Global population estimates of Pacific Golden Plovers (Pluvialis fulva range from as low as 100,000 to as high as 1,000,000. Earlier reports suggest that between 4,000 and 50,000 Pacific Golden Plovers migrate through the Mongol-Daguur Strictly Protected Area in North-Eastern of Mongolia, which is an important area for numerous breeding and migrating birds. Given these estimates, the Mongol-Daguur Strictly Protected Area may host a significant portion of the world's population during migration.
To gain a better understanding of the stopover behaviour of Pacific Golden Plovers, and of the importance of this area for this wader species, a Dutch-Mongolian expedition was set up. During a 16 day period, Pacific Golden Plovers on migration were counted, caught and measured.
Between 15 May and 30 May 2005, 323 Pacific Golden Plovers were caught. Among the 294 birds released were 174 males (of which 12, 6.9% were 2nd year birds) and 116 females (of which 8, 6.9% were 2nd year birds). During the catching period, the proportion of males decreased from 60% to 30%. Counts of migrating birds during our stay in the area showed three peaks of around 2.000 or more individuals. This pattern was likely related to patterns of high winds. We observed an estimated 11.3-12.5% (12,500 birds) of the world population of Pacific Golden Plover (100,000-1,000,000 birds), making this site an Important Bird Area category A4i (hosting >1& of the global population) for this species.
The body mass of the Pacific Golden Plovers caught ranged form 100 to 139 g on the first catching day to between 152 g an 182 g on the last catching day. Over the whole catching period this corresponded to an average daily mass increase of 2.8 g. Males and females showed very similar patterns in mass change. A similar mass increase (3.1 g/day) was found in the dissected birds. Measurements showed that this mass increase was the result of both storage of fat and an increase of total fat-free dry-mass, with individuals reaching fat stores of up to 40 g.
A radio receiver was used to try and track Pacific Golden Plovers that were supplied with a radio transmitter by O.W.Johnson on the Mariana Islands. However, no individuals were recorded in our study area. However, even if individuals from the Mariana Islands would migrate through the Mongol-Daguur area, the probability of tracking them would be low due to the vastness of the area and the limited range of the receiver.
Although the wind conditions made catching difficult, we were very successful in getting good data on numbers, sex-ratio, mass change and body condition (muscle and fat compostition) of this migratory species during stop-over in the Mongol-Daguur area. The mass increase indicates that this area is an important stopover site for the Pacific Golden Plovers on spring migration, with males presumably migrating earlier than females in order to acquire territories on the breeding grounds.
Based on the results of our study, we can conclude that the Mongol-Daguur Strictly Protected Area is an important stopover site for migrating Pacific Golden Plovers using the area to refuel during spring migration. We suggest further studies be carried out to get more detailed information on numbers, individual length of stay and other population characteristics. We encourage further collaboration with the National University of Mongolia, because local knowledge proved indispensible to the success of this project and will be invaluable to any future long term monitoring project.