As dusk falls over the fields on a late winter evening, a somewhat unusual counting session begins for the birdwatcher. Instead of scanning for birds with binoculars, the task is primarily to stand still, listen, and wait for a brief “kirrreck” call. This is precisely when the population of the Grey Partridge (Perdix perdix) can be surveyed with particular reliability.
A standardized line-transect survey method using a playback call has become established in Germany for monitoring grey partridge populations. It is employed in initiatives such as the Monitoring of Rare Breeding Birds (MsB) and the project “Save the Grey Partridge – Promote Biodiversity!” (“Rebhuhn retten – Vielfalt fördern!”). The crucial factor is not simply to locate as many partridges as possible, but to conduct the survey under comparable conditions. Only in this way can results be meaningfully compared across different years and regions.
The survey is carried out on dry evenings with little to no wind, following a designated route—approximately 1 to 1.5 kilometers long—through suitable agricultural landscapes. The route preferably follows farm tracks and encompasses a diverse range of grey partridge habitats, such as wildflower fallows, strips of tall, undisturbed grass, and low hedges.
The optimal time for the survey is late winter or early spring—specifically, the turn of the month between February and March. Current MsB standards specify a survey period between February 11 and March 20. The ideal time is roughly 30 to 60 minutes after sunset, when the cocks are particularly vocal during their courtship displays. This calling activity typically declines as March progresses.
A playback device is used at fixed points spaced approximately 150 to 200 meters apart. The call of a male grey partridge is played via an external speaker; cocks in the vicinity often respond with their own calls, thereby revealing their location. As soon as a male responds, the acoustic lure is switched off. This prevents unnecessary disturbance and reduces the risk of a male moving towards the sound source.
A key factor to consider is the risk of double-counting. An unpaired male may respond to the lure and subsequently move towards the surveyor; therefore, the direction of the call, the distance, and any movements must be carefully monitored. Males calling spontaneously should also be briefly checked using the lure to ensure other individuals are not overlooked.
Visual observations complement acoustic surveys. They can detect hens, family groups, and other individuals that are not calling. However, the standardized recording of calling males remains central to quantitative population estimation. Modern methods, such as thermal imaging cameras, can detect additional individuals but do not currently replace the established monitoring standard.
Finally, repeated surveys are crucial for assessing population trends reliably. While individual observations are valuable, only standardized counts along comparable routes over several years reveal changes in the population. Anyone documenting their observations on ornitho.de should therefore carefully record the location, date, number of individuals, behavior, and—if possible—a breeding status code.
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