Radioactive Robins and other birds

Why do House Sparrows Passer Domesticus chew Hop and Ligustrum leaves?

House Sparrows Passer domesticus like to  chew leaves of Ligustrum or  Privet – Wikipedia
         but when given a choice they adults and even fledgelings (both females & males) prefer to to             
        chew fresh Hop leaves  Humulus lupulus – Wikipedia
 
        Male House Sparrows however tear thin strips of bark from one year old Hop                       
        branches in spring and seem to chew on them as well.
  
       There is no explanation for the sparrows’ behaviour yet nor is the effect of the chemicals             
       entering the sparrows’ bodies known yet.
a House Sparrow Passer domesticus ad male with HOP skin 09052024 7169 Oostvoorne,The Netherlands c Norman Deans van Swelm
a House Sparrow Passer domesticus ad male with HOP skin 09052024 7176 Oostvoorne,The Netherlands c Norman Deans van Swelm
a House Sparrow Passer domesticus ad male with HOP skin collecting more 09052024 7180 Oostvoorne,The Netherlands c Norman Deans van Swelm.jpg
a House Sparrow Passer domesticus ad male with HOP skin collecting more 09052024 7182 Oostvoorne,The Netherlands c Norman Deans van Swelm.jpg
a House Sparrow Passer domesticus ad male with HOP skin using tongue 09052024 7164 Oostvoorne,The Netherlands c Norman Deans van Swelm.jpg
a House Sparrow Passer domesticus female chewing leaf from Hop 31082023 4454 Oostvoorne,The Netherlands c Norman Deans van Swelm.jpg
a House Sparrow Passer domesticus juv chewing Hop leaf 31082023 4938 Oostvoorne,The Netherlands c Norman Deans van Swelm.jpg
House Sparrow Passer domesticus male chewing leaf 07032010 8523 Berkel & Rodenrijs,The Netherlands c Norman Deans van Swelm.jpg
House Sparrow Passer domesticus male chewing Ligustrum leaf 07032010 8513 Berkel & Rodenrijs,The Netherlands c Norman Deans van Swelm.jpg
House Sparrow Passer domesticus male chewing Ligustrum leaf 07032010 8538 Berkel & Rodenrijs,The Netherlands c Norman Deans van Swelm.jpg