Anybody who strolls down the leafy streets of Jerusalem’s Beit Hakerem neighborhood near my home has become used to hearing strange calls of birds in the tall trees and seeing green parakeets flitting from one to another. Parakeets living in 98-year-old Beit Hakerem?
These non-native invaders are firmly ensconced in the neighborhood, the descendants of pets that escaped or were released from cages years ago. Such scenes occur in many places around Israel, and they are not good news from native species. In fact, species are declining worldwide, but while some are becoming threatened, a few others thrive under novel environmental conditions.
Conservation scientists Dr. Agathe Colléony and Assistant Prof. Assaf Shwartz of the Technion-Israel Institute of Technology in Haifa recently investigated trends of common bird populations across Israel over the last 15 years. The study found that 75% of the most common bird species in Israel have been in decline for the past 15 years, while populations of three non-native invasive alien bird species have been exploding at rates between 250% to 843%.
They found, to their consternation, that invasive alien bird species are thriving and native ones are largely declining. “It is important to set appropriate management strategies to halt or mitigate the spread of non-native birds, particularly the common myna,” said Colléony.
Among the bird species rapidly declining are the house sparrow (Passer domesticus), which has declined by 28%, and the white-spectacled bulbul (Pycnonotus xanthopygos), whose population has dropped by 45%).
“It is worrisome that the species we grew up with are now disappearing,” said Shwartz of the Technion’s Faculty of Architecture and Town Planning. “I am afraid that soon my children won’t be able to see and hear and interact with the sparrow, the bulbul, and the Palestine sunbird, which used to be very widespread across Israel.”
Almost two decades ago, “we started studying the effect of invasive alien birds on local ones. We found that the common mynas outcompete some local cavity nester species such as the house sparrow and also demonstrated aggressive behaviors towards other native bird species,” said Shwartz.
This study was just published in Biological Conservation under the title “When the winners are the losers: Invasive alien bird species outcompete the native winners in the biotic homogenization process.”
The authors found that three invasive bird species that were growingly spreading over the country, the common myna (Acridotheres tristis) and two species of parakeets (Psittacula krameria et Myiopsitta monachus) are flourishing while several native species are declining.
“Unfortunately, this study shows that our predictions are now becoming the reality in Israel,” Shwartz bemoaned.
Land use changes and biological invasion are the main drivers of this ‘biotic homogenization’ (BH) that increasingly occurs in human-dominated landscapes. The native common species of animals that were considered “winners” in this process are now “losers.” The ultimate “winners” have been non-native species.
Among birds, several groups of species have been identified as “winners” in this process (invasive and native urban specialists and generalist species). Yet, as populations continue to grow, competition can appear between those groups and it is not yet clear who are the primary “winners” in the BH process.
The researchers used a nationwide, citizen-science program and two local standardized surveys to analyze trends of common native and non-native birds during the last 15 years across Israel, where large populations of very destructive invasive alien bird species were introduced towards the end of the 20th century.
Previous studies conducted in Israel have shed light on the mechanisms through which invasive bird species can impact native species, notably competition. This highlights the importance of acting now, especially since non-native species are currently spreading from human-dominated areas to more natural environments.
The Technion scientists urged the adoption of appropriate management strategies to halt or mitigate the spread of non-native birds. Otherwise, the researchers predict that the bird communities will become increasingly homogenized and dominated by non-native species.