As a postdoc, should I expect my PhD adviser to fund my conference travel to present my PhD work?

One should always figure out the funding issues before submitting an abstract to a conference. Presenters withdrawing from a conference are a major headache to the conference organizers and it is unreasonable to expect them to reorganize the conference program because you did not figure out your travel plans (either timing or funding) in advanced. There are cases where there is nothing you can do (e.g., having a child), but in general when you submit an abstract you are committing yourself to presenting the work.

As to who should fund your travel, the best would have been to ask when you submitted to the conference. There really isn't a standard for who should pay. The first issue is to determine if your PhD advisor or Post Doc Advisor has money that could be used to pay for your travel. They would have to have money that could, if they desired, be used to fund your travel, and be willing to fund your travel.

I would ask both people and see what they say. No one is going to be offended by you asking. I wouldn't be surprised if both said no, but nor would I be surprised if both said yes.

You might see if there are other sources of funding available from your current university. Commonly they do have some travel funding available for their researchers who don't have grant money, and you might be eligible. It might not cover everything, or there might be some sort of competitive application process, but it is worth checking. It may be administered through a unit called "Office of Research" or something like that.

In my field it's pretty common for postdocs to be allotted some funding of their very own from the university, that they can spend on travel, etc. I assume if you had this, you wouldn't be asking the question, but it's just possible that if you didn't read fine print, you might have overlooked it.

As a PhD student, I disagree with some of the advice here. Students (and post doctoral fellows) can be pressured by their university/advisor to publish and present at conferences. At my university there were specific PhD sub Courses that had to be complete and this involved presenting at different level conferences. So essentially, you needed to at least submit papers to these conferences or else you would not get your PhD. In my case, I applied (submitted a paper) to an international conference and my paper was accepted. I soon wished it wasn't because my university did not cover all costs and going would cut into my own funds by about 1000 dollars. Do not blame students for backing out or for 'disrupting' a presenter list when the universities themselves often do not tell the students what 'conference travel' entails. To the person saying to sleep on floors etc, NO. Students should be able to say "i do not wish to go" without ANY PENALTY. simple.