function update(dt){
 const vision=val("vision");
 const speed=val("speed");
 const maxForce=.11;
 const old=birds.map(b=>({...b}));

 birds.forEach((b,i)=>{
  if(!visible[b.type])return;

  let sx=0,sy=0;
  let ax=0,ay=0;
  let cx=0,cy=0;
  let same=0;

  const own=species[b.type];
  const range=vision*own.vision;

  for(let j=0;j<old.length;j++){
   if(i===j)continue;

   const o=old[j];
   let [dx,dy]=wrapDistance(o.x-b.x,o.y-b.y);
   const d=Math.hypot(dx,dy);

   if(d===0)continue;

   if(o.type===b.type){
    // 同じ種族だけで群れを作る
    if(d<range){
     same++;
     ax+=o.vx;
     ay+=o.vy;
     cx+=dx;
     cy+=dy;

     // 近づきすぎない
     if(d<25){
      sx-=dx/(d*d);
      sy-=dy/(d*d);
     }
    }
   }else{
    // 違う種族とは少し距離を取る
    if(d<32){
     sx-=dx/(d*d)*1.8;
     sy-=dy/(d*d)*1.8;
    }
   }
  }

  let fx=0,fy=0;

  if(same>0){
   // 分離
   let s=limit(sx,sy,speed);
   fx+=s[0]*val("sep")*.10;
   fy+=s[1]*val("sep")*.10;

   // 整列：同じ色だけ
   let a=limit(ax/same,ay/same,speed);
   fx+=(a[0]-b.vx)*val("ali")*.075;
   fy+=(a[1]-b.vy)*val("ali")*.075;

   // 結合：同じ色だけ
   let c=limit(cx/same,cy/same,speed);
   fx+=(c[0]-b.vx)*val("coh")*.12;
   fy+=(c[1]-b.vy)*val("coh")*.12;
  }

  // エサを探す
  let nearest=null,nearestD=Infinity;

  for(const f of foods){
   const [dx,dy]=wrapDistance(f.x-b.x,f.y-b.y);
   const d=Math.hypot(dx,dy);
   if(d<nearestD){
    nearestD=d;
    nearest={dx,dy};
   }
  }

  if(nearest && nearestD<220 && nearestD>1){
   fx+=nearest.dx/nearestD*val("food")*.055*own.food;
   fy+=nearest.dy/nearestD*val("food")*.055*own.food;
  }

  // マウス誘導
  if(mouseMode && mouse.active && val("mousePower")>0){
   const [dx,dy]=wrapDistance(mouse.x-b.x,mouse.y-b.y);
   const d=Math.hypot(dx,dy);
   if(d<200 && d>1){
    fx+=dx/d*val("mousePower")*.06;
    fy+=dy/d*val("mousePower")*.06;
   }
  }

  // 滑らかな方向転換
  const f=limit(fx,fy,maxForce);
  b.vx+=f[0]*dt*60;
  b.vy+=f[1]*dt*60;

  const v=limit(b.vx,b.vy,speed*own.speed);
  b.vx=v[0];
  b.vy=v[1];

  const len=Math.hypot(b.vx,b.vy);
  if(len>.01){
   const newAngle=Math.atan2(b.vy,b.vx);
   let diff=Math.atan2(
    Math.sin(newAngle-b.angle),
    Math.cos(newAngle-b.angle)
   );

   // 大きな方向転換では古い軌跡を消す
   if(Math.abs(diff)>2.0){
    b.trail=[];
   }
   b.angle=newAngle;
  }

  b.x=(b.x+b.vx*dt*60+W)%W;
  b.y=(b.y+b.vy*dt*60+H)%H;

  // 軌跡
  if(trailMode && val("trail")>0){
   b.trail.push({x:b.x,y:b.y});
   while(b.trail.length>val("trail"))b.trail.shift();
  }else{
   b.trail=[];
  }
 });

 // エサの消費
 for(let i=foods.length-1;i>=0;i--){
  const f=foods[i];
  let eaten=false;

  for(const b of birds){
   if(!visible[b.type])continue;
   const [dx,dy]=wrapDistance(f.x-b.x,f.y-b.y);
   if(Math.hypot(dx,dy)<9){
    eaten=true;
    break;
   }
  }
  if(eaten)foods.splice(i,1);
 }

 // エサの再出現
 const target=val("foodNum");
 if(foods.length<target && Math.random()<.025*dt*60){
  createFood(Math.random()*W,Math.random()*H);
 }

 flockTotal=countFlocks();
}


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