How do land use and agricultural practices affect the abundance and population dynamics of the red partridge?

    In the last decade the population of red partridge in Castilla-La Mancha has decreased by 51%, this decline being greater in those areas where more grassland has been lost and where the area of ​​tree crops has increased.


    La red-legged partridge (Alectoris rufa) It is a common species of southwestern Europe, whose natural populations inhabit mainly the Iberian Peninsula, where it is of great socioeconomic and ecological importance, being one of the main small game species in Spain and an important trophic resource for many Iberian predators. It is a generalist species, which inhabits both natural environments and agricultural mosaics, although today the most favorable areas for the red partridge are dominated by farmland.

    As is the case with many other species, Red partridge populations in Spain decreased sharply in the second half of the XNUMXth century, as interpreted from the evolution of hunting bags. This decline could be due to the abandonment of the forest and changes that occurred in the cultivated lands associated with agricultural intensification, such as the loss of habitat heterogeneity, the advancement of the cereal harvest and the use of agrochemical products. This decline could have continued in recent decades, although the magnitude of the recent population decline is less quantified (and sometimes even questioned from hunting sectors).

     

    The red partridge is of great socioeconomic and ecological importance in the Iberian Peninsula (Photo: François Mougeot).

    Now scientists from Research Group in Game Resources and Wildlife Management of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), in collaboration with scientists from the Department of Zoology and Animal Cellular Biology of the University of the Basque Country (UPV/EHU) and the Department of Animal Biology of the University of Malaga, have studied on a large scale (in the entire territory of Castilla La- Mancha) the relationship between the population density of red partridge (accurately measured by statistical models that take detectability into account) and the composition and management of agricultural land. They have also estimated the population trend of the species in the region during the last decade and its relationship with the changes that occur in the composition of the agricultural landscape. This study has been based on the data collected by the rangers of the Junta de Comunidades de Castilla La-Mancha between 2010 and 2017 as part of the Hunting and Fishing Service program for monitoring the red partridge.

    The results obtained in this work show that the abundance of red partridge is closely related to the composition and management of farmland. The abundance of this species is positively related to the extent of natural vegetation. (particularly pastures) and traditional dryland vineyards, but negatively related to the extension of irrigated vineyards and tree crops. On the other hand, some limiting climatic factors for red partridge populations are also described, such as low winter temperatures and high autumn rainfall.

     

    The abundance of the red partridge is positively related to the extent of natural vegetation and traditional dry-land vineyards (Photo: Xabier Cabodevilla).

    The study also shows that the abundance of red partridge is conditioned by the management of some crops, as is the case of the vineyard. The Red Partridge is highly dependent on water during the summer and might be attracted to irrigated vineyards for drinking. In fact, another study has shown that the red partridge seems to use trellised vineyards more frequently than traditional ones during the summer. However, the application of fertilizers through irrigation water is a common practice in vineyards (which are drip irrigated), making irrigation water toxic to birds.

    In this regard, the study shows that a higher proportion of irrigated vineyards in the landscape is associated with a lower abundance of red partridge, but this negative relationship is minimized in areas sensitive to nitrate contamination, where there are limitations regarding the amount of fertilizer that can be applied to irrigation water. This suggests that fertigated crops could be an important ecological trap for this and other agricultural bird species.

    The study also shows that the population of red partridge has suffered a population decline of 51% between 2010 and 2017 in Castilla La-Mancha, which is one of the most important regions for the species. It should be noted that this decline was not linear throughout the study period, but occurred mainly in two years (2013 and 2014), with periods of relative stability before and after. This suggests that this decline may be due to one-off stochastic events (involving extremely poor survival or reproduction in certain years), but that environmental or demographic conditions prevent the population from recovering later.

    On the other hand, in line with the results on abundance, Red partridge population trends are modulated by changes in land use: the decline was more marked in areas where the proportion of pastures (natural vegetation) has decreased the most, and where tree crops have increased the most.

     

    The red partridge population has suffered a population decline of 51% between 2010 and 2017 in Castilla La-Mancha (Photo: Rubén Ibáñez).

    This result highlights the delicate situation of this emblematic bird, of great socioeconomic and ecological importance. Scientists, public institutions, farmers and hunting federations should work together to solve the conservation problem facing the red partridge.. Possibly the conservation of this species, as well as that of other agricultural birds in sharp decline such as the little bustle or the sandgrouse, requires rethinking the agricultural policy, avoiding intensification and the excessive use of agrochemical products, restricting the expansion of tree crops and promoting patches of natural or semi-natural vegetation, while ensuring that hunting is carried out sustainably.

    In addition, the results of this study emphasize the need for continuous monitoring of the species and also provide relevant information to improve its monitoring. The results indicate that the best time to carry out red partridge counts (within the time frame of our study, between April and July) is at the end of April/beginning of May or in July. Regarding the sampling time, counting at dawn seems to be the most efficient in early spring, while in July it seems more appropriate to count at sunset. This should be taken into account when designing monitoring programmes. Either way, the study indicates that it is advisable to use repeat counts to account for detectability during the modeling process, in order to obtain more accurate abundance estimates.

    En general, the results obtained in this work show the value of mosaic agricultural landscapes for agricultural birds, such as the red partridge. An agricultural landscape that combines the traditional dryland cereal system, with plots of natural herbaceous vegetation (such as pastures and borders) and crops with abundant vegetation cover (such as traditional dryland vineyards), thus offering places for foraging and refuge to avoid to predators and high summer temperatures.

    The scientific publication of this research is available at: