The latest Sandgrouse issue contains an article about the occurrence of Caspian and Black-headed Penduline Tits in Azerbaijan by Michael Heiß and Christoph Himmel: https://osme.org/sandgrouse/sandgrouse-44-1/
Titel: Recent status of Caspian Penduline Tit Remiz pendulinus caspius and Black-headed Penduline Tit Remiz (pendulinus) macronyx in Azerbaijan.
Summary: Caspian Penduline Tit and Black-headed Penduline Tit are known from the literature to occur in Azerbaijan. Neither has been reported for decades, but a sudden increase in sightings of Caspian Penduline Tits in 2019 might suggest an irruptive migratory influx to Azerbaijan. The status of Black-headed Penduline Tit remains unclear.
The idea and some basic results came from this very enjoyable trip that included several sightings of the magnificent and little-known Caspian Penduline Tit:
Birding Azerbaijan 