How does behaviour and eyesight affect bird-window collisions?

The artificial environment has now become so integral to the planet's surface it would be hard to imagine a time without it. Towering skyscrapers and apartment blocks dominate the skies of our major cities; houses of all shapes and sizes sprawl across our vast suburbs; a solid, unmoving presence among the fluidity of nature. Our need to create and develop has propelled us through the centuries however, it has inadvertently restricted others.

These changes to the world around us are all but irreversible; demanding that nature constantly adapt to our needs. As we have constructed our homes, we have replaced the homes of others. As we have chosen our homelands, we have displaced others. As we have built towards the skies, we have intercepted the pathways of others. Our artificial structures are the root cause of bird-window collisions however, elements of nature perpetuate the risk.

Bird migration

It is predicted that 70% of migratory birds pass through towns or cities in Northern America and that an increase in collisions coincides with the migratory and breeding seasons. During the autumn months, when fledglings are present, it is predicted that mortality is 3.7 times more likely than collisions during the spring migration. Not only do birds have multiple habitat and buildings to navigate during their long journeys, migratory birds must brave the bright city lights. Illuminated buildings and infrastructure can cause disorientation and a trance like behaviour, often resulting in fatal collisions. Nighttime migrators are 10.9 times more likely to collide with illuminated buildings, than daytime migrators.

Bird behaviour

Species that are naturally faster fliers are also more vulnerable to fatal window collisions, due to their higher flight velocities. This increases the severity of injuries and the likelihood of a fatality. North American studies have highlighted that some of the most vulnerable species are passerines (the perching birds), falcons, sparrows, robins and doves. Robins are thought to be particularly vulnerable due to their flight speeds. The beginning of the breeding season, when sexual aggressiveness, distracted behaviour and territorial defence is at its highest, also increases the risk of bird-window collisions. 

Bird eyesight

Understanding a bird's vision will help to understand what a bird sees when approaching windows. It is known that birds can see in UV light however, this varies across species. Most species see in VS light whereas, species such as passerines (the largest order of birds), parrots and gulls, can see in UVS light. Additionally, various behavioural and physiological factors can influence the way a bird views the world, such as; the way a bird feeds; its position in the food chain and its surrounding environment. Previous research has suggested that the placement of the eyes and the resolution and direction of vision, influence the limitations of a bird's ability to detect hazards, such as predators and solid structures.  

Assess your home or business

When mitigating bird-window collisions, it is important to acknowledge how a bird interacts with the world around it. Even though our knowledge is always evolving and there will always be questions that we are yet to find the answers to; it is our responsibility use the information we do know to better protect the environment around us.

If you would like to know how you can take steps to assess your home or business to reduce bird-window strike, then check out our blog post here.

Don’t forget to report any bird window/car strikes using our online survey. Your input is greatly appreciated and essential in helping us further our understanding of bird-window and bird-car strikes.

This project received financial support from the Australian Bird Environment Foundation of BirdLife Australia, The Belaberi Foundation and The Australian Geographic Society

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