Avian paramyxoviruses (APMVs) are classified into nine different serotypes (APMV 1-9). Virulent strains of APMV-1 are already well characterized as the etiologic agent of Newcastle disease (ND), an important disease in poultry that is potentially capable of infecting all orders of avian species. However, very little is known about the other eight serotypes, the majority of which can cause disease in domestic birds. The role of synanthropic and semi-free-range birds as reservoirs of avian paramyxoviruses is not well understood and the main objective of this work was to evaluate the seroprevalence of APMV 1-9 in these kind of birds. A total of 296 sera, oropharyngeal swabs, and cloacal enemas were collected from semi-free-range birds belonging to four different species: feral pigeons (Columba livia var. domestica), hybrid ducks (Anas sp.), domestic geese (Anser anser domesticus), and white storks (Ciconia ciconia). Antibodies against NDV were found in 56.3% of domestic geese, 42.9% of feral pigeons, and 30.4% of hybrid ducks. Antibodies for other APMVs (-3, -4, -6, -7, -8, -9) were also found. Seven positive individuals were positive to real-time RT-PCR detection, all of them feral pigeons captured in 2006 and 2007. The results obtained reinforce the idea that semi-free-range birds may be good sentinels for the detection of NDV and other avian paramyxoviruses.