HP and infection: To test whether increased reproductive effort affected the response to infection, we enlarged blue tit Cyanistes caeruleus broods (c.f. García‐Navas & Sanz, 2010; Nur, 1984), subjected the breeding females to a mimicked bacterial infection (using lipopolysaccharide; henceforth LPS) and measured subsequent feeding frequency, body temperature and haptoglobin concentration.