Bird Watching (UK) - - Species Jack­daw -

LIt’s quite a dif­fi­cult con­cept, and there is no real an­swer. Ev­ery species has its crosses to bear, and ev­ery pair ev­ery­where has had chal­lenges to face. Many in­di­vid­u­als, of all kinds and for all man­ner of rea­sons, have failed com­pletely. They might have failed even to ac­quire a ter­ri­tory, or died hero­ically try­ing to save their off­spring. A com­bi­na­tion of con­di­tions might have ren­dered breed­ing harder than usual. But what I’m ask­ing is ac­tu­ally a deeper ques­tion. Are there some birds for which breed­ing is, rou­tinely, un­usu­ally dif­fi­cult? And is there any sci­en­tific ev­i­dence that might show such a thing? Well, it might stretch a few ar­gu­ments a lit­tle, but I would ar­gue that there is. Step for­ward, the Jack­daw. You’re prob­a­bly sur­prised. The Jack­daw is a jaunty crea­ture, with a care­free mien if not a care­free na­ture. Our hu­man im­pres­sions, ir­rel­e­vant though they are, would place the Jack­daw in the happy camp. We some­times see them near their roost-sites in an evening play­ing – yes, surely play­ing – in the skies, cir­cling, tum­bling, calling in ex­cite­ment. Jack­daws go­ing to bed are like chil­dren on a sleep­over, full of ex­u­ber­ance. Th­ese corvids nest in colonies, too, where they are equally good value to watch, mess­ing about by tree holes or chim­ney pots. So are the Jack­daws suf­fer­ing up in the rooftops? It does not seem right. But the Jack­daw’s breed­ing lot is a tough one to bear, and there are two sound bi­o­log­i­cal rea­sons to as­sume that this is so.

The as­sump­tions stem from the fact that Jack­daws find it hard to ac­quire enough food to feed their young­sters. In con­trast to the more om­niv­o­rous na­ture of the larger corvids, Jack­daws feed their off­spring on the sum­mer in­sect bloom. They bring in such items as grasshop­pers, flies, ants, bee­tles and cater­pil­lars, which they pre­dom­i­nantly find on the ground, in long grass. The in­sect bloom is short, and some­times catches Jack­daws out, if their breed­ing is de­layed. So what bi­o­log­i­cal quirks tell us that the Jack­daw has a hard time bring­ing in food? Well, I hope you are ready for this, be­cause it is quite up­set­ting stuff. Jack­daws prac­tise a method of chick-rear­ing called brood re­duc­tion, which is ev­ery bit as chilling as it sounds. Brood re­duc­tion is an over­pro­duc­tion strat­egy de­signed to cater for good years and bad when a food sup­ply is un­pre­dictable. It is ac­tu­ally quite a sim­ple al­ter­ation of nor­mal prac­tice, but the con­se­quences are pro­found. What Jack­daws do is to space out their egg-lay­ing and to be­gin in­cu­ba­tion be­fore the clutch is com­plete. Some­times they lay each egg in their clutch of three to six a cou­ple of days apart, or even three, and then the fe­male be­gins sit­ting af­ter her sec­ond egg comes along. This is quite dif­fer­ent from what most birds in your gar­den and be­yond do. Tits, for ex­am­ple, lay First-born Jack­daws get a head start over their sib­lings An adult pauses be­fore re­sum­ing the grind of feed­ing the brood


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