While morphological traits are often associated with multiple functions, it remains unclear how evolution balances the selective effects of different functions. Birds' beaks function not only in foraging but also in thermoregulating and singing, among other behaviours. Studies of beak evolution abound, however, most focus on a single function. Hence, we quantified relative contributions of different functions over an evolutionary timescale. We measured beak shape using geometric morphometrics and compared this trait with foraging behaviour, climatic variables and song characteristics in a phylogenetic comparative study of an Australasian radiation of songbirds (Meliphagidae). We found that both climate and foraging behaviour were significantly correlated with the beak shape and size. However, foraging ecology had a greater effect on shape, and climate had a nearly equal effect on size. We also found that evolutionary changes in beak morphology had significant consequences for vocal performance: species with elongate-shaped beaks sang at higher frequencies, while species with large beaks sang at a slower pace. The evolution of the avian beak exemplifies how morphological traits can be an evolutionary compromise among functions, and suggests that specialization along any functional axis may increase ecological divergence or reproductive isolation along others.

We designed a loop-gap microwave resonator for applications of spin-based hybrid quantum systems, and tested it with impurity spins in diamond. Strong coupling with ensembles of nitrogen-vacancy (NV) centers and substitutional nitrogen (P1) centers was observed. These results show that loop-gap resonators are viable in the prospect of spin-based hybrid quantum systems, especially for an ensemble quantum memory or a quantum transducer.Superconducting quantum circuits have been remarkably developed in the past decade, and are promising candidates for a quantum computer 1 . However, their decoherence times are relatively shorter than those of microscopic systems. Moreover, the low energy of microwave photons fundamentally prevents one from transferring quantum information processed in one superconducting quantum computer inside a dilution refrigerator to somewhere else outside of the millikelvin environment.Besides superconducting circuits, spins in solid crystals are another promising quantum system at microwave frequencies mainly because of their long decoherence times 2-7 . They are considered to be one of the ideal systems to build hybrid quantum systems 8-10 , where one can exploit both the good coherence of the spins and the designability and controllability of superconducting quantum circuits. It has been demonstrated that impurity spins in solid crystals are compatible with superconducting circuits: strong coupling with nitrogen-vacancy (NV) centers in diamond 11-16 , nitrogen (P1) centers in diamond 17,18 , rare-earth ions in optical crystals 19,20 , donors in silicon 21 , and magnons 22,23 have been demonstrated. The key to fully exploiting the long decoherence times of spins is the spin echo (refocusing) protocol, in which spins have to be inverted by a microwave pulse within a time scale of free induction decay 24-26 . However, in most previous works spins have not been uniformly driven because of the spacial inhomogeneity of the microwave magnetic fields in two dimensional resonator geometries [26][27][28] This has made it problematic to invert all the spins simultaneously. To circumvent this issue, some works using three dimensional microwave resonators have a) Electronic mail: yuimaru.kubo@oist.jp been reported [29][30][31][32][33][34][35] .Apart from the microwave aspect, many spin systems also possess optical transitions, which may be exploited to realize a quantum transducer, a device that coherently and bidirectionally converts between microwave and optical photons. Indeed, there have been several proposals to realize such a transducer using spins [36][37][38][39] . One of the crucial requirements of such a quantum transducer is an efficient mode-matching between microwave and optical resonators 36 . Here again, two dimensional superconducting resonators are not ideal to this end for two reasons: the inhomogeneous microwave magnetic field, and the superconducting gaps which have much less energy than optical photons.In this Letter, we design and test a loop-gap microwave resonator 40,41 , and show...

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