Nesting cavities are often a limited resource that multiple species use. There is an ongoing discussion on whether invasive cavity nesting birds restrict the availability of this key limited resource. While the answer to this question has important conservation implications, little experimental work has been done to examine it. Here, we aimed to experimentally test whether alien cavity nesting birds affect the occupancy of cavities and the resulting breeding success of native cavity breeders in a large urban park located in Tel Aviv, Israel. Over three breeding seasons, we manipulated the entry size of nest boxes and compared the occupancy and breeding success of birds in nest boxes of two treatments. These included nest boxes with large-entrance and small-entrance holes. The large-entrance holes allowed access for both the native and invasive birds (the two main aliens in the park are the common mynas and rose-ringed parakeets). The smaller-entrance boxes, on the other hand, allowed only the smaller sized native cavity breeders (great tits and house sparrows) to enter the boxes but prevented the alien species from entering. We found that the large-entrance nest boxes were occupied by five different bird species, comprising three natives (great tit, house sparrow, Scops owl) and two invasive species (common myna, rose-ringed parakeet) while the small-entrance boxes were only occupied by the two native species. The alien common mynas and rose-ringed parakeets occupied 77.5% of the large-entrance nest boxes whereas native species, mainly great tits, occupied less than 9% of the large-entrance boxes and 36.5% of the small-entrance boxes. When examining the occupancy of those cavities that were not occupied by the aliens, natives occupied both the small and large-entrance nest boxes equally. Three quarters (78%) of the great tits breeding in the large-entrance boxes were usurped by common mynas during the breeding season and as a result breeding success was significantly lower for great tits breeding in the large-entrance boxes compared with the small-entrance boxes. The results of this study suggests that the invasive alien species can reduce the breeding potential of native cavity breeders both by exploiting the limited breeding resource (nest cavities) and by directly usurping cavities already occupied by the native species. Since the majority of large-entrance nest boxes were occupied by the larger alien birds, less native species bred in the limited number of unoccupied large-entrance nest boxes because of exploitation competition. We propose that for management purposes, nest-box programs that alter the entrance size of available natural cavities may be a practical approach, reducing the competition between native cavity breeders and alien invasive birds, and especially benefiting the smaller native cavity breeders.

Birds Concealed sex Cooperalively breeding spccies Human sexual behaviour Tactical deception Coope.ration•Maintenance hypothesisStriking uniformity exists in humans' preference to conceal sexual activity from conspecifics' view. Yet, little is known about the selective pressures acting upon its evolution. To investigate rhis question, we srudied the cooperatively breeding Arabian babbler (Turdoides squamiceps), which has been suggested being the only olher species where dominant individuals conceal sex regularly. We examined whelher birds indeed conceal sex and tested different hypolheses postulating Lhat sex concealment functions to avoid prcdators, signal dominance status, or to avoid social interference. The results showed Lhat the birds concealed sex in all observed cases of copulation, did not prefer to copulate under shelters and concealed mating solicitations from adult conspecifics.In addition, subordinates did not attack dominants who courted the respective female. Hence, none of the tested hypotheses explains these resul ts satisfactorily. We posrulare rhat dominant Arabian babblers conceal sex ro maintain cooperation wilh those helpers they prevent from mating. Empirical desiderata for testing this 'Cooperation-Maintenance' hypothesis are discussed.

Intentional signalling plays a fundamental role in human communication. Mapping the taxonomic distribution of comparable capacities may thus shed light on the selective pressures that enabled the evolution of human communication. Nonetheless, severe methodological issues undermine comparisons among studies, species and communicative modalities. Here, we discuss three main obstacles that hinder comparative research of 'first-order' intentional signalling (i.e. voluntary signalling in pursuit of a cognitively represented goal): (i) inconsistency in how behavioural hallmarks are defined and operationalised, (ii) testing of behavioural hallmarks without statistical comparison to control conditions, and (iii) bias against the publication of negative results. To address these obstacles, we present a four-step scheme with 20 statistical operational criteria to distinguish between non-intentional and first-order intentional signalling. Our unified scheme applies to visual and audible signals, thereby validating comparison across communicative modalities and species. This, in turn, promotes the generation and testing of hypotheses about the evolution of intentional communication.