diff --git a/public/tide-pool-world.js b/public/tide-pool-world.js
index 22da2e7..5322cb1 100644
--- a/public/tide-pool-world.js
+++ b/public/tide-pool-world.js
@@ -19,7 +19,7 @@ export const SPECIES = {
   tab: { code: 'TB', name: 'Tab', kind: 'swimmer', speed: 1.05, max: 28, start: 12, min: 5, burn: .007, radius: .14 },
   pylon: { code: 'PY', name: 'Pylon', kind: 'sessile', max: 10, start: 4, min: 2, burn: .0025, radius: .3 },
   collector: { code: 'CL', name: 'Collector', kind: 'walker', speed: .95, max: 8, start: 3, min: 1, burn: .0035, radius: .38, core: true },
-  mason: { code: 'MS', name: 'Mason', kind: 'walker', speed: .58, max: 8, start: 3, min: 1, burn: .0045, radius: .4, core: true },
+  mason: { code: 'MS', name: 'Mason', kind: 'walker', speed: .58, max: 8, start: 3, min: 2, burn: .0045, radius: .4, core: true },
   breaker: { code: 'BR', name: 'Breaker', kind: 'walker', speed: .75, max: 6, start: 2, min: 1, burn: .0042, radius: .48, core: true },
   borer: { code: 'BO', name: 'Borer', kind: 'walker', speed: .32, max: 8, start: 4, min: 2, burn: .004, radius: .34 },
 };
@@ -465,10 +465,13 @@ function breed(world, c) {
   if (!canBreed(world, c.sp)) return null;
   const S = SPECIES[c.sp];
   let at = null;
-  for (let i = 0; i < 10 && !at; i++) {
-    const a = world.random() * Math.PI * 2, r = S.kind === 'sessile' ? 1.2 + world.random() * 1.4 : .5;
+  for (let i = 0; i < 16 && !at; i++) {
+    // A pylon's bud sometimes drifts far, like a spore, and settles in other standing water.
+    const far = S.kind === 'sessile' && world.random() < .45;
+    const a = world.random() * Math.PI * 2, r = S.kind === 'sessile' ? (far ? 5 + world.random() * 14 : 1.2 + world.random() * 1.4) : .5;
     const x = c.x + Math.cos(a) * r, z = c.z + Math.sin(a) * r;
-    const ok = S.kind === 'walker' ? onShelf(world, x, z) : depthAt(world, x, z) > (S.kind === 'sessile' ? .25 : .1);
+    const ok = S.kind === 'walker' ? onShelf(world, x, z) :
+      S.kind === 'sessile' ? depthAt(world, x, z) > .25 && world.S[cellAt(x, z)] > TIDE_LOW + .25 : depthAt(world, x, z) > .1;
     const clear = S.kind !== 'sessile' || world.creatures.every(o => o.sp !== 'pylon' || distance(o, { x, z }) > 1);
     if (ok && clear) at = { x, z };
   }
@@ -479,6 +482,7 @@ function breed(world, c) {
   child.angle = c.angle; child.heading = c.heading + (world.random() - .5) * 2;
   if (c.sp === 'tab') { child.vx = -c.vz; child.vz = c.vx; }
   if (c.sp === 'borer') child.home = settle(world, c) || child.home;
+  if (c.sp === 'collector' || c.sp === 'mason') child.home = roomy(world, child, 4, 12, c.sp === 'mason') || child.home;
   event(world, 'birth', c, null, label(child));
   return child;
 }
@@ -514,12 +518,15 @@ function think(world, c) {
 }
 
