Nest Wishes - Why Birds Need Calcium — And How We Can Help Them Get It

Calcium is one of the most important nutrients for birds, especially during nesting season. More than one‑third of an adult bird’s total mineral content is calcium, and about 98% of it is stored in the skeleton. Even though birds are much lighter than mammals, the proportion of their body weight made up of bone is surprisingly similar.

Why Calcium Is So Challenging for Birds

  • Calcium is the hardest mineral for birds to maintain because:
  • Their needs swing dramatically during egg laying and chick development.
  • Many natural foods — especially seeds and insects — are too low in calcium to meet these demands.
  • Birds laying more than 2–3 eggs must significantly increase their calcium intake on the days they produce shells.

Without enough calcium, birds struggle to reproduce successfully:

  • Adult birds may lay fewer eggs.
  • Eggs may have thin shells, causing embryos to dry out.
  • Adults may pull calcium from their own bones, leading to weak, porous skeletons.
  • Chicks can develop rickets, lameness, painful joints, and misshapen bones.

How Birds Seek Out Calcium

Birds instinctively look for calcium-rich foods, especially in the evening, when females are forming the next day’s eggs. If given two foods identical except for calcium content, egg‑laying females and chicks will choose the calcium‑rich option.

Natural calcium sources vary by habitat and may include:

  • Snail shells
  • Insect exoskeletons
  • Bones (often fish bones)
  • Ashes
  • Calcium-rich soil
  • Eggshells from earlier-nesting birds
  • Even mortar from buildings

But these sources are inconsistent — especially from March through July, when most backyard birds are nesting.

How Wild Birds Unlimited Helps: Added Calcium in Our Foods

To support birds during their highest‑need seasons, many Wild Birds Unlimited foods include added calcium carbonate — the same mineral form found in limestone. It breaks down quickly in the digestive tract, making it easy for birds to absorb and use immediately.

WBU Foods with Added Calcium:

  • SuperSuet cakes, no-melt cakes, hot pepper cakes
  • SuperSuet no-melt cylinders, hot pepper cylinders
  • SuperSuet no-melt plugs
  • PB&J Suet no-melt cake
  • Nesting SuperBlend (bag, cylinder, hot pepper cylinder)
  • Bluebird Bugberry Blend
  • Bark Butter (regular and hot pepper)
  • Bark Butter Bits (regular and hot pepper)
  • Bark Butter no-melt cakes (regular and hot pepper)
  • TreeNutty Plus Blend
  • Choice Plus Blend
  • White Deluxe Plus Blend
  • No-Mess Plus Blend