PiCAS INTERNATIONAL

This week, Sky News reported that one of the theories put forward for the collapse of a 40-year old bridge in Minnesota, USA, was accelerated corrosion due to pigeon guano!  This has to be one of the most ludicrous theories ever put forward for a disaster of this type and on this scale, particularly when 13 people lost their lives and over 100 people were injured. 

River/road bridges and rail/road bridges are one of the most common and well used roosting/breeding sites for feral pigeons worldwide and it is not uncommon to find literally thousands of pigeons roosting and breeding under larger bridges.  The issue of pigeon occupancy under bridges is not lost on Bridge Inspectors whose job it is to undertake annual inspections of bridges to confirm that they are safe.  So why, if engineers are now saying that corrosion of steelwork was accelerated due to the acid present in pigeon guano, was this issue not raised and dealt with prior to the bridge becoming so badly corroded that it collapsed?

It is possible that those responsible for the upkeep of the bridge were controlling pigeons by the use of a narcotic bait (poison) called alphachloralose, the most commonly used method of pigeon control in the USA but a method of control that is rarely used in the UK due to the fact that its use causes extreme suffering in the target species  (animal welfare laws are extremely relaxed in the US relative to similar legislation in the UK).  Scientific research, together with research undertaken by PiCAS International, has proven, conclusively, that pigeon populations cannot be controlled and reduced in size by use of lethal methods.  In fact, when lethal methods are used to control pigeon populations, pigeon flock size will rise, not fall, with every killing operation.  If lethal controls had historically been used to control pigeons resident under this bridge, with no other methods of control provided, this may be one of the contributory factors in relation to the collapse of the bridge. 

Constant use of culling will always act to increase pigeon flock size and when those responsible for the safety of a structure of this nature are led to believe that lethal control is the most appropriate and most effective option, it is just possible that the structure was compromised due to the sheer volume of pigeon guano on/within the bridge.  When protecting a bridge of this size and scale, controls are required that will physically prevent pigeons accessing areas below the road deck for the purpose of roosting and breeding.  The most appropriate option to protect the underside of a road or rail deck is to net the entire structure with an industrial gauge of nylon bird netting called ‘anti-litter netting’ - this is the only type of nylon bird netting that PiCAS will recommend.  This type of heavy-duty netting, although expensive, will stand the test of time where the protection of a structure of this nature is concerned.  Problems arise, however, when the bridge must be accessed for routine maintenance and this is often why a decision is taken to avoid the use of physical deterrents or bird exclusion devices.  The cost of removing and then reinstating nylon bird netting from a structure of this size would be extremely high.   

A good example of just how entrenched pigeon-related problems can become under large river/road or road/rail bridges is the case of the Tyne Bridge in Newcastle-on-Tyne, UK.  When PiCAS was called in by Newcastle City Council to advise on the control of pigeons on this massive structure the Council confirmed that during the last operation to clean the bridge and remove a 12-year build up of pigeon guano, over 12 tonnes of guano was removed!  

To blame the feral pigeon for the collapse of a bridge is absurd and the question must inevitably be asked - why was the steelwork allowed to corrode away due, in part, to the acid from pigeon guano?  Surely this issue should have been raised during annual inspections and steps taken to remove the build up?  Is this just another case of the pigeon being blamed for human errors?