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Above all, bird ringing must be safe for birds, for ethical reasons but also to ensure that data collection is not biased by marking effects. Bird ringing schemes are responsible for determining the size of the rings used to mark birds individually. This paper critically reviews the recommended ring sizes in the Aranzadi Ringing Scheme and proposes an objective criterion for ringers. A morphological analysis of tarsus width (MTW) and the width of the tibia–tarsus articulation (MAW), over a sample of more than 4000 individuals of 74 species of both passerines and non-passerines captured in Spain, revealed that the mean difference between the internal diameter of the recommended ring (IDR) and MTW was 32% in relation to MTW (sd 15.8%, 95% confidence interval 28–35%). Experience demonstrates that this clearance is adequate, but recommendations for rings with clearances either too narrow (<6%) or too wide (>50–60%) should be reviewed and changed, if possible, to bring them closer to a 32% standard. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conducted a DFT study on C H activation catalyzed by [Fe(IV)O(n -TMC)(CH 3 CN)]2+ complexes with varying ring sizes (n = 12–16). • Macrocycles with larger ring sizes and the presence of an axial ligand show improved C H activation reactivity. • The reactivity is primarily influenced by the spin state energy difference and distortion energy. Here, a DFT investigation has been presented to demonstrate the relevance of the macrocyclic ligand ring size of the high-valent Fe(IV)O complex-catalyzed C H activation process. A nonheme iron-oxo compound bound with extensively studied macrocycle tetramethylcyclam (TMC) with varying ring size measures in terms of n = 12 , 13 , 14 , 15 , and 16 in [Fe(IV)O(n -TMC)(CH 3 CN)]2+ has been considered as the oxidant and dihydroanthracene as the general substrate. Counterions, as always, have been considered to avoid the self-interaction error in these DFT calculations. Computations were carried out to determine the effect of the axial ligand, acetonitrile, on the C H activation reactivity. It has been discovered that the complexes without axial ligands turned out to be more reactive compared to their axially coordinated counterparts. The most intriguing finding, however, has been that reactivity increased steadily with ring size increments, giving us the trend 12 < 13 < 14 < 15 < 16. Behind this typical pattern of reactivity, several factors played a role, including the energy of the electron acceptor orbital, which sequentially decreases, and the distortion energy to achieve the transition state, which also decreases as we move on from n = 12 to 16. The triplet-quintet energy difference of the oxidants also has a part to play, as it decreases with increased ring size, with the quintet becoming more and more dominant. The current studies have also been able to corroborate the experimental data that was published regarding Fe(IV)O(13 -TMC) (without axial syn form) having a higher C H activation reactivity than Fe(IV)O(14 -TMC) (with axial anti form). On the whole, this computational exploration gives us a reactivity pattern based on the ring size commutes and can lead to successful experimental results if pursued based on this reaction. [ABSTRACT FROM AUTHOR]