61 nests separated layer by layer

liningcupbaseHuman-made objects occurred most often in the base

20 more nests were inventoried whole. They counted toward the material totals, but not the layer comparison.

81nests inventoried across 88 breeding attempts
89%contained at least one human-made item
805plastic fragments counted, alongside other artificial materials
0.7%average share of nest mass made up by all human-made material

The inventory can show

  • what materials remained in a completed nest
  • how many pieces were present
  • where pieces lay in separable nests

It cannot recover

  • which available objects a bird rejected
  • whether each piece was deliberately preferred
  • whether the material caused breeding success