What was done
Using bird-ringing records covering a time span of 41 years (1964-2004), the authors "documented shifts in the timing of breeding and brood size in a long-distance migrant, the Red-Backed Shrike (Lanius collurio) from a central European population," after which they compared their results with the climatic history of the region over the same time period.

What was learned
Husek and Adamik report that "temperatures in May significantly increased" over the period of their study; and they say that "in line with this increasing May temperature" there was "a 3- to 4-day shift towards earlier breeding," which pattern, in their words, "is consistent with the results of similar studies on other long-distance migrating songbirds (e.g., Dunn, 2004)." In addition, they report there was "an increase in brood size by approximately 0.3 nestlings since 1964."

What it means
The two researchers state that "given that early broods are usually larger (Lack, 1968; this study) and that they have a higher nest success (Muller et al., 2005), this may have a positive effect on future population increases as the temperature continues to rise."

References
Dunn, P. 2004. Breeding dates and reproductive performance. Advances in Ecological Research 35: 69-87.

Lack, D. 1968. Ecological Adaptations for Breeding in Birds. Methuen, London.

Muller, M., Pasinelli, G., Schiegg, K., Spaar, R. and Jenni, L. 2005. Ecological and social effects on reproduction and local recruitment in the red-backed shrike. Oecologia 143: 37-50.