But the question remains: is the month's decline a blip -- or the start of a significant trend of Web visitors abandoning portal sites? Portals are vast collections of content offered by companies including Yahoo! Inc., Lycos and Go Network. It marks the first time that Web traffic researcher Media Metrix has reported a month-to-month dip in the total number of users tapping into the Internet's top-rated sites. The total number of unique visitors to the top 25 Web properties fell .4 percent to 64.97 million in April, down from 65.25 million in March. This according to a study of the top Media/Web properties at home and at work by Net research firm Media Metrix Inc. Web traffic to those sites had grown steadily in recent months. What's more, all but one of the top five sites lost traffic, the report said. Lycos was the biggest loser, falling 9 percent to 28.90 million unique visitors. American Online Inc., Yahoo! Inc., and The Walt Disney Co.'s Go Network also lost visitors. The only top-five property to gain traffic was Microsoft. Analysts attributed the flight from the major sites to a more sophisticated audience, and the beginning of daylight savings time. Television experiences a similar drop in viewership starting in the spring, as people in colder climates emerge from their houses and begin to spend more time outdoors. Analysts think the same trend is showing up on the Web. In addition, the Web audience has become more educated about the contents of the Internet. People don't automatically go to portal sites such as Yahoo! or AOL to find information, as they did in the old days. Instead they go directly to specific sites that meet their needs, such as those aimed at sports, travel, or women. "This doesn't mean people are abandoning the Web," said Allen Weiner, vice president of analysis at NetRatings Inc., which studies Web traffic. "We're beginning to see a more focused vision." In fact, several of the more vertical sites gained traffic from March to April. iVillage, women.com, Travelocity and Preview Travel saw big jumps during that time. Weiner said the trend toward narrower sites would continue into the future, and he said they could be more appealing to advertisers because they target a specific demographic. "We're going to see a whole new tier of portals," Weiner said. Clay Rider, an analyst at Zona Research in the U.S., also attributed the decline in traffic to tax time and the beginning of television sweeps. But he said a one-time decline shouldn't be cause for panic. "Unless it's a sustained, ongoing thing, we shouldn't worry," Rider said. "If we get fixated on the short term, we'll lose sight of what's important overall." With a difference so small, some Web publishers are likely to blame the dip on statistical vagaries in measuring audiences on the Internet. Methods that track usage by sample groups and use the data to project more broad audience totals have come under renewed scrutiny in the past month. A preliminary study released earlier this month by the Future of Advertising Stakeholders industry group indicated that sample measurements, such as those Media Metrix compiled, undercount traffic by as much as one-third when compared with traffic logged at the servers operated by large publishers. Audience measurement companies now are working with publishers to identify issues that may reconcile the differences between server log data and sample-based audience estimates. Steven Vonder Haar, Inter@ctive Week, contributed to this report