You can make a statement and put the citation(s) at the end of the sentence:
The Ecstatic Display calls of individual Adélie penguins are distinctive (Ainley, 1975; Jouventin, 1982).
You can incorporate the citation(s) in the body of the text:
According to Ainley (1975) and Jouventin (1982), the Ecstatic Display calls of individual Adélie penguins are distinctive.
When listing two or more citations, list them in chronological order (ie, by year), divided by a comma or semicolon, eg, (Burns & Leathwick, 1996; Rebertus & Burns, 1997; Burns et al., 2000; Pezzo et al., 2001; Neale, 2010).
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If the source has two authors, name them both, eg, (Whitaker & Edwards, 2010) or (Shuttleworth & Johnson, 2010). If there are three or more authors, name the first and then write et al. - an abbreviation of the Latin et alia, meaning “and others”. Make sure et al. is italicised and that there is a full stop after al., eg, (Hegland et al., 2009)
If you are using two or more sources by the same author in the same year, give alphabetical annotations, e.g. (Marks et al., 2010a), in the order you cite them in your text. If citing two or more sources by the same author in a single citation, you can give the author’s name once with the dates of all the sources, but this is not essential e.g. (Marks et al., 2010a, 2010b).
If you are citing material that is in the process of being published, cite it as in press (eg, (Carere et al., in press)).
Generally you should avoid citing webpages, but you may need to cite a webpage that provides data, a key, or software you have used in your analyses. For example, in a study surveying for insects in native grasslands you may need to cite some online keys used in identification (AllanHerbarium, 2000; Ford et al., 2009), and freeware used for statistical analyses (Hammer et al., 2001). See the APA style guide for more examples of citing electronic sources.