Why Do Gull-Billed Terns Gelochelidon nilotica Feed on Fiddler Crabs Uca tangeri in Guinea-Bissau?

[摘要] Gull-billedTernsGelochelidonniloticawinteringinGuineaBissaumainlyfedonfiddlercrabsUcatangeriandwereoccasionallyseenfeedingonfishandlocusts.Asfiddlercrabshavealowenergycontent,ternsneedalargegrossintaketomeetdailyenergydemands.Fiddlercrabsalsohavealowratioofdigestiblefleshtoexoskeleton,andthereforeternfoodintakemaybelimitedbygutcapacity.ActivitybudgetsofGullbilledTernsfeedingonfiddlercrabsshowedthataconsiderablepartofthetimewasspentresting.Thedurationofrestingintervalsincreasedwithenergyintakeandwaspositivelycorrelatedwiththemetabolisableenergycontentofthecrabeaten,suggestingthatrestingperiodswererequiredforaproperdigestion.Thepoorqualityoffiddlercrabswasoffsetbyhighcapturerates.Sodailyenergyexpenditureoftheternscouldeasilybemetbyfeedingonfiddlercrabs.Evenwhenrestingpauseswereincludedinforagingtime,foragingforonly1.5hoursonfiddlercrabssatisfiedtheterns'dailyenergydemands.Instead,feedingonenergy-richfishwouldrequireabout2.5hourstosatisfydailyenergydemands.ComparedtothemorespecialisedpiscivorousLittleTernSternulaalbifronsandSandwichTernSternasandvicensis,capturerateoffishwaspoorinGull-billedTerns.Fromanenergeticpointofview,winteringGull-billedTernsfeedingonfiddlercrabsseemtohaveaneasylivinginGuineaBissau.

[学科分类] 动物科学

[关键词] Africa