caa a22 4500 477090907 CHVBK 20180405111514.0 cr unu---uuuuu 170330e19960101xx s 000 0 eng 10.1007/BF01239352 doi (NATIONALLICENCE)springer-10.1007/BF01239352 Benkman Craig Department of Biology, New Mexico State University, 88003, Las Cruces, NM, USA aut Are the ratios of bill crossing morphs in crossbills the result of frequency-dependent selection? [Elektronische Daten] [Craig Benkman] Summary: The direction the lower mandible curves in crossbills (Loxia) is an example of a discrete polymorphism. The lower mandible crosses with equal frequency to the left and to the right in several crossbill populations. I hypothesize that the 1:1 ratio results from negative frequency-dependent selection favouring the rarer morph. A crossbill always orients toward closed conifer cones so that its lower mandible is directed towards the cone axis. Thus, only part of the cone can be reached easily when crossbills have few perch sites and the cone cannot be removed from the branch or otherwise turned round. Since crossbills may visit cones which have previously been foraged on by other individuals, an equal frequency of left-to-right mandible crossings may minimize overlap in the use of cones and enhance foraging efficiency. Experimental data support this hypothesis. Moreover, the variation in the ratio of mandible crossing directions among crossbill populations is consistent with this hypothesis. Chapman & Hall, 1996 conifer cones nationallicence crossbills nationallicence frequency-dependent selection nationallicence foraging behaviour nationallicence Loxia nationallicence polymorphism nationallicence Evolutionary Ecology Kluwer Academic Publishers 10/1(1996-01-01), 119-126 0269-7653 10:1<119 1996 10 10682 https://doi.org/10.1007/BF01239352 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF01239352 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Benkman Craig Department of Biology, New Mexico State University, 88003, Las Cruces, NM, USA aut NATIONALLICENCE 773 0- Evolutionary Ecology Kluwer Academic Publishers 10/1(1996-01-01), 119-126 0269-7653 10:1<119 1996 10 10682 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer