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The physiological significance of biometric body condition indices (bBCI) is poorly understood. We hypothesized that bBCI are composite metrics of nutritional physiology, physical fitness and health. To test this hypothesis, we first compared the performance of eight bBCI, using 434 Southern European carnivores from six species as a model system; and then identified, by non-destructive methods, the hematology and serum biochemistry correlates of three selected bBCI. Fulton’s K Index, Major Axis Regression Residuals and Scaled Mass Index were the only bBCI insensitive to the effect of sex and age. The most informative physiological parameters in explaining the variation of these bBCI were the albumin (Effect Size (ES) = − 1.66 to − 1.76), urea (ES = 1.61 to 1.85) and total bilirubin (ES = − 1.62 to − 1.79). Hemoglobin and globulins (positive) and cholesterol (negative) were moderately informative (0.9, This work was supported by Junta de Comunidades de Castilla-La Mancha [Project PREG-05-23], Spanish Ministry of Science and Innovation and European Union-FEDER funds [Project CGL2009-10741]; Organismo Autónomo Parques Nacionales [Project OAPN352/2011]; Empreendimentos Eólicos do Vale do Minho S.A. and Associação para a Conservação do Habitat do Lobo Ibérico (ACHLI); Fundação para a Ciência e Tecnologia [grants SFRH/BPD/116596/2016 to N.S. and SFRH/BD/144087/2019 to M.N. and UID/BIA/50027/2019 to P.M.]; FCT/MCTES, through national funds, and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020 [cE3c—UIDB/00329/2020]; Juan de la Cierva research contracts from Ministerio de Ciencia e Innovación, Funder Id: 10.13039/501100004837 from the Spanish Ministry of Economy, Industry and Competitiveness [FJCI-2015-24949 to F.D.R.]; and the European Union H2020 [Project H2020 VACDIVA 862874 to J.A.B.].

Currently, there are naturalized populations of feral pigeon (Columba livia var. domestica) worldwide with an estimated global population between 165 and 330 million individuals. Feral pigeons are adapted to urban environments, creating problems related to human health, damage to architectural structures, unpleasant soiling, and foul odors. Thus, local governments usually implement measures to reduce feral pigeon populations in cities to a suitable size. We monitored a feral pigeon trapping campaign to investigate the use of cage traps as control method in residential zones. We analyzed efficiency (daily capture rate), effectiveness (defined as the number of feral pigeons captured relative to the total number of potential pigeon captures), animal welfare, selectivity (the proportion of captured feral pigeons in relation to the total number of captured animals), and the effect on feral pigeon abundance. All procedures were conducted in compliance with current European and Spanish legislation. Overall efficiency was 0.25 feral pigeons/trap-day, effectiveness was 22.5%, and selectivity was 99.7%. Over the study period, there was a decreasing trend in abundances. A significant decrease was found in the relative abundances of feral pigeons after 2 months of extractions, and population abundances remained low up to the end of the extraction period. The use of cage traps was a useful and effective method to reduce local feral pigeon populations in isolated urban areas with low building density in which the feral pigeon population has not yet reached high densities., F. Díaz-Ruiz was supported by a Juan de la Cierva postdoctoral contract (Ministerio de Ciencia e Innovación, Funder Id: 10.13039/501100004837, FJCI-2015- 24949) from the Spanish Ministry of Economy, Industry and Competitiveness.

How foraging behaviour of predators is influenced by prey abundance is often not clear. Predators may behave as generalist or specialist depending on the relationship between the predator feeding behaviour and prey abundance, known as functional response. The European rabbit (Oryctolagus cuniculus) is a key species for most Iberian vertebrate predators, especially for large raptors such as the eagle owl (Bubo bubo). The eagle owl functional response was analysed in central Iberian Peninsula by fitting different models (null, linear, two asymptotic and two sigmoidal models) between rabbit abundance and rabbit consumption by the eagle owl. Rabbit consumption increased as did its abundance until reaching an asymptote. Rabbit-consumed biomass better fitted to a type II functional response (convex, typical of specialist predators), whereas rabbit frequency in eagle owl diet better fitted to a type III functional response (sigmoidal, typical of generalist predators). Trophic diversity increased as rabbit abundance decreased. The consumption of other prey, such as Iberian hare (Lepus granatensis) and medium-size birds (mainly galliformes and columbiformes), increased as rabbit abundance decreased. The eagle owl is highly dependent on rabbits in central Spain, even at low rabbit abundance. In this situation, the eagle owl diversifies its diet, making it difficult to define the eagle owl as a specialist or as a generalist predator. Therefore, the eagle owl in the centre of the Iberian Peninsula should be rather considered as a facultative predator on wild rabbits., This study is a partial result of CGL2005–02340, CGL2009–10741, and CGL2013-43197 projects, from I+D National Plan funded by the Spanish Ministry of Science and Innovation and EU–FEDER funds. J. Fernandez-de-Simon benefitted from a FPI PhD scholarship (BES–2006–12562) funded by the Spanish Ministry of Science and Innovation and the European Social Fund. J. Fernandez-de-Simon and F. Diaz-Ruiz are currently holding a postdoctoral fellowship from Junta de Castilla-La Mancha and the European Social Fund (Operational Programme FSE 2007/2013).