In poultry slaughterhouses, birds arrive in batches. Birds are delivered in holders (2), are unloaded and are connected to carriers (14). The birds are then introduced into the slaughterhouse and slaughtered, after which further processing take place. The supply is variable over the course of time. However, the slaughtering is a continuous process. The present invention evens out the supply variability, so that a uniform stream of birds which is well matched to the continuous process in the slaughterhouse is obtained. A conveyor device (8, 9) having a controllable speed is positioned between the point at which the birds are unloaded from the holders and the point at which the birds are connected to a carrier. The speed of this conveyor device is controlled in such a manner that the number of birds which leaves the conveyor device is substantially uniform. It is also possible to control the speed of unloading. It is also possible for measurements to be performed at various points in the system and for these measurements to be fed back to the controllable conveyor device. In this way it is then possible to automatically generate a uniform stream of birds.