That's an excellent question that many city planners and environmentally-conscious residents are asking these days. The relationship between trash can design and urban wildlife management is more complex than it initially appears.
Based on research from urban ecology studies, trash cans need to be sufficiently deep to prevent birds from accessing contents while perched on the rim. The general consensus among wildlife experts suggests that containers should have a depth-to-width ratio where the depth is at least 2-3 times greater than the opening diameter. This creates what's known as a "visual deterrent" – birds can't easily see or reach the bottom, making them less likely to attempt foraging.
However, depth alone isn't the complete solution. The design of the opening matters tremendously. Narrow openings (typically less than 6 inches across) combined with sufficient depth (around 24-30 inches) create an effective barrier. Many birds, particularly crows and gulls, are intelligent enough to avoid containers where they cannot clearly assess potential risks or easily escape.
What's particularly interesting is how different bird species interact with various designs. Pigeons, for instance, require different deterrent measurements than larger gulls. This is why many modern urban solutions incorporate not just depth, but also weighted lids, baffle systems, and sometimes even slightly opaque materials that limit visibility.
The most successful municipal programs combine adequate depth with other features like secure lids and regular maintenance schedules. After all, the deepest trash can won't deter birds if it's overflowing with accessible waste. The key is creating an integrated system where depth works in concert with other design elements to make scavenging unrewarding for our feathered city dwellers.