In summary, we have shown that Pyk2 is not required in osteoblasts for the immediate mechanical response to short periods of FF. Unlike FAK deficient osteoblasts, Pyk2 deficient osteoblasts exhibit appropriate increased c-Fos and COX-2 protein levels, increased OPN expression and increased ERK phosphorylation in response to FF. These data are the first to indicate that FAK and Pyk2 have non-overlapping functions during osteoblast mechanotransduction. Additionally, we have demonstrated that the orbital platform method of generating FF is similar to the oscillatory pump method in both primary and immortalized calvarial osteoblasts as measured by these immediate early responses. In most songbird species, males exhibit a song repertoire of variable size and composition, which has been shown to play a crucial role in female attraction and/or territorial defence. Interspecific differences in repertoire size are mainly mediated by a large diversity of song-learning programmes that determine when the songs are learnt and for how long the song repertoire is modified. The duration of the sensitive period for memorizing songs varies from a month during the first months of life to throughout life. Bird species that learn the songs during a limited short period early in life and do not change their crystallized repertoire as adults are known as closed-ended learners. On the other hand, species that are able to add new songs during adulthood are classified as open-ended learners. Establishing whether a species is closed- or open-ended is important to enable interpretation of functional or evolutionary consequences of variation in repertoire size. For instance, song learning in openended learners may allow song repertoire to serve as a more immediate indicator of a male’s condition, and not just as an indicator of his condition as nestling or young fledgling. In order to establish unambiguously whether a songbird can memorize new songs during adulthood, controlled laboratory experiments are necessary. However, social and ecological factors that are not present during laboratory experiments may provide key variables for the understanding of birdsong learning. Therefore, field studies could offer an alternative approach to enable us to establish when birds memorize their repertoires. One of the main difficulties in identifying a species as an age-limited or open-ended learner under field conditions is the labour-intensive method of documenting full song repertoires in multiple years or after experimental treatment. In addition, since field studies cannot provide the experimental control of laboratory studies, it is important to use individually marked birds under a common and standardized recording protocol. The difficulty in establishing the timing of song repertoire learning in wild populations can be well illustrated using the great tit. Although this species was initially classified as a closed-ended learner, some XAV939 evidence suggests.