 function graze(world, c, efficiency = 1) {
+  // Good film, not too far, and not already crowded by others of the same kind. A few samples look much further afield.
   let best = null, score = -Infinity;
-  for (let k = 0; k < 14; k++) {
-    const r = k < 8 ? 3 : 9;
+  for (let k = 0; k < 16; k++) {
+    const r = k < 8 ? 3 : k < 13 ? 9 : 18;
     const x = c.x + (world.random() - .5) * r * 2, z = c.z + (world.random() - .5) * r * 2;
     if (!onShelf(world, x, z)) continue;
-    const s = world.film[cellAt(x, z)] - Math.hypot(x - c.x, z - c.z) * .04;
+    let crowd = 0;
+    for (const o of world.creatures) if (o !== c && o.sp === c.sp && Math.abs(o.x - x) < 2.5 && Math.abs(o.z - z) < 2.5) crowd++;
+    const s = world.film[cellAt(x, z)] - Math.hypot(x - c.x, z - c.z) * .025 - crowd * .12;
     if (s > score) { score = s; best = { x, z }; }
   }
   assign(world, c, 'graze', null, { at: best || { x: c.x, z: c.z }, patience: 14 });
@@ -616,14 +623,16 @@ function thinkMason(world, c) {
     const spot = ringSpot(world, c);
     if (spot) return assign(world, c, 'build', null, { at: spot, patience: 50, reach: .45 });
     // The home is finished: start another nearby, on ground that is neither built nor deep.
-    const next = { x: c.home.x + (world.random() - .5) * 6, z: c.home.z + (world.random() - .5) * 6 };
-    c.home = onShelf(world, next.x, next.z) ? next : { x: c.x, z: c.z };
+    c.home = roomy(world, c, 3, 12, true) || { x: c.x, z: c.z };
     event(world, 'home', c);
     return idle(world, c);
   }
-  if (c.energy < .4) return graze(world, c);
-  if (c.energy > .8 && canBreed(world, 'mason')) {
-    const source = brassSource(world, c, world.random() < .5);
+  // Once hungry, a mason keeps feeding until it is properly full, which leaves it strong enough to breed.
+  if (c.energy < .4) c.hungry = true;
+  if (c.energy > .85) c.hungry = false;
+  if (c.hungry) return graze(world, c);
+  if (c.energy > .7 && canBreed(world, 'mason')) {
+    const source = brassSource(world, c, world.random() < .55);
     if (source) return assign(world, c, source.steal ? 'steal' : 'fetch', source.object, { use: 'breed' });
   }
   if (c.energy > .45 && ringSpot(world, c)) {
@@ -641,7 +650,7 @@ function thinkBreaker(world, c) {
     const source = brassSource(world, c, true);
     if (source) return assign(world, c, source.steal ? 'steal' : 'fetch', source.object, { use: 'breed' });
   }
-  if (c.energy < .92) {
+  if (c.energy < .7) {
     const target = nearest(c, world.creatures.filter(s => s.sp === 'scraper' && s.shell === null), 28);
     if (target) {
       // Prey inside a wall: break the wall down first.
@@ -682,6 +691,23 @@ function nearbyWater(world, c, radius = 14) {
   }
   return best;
 }
+// Somewhere to settle: on the shelf, clear of others of the same kind, and near water other than the crowded first pool when possible.
+function roomy(world, c, r0, r1, wantWater) {
+  let best = null, score = -Infinity;
+  for (let k = 0; k < 24; k++) {
+    const a = world.random() * Math.PI * 2, r = r0 + world.random() * (r1 - r0);
+    const x = c.x + Math.cos(a) * r, z = c.z + Math.sin(a) * r;
+    if (!onShelf(world, x, z) || z > 10) continue;
+    let near = 99;
+    for (const o of world.creatures) if (o !== c && o.sp === c.sp && o.home) near = Math.min(near, distance(o.home, { x, z }));
+    let wet = 0;
+    for (let n = 0; n < 6; n++) { const b = n / 6 * Math.PI * 2; if (depthAt(world, x + Math.cos(b) * 2, z + Math.sin(b) * 2) > .15) wet++; }
+    const first = bodyAt(world, x, z) === 'I';
+    const s = Math.min(near, 8) + (wantWater ? wet * .8 : 0) - (first ? 4 : 0) - (depthAt(world, x, z) > .5 ? 3 : 0);
+    if (s > score) { score = s; best = { x, z }; }
+  }
+  return best;
+}
 // A new burrow site: dry shelf a fair walk from any standing water, so its burrow starts a pool of its own.
 function settle(world, c) {
   for (let k = 0; k < 30; k++) {
@@ -953,6 +979,12 @@ function moveSwimmer(world, c, dt) {
     }
     if (best > depth) { ax += bx * 2.5 * worry; az += bz * 2.5 * worry; }
   }
+  // At high water the school roams the flooded shelf along a slowly turning heading.
+  const high = tideOf(world.time);
+  if (high > .55 && depth > .15) {
+    c.heading += (world.random() - .5) * dt * 1.2;
+    ax += Math.cos(c.heading) * 1.4 * (high - .55) * 2.2; az += Math.sin(c.heading) * 1.4 * (high - .55) * 2.2;
+  }
   const a = (world.random() - .5) * 2.2;
   ax += Math.cos(c.phase * .3 + a) * .5; az += Math.sin(c.phase * .3 + a) * .5;
   c.vx += ax * dt; c.vz += az * dt;
diff --git a/public/tide-pool.js b/public/tide-pool.js
index 323a921..4de7a05 100644
--- a/public/tide-pool.js
+++ b/public/tide-pool.js
@@ -1,7 +1,7 @@
 import {
   createWorld, advanceWorld, offerObject, SPECIES, SPECIES_ORDER, CELL, COLS, ROWS, X0, Z0, X1, Z1, START_POOL, waterLevel, daylight,
   heightAt, surfaceAt, depthAt, onShelf, bodyAt, tideOf, tideRising, label, goalText, describeWorld, creatureById,
-} from './tide-pool-world.js?v=8';
+} from './tide-pool-world.js?v=9';
 
 const root = document.querySelector('[data-tide-pool]');
 const status = document.querySelector('#tide-status');
diff --git a/scripts/tide-pool.test.mjs b/scripts/tide-pool.test.mjs
index 3eaf822..6e08270 100644
--- a/scripts/tide-pool.test.mjs
+++ b/scripts/tide-pool.test.mjs
@@ -166,8 +166,11 @@ test('pylons fold shut when the water is disturbed and reopen once it is still',
   dropObject(world, 'pebble', pylon.x + .3, pylon.z);
   run(world, 1);
   assert.ok(pylon.open < .3, `open ${pylon.open}`);
+  // Leave it alone: no one else nearby to disturb the water.
+  world.creatures = [pylon];
+  world.ripples = [];
   run(world, 15);
-  assert.ok(pylon.open > .6 || depthAt(world, pylon.x, pylon.z) < WET);
+  assert.ok(pylon.open > .6 || depthAt(world, pylon.x, pylon.z) < WET, `open ${pylon.open}`);
 });
 
 test('a runaway shelf stays bounded: no ground below the digging floor and all water finite', () => {
diff --git a/src/components/tide-pool.tsx b/src/components/tide-pool.tsx
index bef8bf1..d613b3a 100644
--- a/src/components/tide-pool.tsx
+++ b/src/components/tide-pool.tsx
@@ -138,7 +138,7 @@ export function TidePoolContent() {
         <p id="tide-description" role="status"></p>
         <p>Rendered with Three.js. <a href="/public/tide-pool-three-license.txt">Software license</a>.</p>
       </details>
-      <script type="module" src="/public/tide-pool.js?v=11"></script>
+      <script type="module" src="/public/tide-pool.js?v=12"></script>
     </main>
   );
 }