring with wingspans of more than five metres.
New understanding of the social life of many birds also emerged in 2019 -- from secret mating rituals of some avians to 'building blocks' of their communication, which helped unlock mysteries of human language.
In a study published in the journal PNAS in September, researchers analysed the calls of the chestnut-crowned babbler -- a highly social bird from Australia -- and discovered that their vocalisations, like human languages, can be broken down into distinct meaningless sounds.
"To our knowledge, this is the first time that the meaning-generating building blocks of a non-human communication system has been experimentally identified," study co-author Simon Townsend of the University of Warwick in the UK said in a statement.
Another research, assessing the mating calls of the bellbird found that they have the loudest bird calls yet documented in the world -- packing more decibels than the screams of howler monkeys and the bellows of bison.
In October, scientists revealed that bacteria growing in the oil-secreting preen glands of birds are important for them to produce odour and attract mates.
Altering these microbes, the study published in the Journal of Experimental Biology said, could negatively impact the ability of birds to communicate with others of its species, or find a mate.
In another major study, scientists in Japan discovered that the species-specific tunes sung by songbirds depend on genes in their brain's song nucleus -- the region responsible for vocal learning and production.
When the researchers treated adult zebra finches with drugs that over-activated some parts of the song nucleus, the birds sang unusual songs with different patterns compared to their normal tunes.
The year also witnessed a series of studies describing a worrying tale of dwindling bird populations across the world -- trends which may extend into the future.
One such finding revealed that bird population in the US and Canada declined by nearly a third since 1970.
According to the study, published in the journal Science, there were probably around 10.1 billion avians in the two North American countries nearly half a century ago, with this number currently falling by 29 per cent to about 7.2 billion birds.
It cited earlier research that domestic cats could be killing nearly 2.6 billion birds each year in the US and Canada, with nearly 840 million lost to window and car collisions.
"We came to know about missing birds in the US as they have a good monitoring system in place. While in India, we know there has been a massive decline of common birds, we do not have monitoring data," Rahmani said.
Another major study was the discovery that global warming may be causing many birds to shrink in size, while increasing their wingspans.
The University of Michigan researchers in the US found that, from 1978 through 2016, body size decreased in all 52 bird species they assessed.
"We had good reason to expect that increasing temperatures would lead to reductions in body size, based on previous studies," said study lead author Brian Weeks.
"The paper on reduction of bird size and bills indicates that nature has tremendous adaptability and some species may adapt to climate-change, but overall climate change will have negative impact on most species," Rahmani said.
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