Sometimes they get it from eating paint chips (particularly the light colors). More often they get it when you put out egg shells (saved after making breakfast) broken into tiny bits. Sometimes they get it from the extra calcium added to most types of suet.
If they don’t get the extra calcium they need at this time of year, their bodies take it from the birds’ bones, weakening them.
Rinse off any “slime” before storing shells and, before you put them out for birds, heat them to kill any remaining bacteria.
Stressed birds Cornell’s Lab of Ornithology reports that birds in cities often live more stressful lives than their rural relatives. Just think about it – lots of cats and dogs, lots of noise, lots of lights at unusual hours, pollution and parking lots instead of fields full of seed. Birds can usually adapt to city life, but are likely to have shorter life spans and fewer healthy offspring.