al ▁to ▁the ▁har riers ▁themselves , ▁as ▁well ▁as ▁ra ref ying ▁their ▁pre y , ▁in ▁particular ▁large ▁insect s . ▁The ▁modification ▁of ▁agricult ural ▁pract ises , ▁with ▁an ▁evolution ▁towards ▁more ▁int ensive ▁far ming ▁also ▁puts ▁pressure ▁on ▁har riers , ▁with ▁faster ▁growing ▁cro ps ▁prevent ing ▁those ▁birds ▁that ▁nest ▁in ▁far ml ands ▁from ▁finishing ▁their ▁n id ification ▁before ▁their ▁cl ut ches ▁are ▁destroyed ▁by ▁har vest ing ▁machines . ▁Despite ▁a ▁generally ▁negative ▁tr end ▁there ▁are ▁local ▁cases ▁when ▁the ▁population ▁has ▁increased , ▁such ▁as ▁in ▁Sweden ▁or ▁in ▁Germany ▁in ▁the ▁ 1 9 9 0 s . ▁These ▁local ▁tr ends ▁show ▁that ▁while ▁they ▁have ▁access ▁to ▁suitable ▁habit ats ▁and ▁food ▁supply ▁there ▁can ▁still ▁be ▁positive ▁develop ments . ▁ ▁Social ▁behaviour ▁and ▁bre eding ▁It ▁can ▁be ▁both ▁solit ary ▁and ▁gre g ari ous ▁at ▁times , ▁both ▁during ▁the ▁bre eding ▁season ▁and ▁in ▁winter ▁qu arters . ▁A ▁bre eding ▁pair ▁may ▁associate ▁with ▁others ▁to ▁form ▁loose ▁colon ies , ▁with ▁as ▁many ▁as ▁ 3 0 ▁n ests ▁in ▁the ▁same ▁area , ▁sometimes ▁as ▁close ▁as ▁ ▁apart . ▁Sem i - colon ial ▁nest ing ▁is ▁not ▁due ▁to ▁a ▁short age ▁of ▁nest ing ▁sites , ▁but ▁ar ises ▁rather ▁from ▁the ▁need ▁to ▁provide ▁a ▁better ▁defence ▁against ▁pred ators . ▁The ▁actual ▁area ▁def ended ▁by ▁both ▁partners ▁covers ▁only ▁ ▁around ▁the