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. 2013 Sep 18;8(9):e75536. doi: 10.1371/journal.pone.0075536

Figure 2. Mean first egg dates for great tits and blue tits at Cambridge University Botanical Gardens (green), Cow Lane Nature Reserve (blue) and Brampton Wood Nature Reserve (red) between 2003 and 2012.

Figure 2

Symbols for 2012 are also marked (×). The warmth sum index is the sum of maximum daily temperatures from 1 March-25 April (see McCleery and Perrins 1998).