More often that not, where bird exclusion is important to the client, we find that the finishing work from ‘other trades’, in regard to proper birdproofing, is neither that trade's priority, nor its area of expertise.
A typical example is the entry by small birds through the rear storage areas of large retail operations into their trading areas. Penetrations made through a common roof area or dividing walls are often left open. Cable trays and wiring conduits are a frequent entry point which should be noted and fixed during the building supervision, not in the weeks following practical completion.
The following example is outside a food factory. With this poor standard of ‘proofing’ there’s little wonder that the birds will move quickly to get closer to the action. The availability of food, even if only from the garbage compactor or, more worryingly from the production areas, coupled with safe nesting areas makes it a choice location for birds to colonise in the building structure.

Poor Finishing Work
This leads to gaps where birds can gain entry to facilities and cause hygiene issues
The better option: Think about birdproofing from the start of your project. Deal with a reputable expert in the field of birdproofing who can provide you with effective strategies to prevent costly bird infestation problems later.