A new study has shown that Crag Martins wintering in Gibraltar show remarkable faithfulness to the caves in which they roost.

A new study at the Gorham’s Cave Complex UNESCO World Heritage Site has shown that Crag Martins wintering in Gibraltar show remarkable faithfulness to the caves in which they roost.  It is the first time that such a high degree of faithfulness within a roost has been demonstrated in birds over successive years.

The study is the result of a collaboration between two Associate Campuses of the University of Gibraltar’s Institute of Life and Earth Sciences - the Gibraltar Botanic Gardens and the Gibraltar National Museum - and the Gibraltar Ornithological & Natural History Society. 

"Crag Martin neontology complements taphonomy at the Gorham’s Cave Complex" has been published in the journal Scientific Reports, which is a Nature research journal.  It represents the latest chapter in the Gorham’s Cave Story.

Crag Martins have used the caves at the Gorham’s Complex consistently since the Pleistocene, when they shared these caverns with Neanderthals.  They gather in their thousands at the caves during winter nights, when they use these for shelter.  Gibraltar holds the largest known roost in the world, with a record 12,000 birds this past winter, representing 1-2% of the European population.

The study shows that not only do the same birds return to the same caves within and between years, but that the birds in the different caves differ in body condition, indicating that some caves provide better roosting sites than others.  These differences in quality of caves could have translated to other species that have used the caves in the past.

The findings shed light on the winter ecology of a bird with a very long association with Gibraltar.  It indicates that such fidelity and assortment may thus have evolved over thousands of years, and it allows us to hypothesise on the relative value of the caves to fauna more generally. 

Finally, they illustrate the outstanding value of the Gorham’s Cave Complex as a site for original research of faunas past and present.

The article can be accessed at: www.nature.com/articles/s41598-021-95974-9