When passing more than one trailing throwable: 

Logger logger = LoggerFactory.getLogger(Main.class);
logger.warn("Message1={}, message2={}.", 
        new Exception("I'm ex1"), 
        new Exception("I'm ex2"), 
        new Exception("I'm ex3"));

Output:

12:28:09.687 [main] WARN ch.qos.logback.classic.Main - Message1=java.lang.Exception: I'm ex1, message2={}.
java.lang.Exception: I'm ex3
at ch.qos.logback.classic/ch.qos.logback.classic.Main.main(Main.java:10)

The second exception is trimmed by MessageFormatter#arrayFormat(String, Object[]) in LoggingEvent#getFormattedMessage(), although throwable had been already extracted in constructor.