Francisco Marquez / Penduline tit (Remiz pendulinus) building a nest, Prespa National Park, Prespes, Greece, May.

Jan Wegener / Eurasian Penduline-Tit (Remiz pendulinus), Brandenburg, Germany

Bruno D'Amicis / Penduline tit (Remiz pendulinus) female peering out of the nest. Germany

Dietmar Nill / Male + female Penduline tits {Remiz pendulinus} at nest, Bulgaria.

Thomas Hinsche/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male building nest, Saxony-Anhalt, Germany

Juan Carlos Munoz / Eurasian penduline tit (Remiz pendulinus) nest hanging from branch. Shumen, Bulgaria, April.

Juan Carlos Munoz / Eurasian penduline tit (Remiz pendulinus) at partially built nest. Shumen, Bulgaria, April.

Juan Carlos Munoz / Eurasian penduline tits (Remiz pendulinus) building nest. Shumen, Bulgaria, April.

Juan Carlos Munoz / Eurasian penduline tit (Remiz pendulinus) building nest. Shumen, Bulgaria, April.

Juan Carlos Munoz / Eurasian penduline tit (Remiz pendulinus) building nest. Shumen, Bulgaria, April.

Juan Carlos Munoz / Eurasian penduline tit (Remiz pendulinus) building nest. Shumen, Bulgaria, April.

Ingo Arndt / Eurasian penduline-tit (Remiz pendulinus) nest, Germany, June.

Francisco Marquez / Penduline tit (Remiz pendulinus) removing material from an old nest to make a new one, Toledo, Spain, May.

Francisco Marquez / Penduline tit (Remiz pendulinus) building a nest, Toledo, Spain, May.

Francisco Marquez / Penduline tit (Remiz pendulinus) building a nest, Toledo, Spain, May.

Francisco Marquez / Penduline tit (Remiz pendulinus) building a nest, Toledo, Spain, May.

Jussi Murtosaari / European penduline tit (Remiz pendulinus), male perched on willow, Jyvaskyla, Finland, April.

Jussi Murtosaari / European penduline tit (Remiz pendulinus), males, Jvaskyla, Finland, April.

Sven Zacek / Penduline tit (Remiz pendulinus) overwintering in Estonia and searching for food in reeds in Tartumaa, Estonia. January.

Sven Zacek / Penduline tit (Remiz pendulinus) male on nest, Tartumaa, Estonia. May 2013.

Sven Zacek / Male Penduline tit (Remiz pendulinus) building nest at sunrise, Tartumaa, Estonia, April.

Juan Carlos Munoz / Men holding Eurasian penduline tit (Remiz pendulinus) at bird ringing demonstration, Hula Valley, Israel, November 2014.

Filippo Nucifora / Eurasian Penduline-Tit (Remiz pendulinus) male, Switzerland

Jan Wegener / Eurasian Penduline-Tit (Remiz pendulinus), Brandenburg, Germany

Jan Wegener / Eurasian Penduline-Tit (Remiz pendulinus) male at nest, Brandenburg, Germany

Winfried Wisniewski / Eurasian Penduline-Tit (Remiz pendulinus) male on reed blade, Biebrza National Park, Poland

Winfried Wisniewski / Eurasian Penduline-Tit (Remiz pendulinus) male looking out of nest, Biebrza National Park, Poland

Winfried Wisniewski / Eurasian Penduline-Tit (Remiz pendulinus) male building its nest, Biebrza National Park, Poland

Dietmar Nill / Penduline tit (Remiz pendulinus) male in nest, Germany

Konstantin Mikhailov / Penduline tit {Remiz pendulinus} pair building nest, Central Russia, April

Konstantin Mikhailov / Penduline tit {Remiz pendulinus} building nest, Central Russia, April

Kerstin Hinze / Penduline tit (Remiz pendulinus) flying to its nest, Bulgaria

Dietmar Nill / Penduline Tit (Remiz pendulinus) perched on a twig, calling. Bulgaria

Bruno D'Amicis / Penduline tit (Remiz pendulinus) male peering out of nest, Germany

Bruno D'Amicis / Penduline tit (Remiz pendulinus) male peering out of the nest, Germany

Duncan Usher / Eurasian Penduline-Tit (Remiz pendulinus) hanging on nest, Europe

Hermann Brehm / Penduline tit at nest, Germany

Thomas Hinsche/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male building nest, Saxony-Anhalt, Germany

Thomas Hinsche/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male in nest, Saxony-Anhalt, Germany

Mario Suarez Porras/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male at nest, Spain

Robin Chittenden / Penduline tit (Remiz pendulinus) on reeds, Dingle Marshes, Suffolk, England, November

Robin Chittenden / Penduline tit (Remiz pendulinus) on reed, Dingle Marshes, Suffolk, England, November

Thomas Hinsche, BIA / Eurasian Penduline-Tit (Remiz pendulinus) pair calling at nest, Saxony-Anhalt, Germany

Jose Luis Gomez de Francisco / Penduline tit at nest {Remiz pendulinus} Spain

Jose Luis Gomez de Francisco / Penduline tit flying to nest, Spain.

Johannes Melchers/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male at nest, Armenia

Mateusz Piesiak / European penduline tit (Remiz pendulinus) building its nest in slow motion, Lower Silesia, Poland, May.

Mateusz Piesiak / European penduline tit (Remiz pendulinus) building its nest in slow motion, Lower Silesia, Poland, May.

Mateusz Piesiak / European penduline tit (Remiz pendulinus) building its nest in slow motion, Lower Silesia, Poland, May.

Mateusz Piesiak / European penduline tit (Remiz pendulinus) building its nest in slow motion, Lower Silesia, Poland, May.

Pal Hermansen / Penduline tit (Remiz pendulinus) perched on Reed beside spider's web with many trapped insects. Danube delta, Romania. May.

Pal Hermansen / Penduline tit (Remiz pendulinus) perched on Reed. Danube delta, Romania. May.

Thomas Hinsche/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male building nest, Saxony-Anhalt, Germany