With the holiday shopping season behind them, retail mobile sites got back to business as usual in the first quarter of 2015. 

While big holiday sales, corresponding promotional messages and advertisements tend to drive average mobile page weight up in the fourth quarter, one would expect to see retail mobile sites slimming down in the subsequent first quarter.

However, in first-quarter 2015 retailers actually increased the average byte size of their mobile sites by 9 percent. Not surprisingly, retailers saw a slight uptick in their average mobile Web page load time, rising 3.4 percent from 2.06 seconds to 2.13 seconds. 

It is a basic rule of Web performance that, all things being equal ? i.e. optimization techniques or server ? a heavier page will take longer to load than a lighter one.

Sears and Macy?s topped the list of retail mobile site performers for the second straight quarter in both page speed and availability. 

In the case of Sears, its success resulted from the fact that during the measurement period, it delivered the lightest page by far at fewer than 60K downloaded bytes. Grainger was the second lightest at 108K. 

In fact, the four fastest sites all claimed the same spots as they did in fourth-quarter 2014, with the one newcomer to the top five being Gap, which ousted Office Depot.

Top performers (mobile Web page load time):

1. Sears

2. Macy?s

3. Bloomingdale?s

4. Grainger

5. Gap

After trailing the retail mobile sites in Web page load time in the fourth quarter, the banking index was significantly faster than retail in the first quarter, improving the average load time from 2.12 seconds to 1.99 seconds ? a 6 percent drop.

Like the retail sites, the average banking mobile homepage actually saw a slight rise in the amount of bytes they delivered, indicating that these companies have worked to improve their performance optimization techniques.

Citizens Bank once again led the way with a median mobile Web page load time of less than a second ? 0.76 seconds, to be precise ? and was one of five sites to register an availability ranking more than 99.9 percent. 

And like last quarter, some of the banking mobile sites registered a high number of objects on the page. 

Excessive objects can often lead to failures if one or more of them has problems loading, so it is not surprising that the three sites with more than 50 objects each also registered the three lowest availability scores. 

TD Bank is a case in point, since the number of objects and bytes on its mobile homepage went up in the first quarter, and their availability dropped to an unacceptable level of 95.6 percent.

Top performers:

2. U.S. Bank

3. Chase

4. Citibank

5. Wells Fargo

The travel site index came in with the slowest average mobile Web page load time for the third straight quarter at 2.36 seconds, owing in large part to the fact that mobile travel sites tend to be highly feature-rich, with numerous high-res photos to advertise destinations. 

Even so, that number was dramatically affected by one airline?s site that registered a median time of 5.22 seconds when no other site even reached the four-second mark. 

Google Flights provided the fastest mobile Web page load times as well as a perfect 100 percent availability score, but right behind it in second place was the airline ticketing site Kayak, which was just one-tenth of a second slower. 

Kayak also had the third-best availability rating at 99.95 percent despite it being the ninth-smallest site, so clearly Kayak has developed a masterfully efficient performance strategy rivaling that of Google.

Also showing a commitment to performance are TripAdvisor and Southwest Airlines. 

TripAdvisor?s wide array of travel-related services means that its homepage was among the heaviest of the sites tested, but with just 24 objects on the page, it is also in the top five in terms of both mobile Web page load time and availability. 

Southwest has gone a different route, offering a mobile homepage that is a third the size as TripAdvisor, but with a few more objects. The result is roughly the same though, as Southwest also registers top-five scores in both categories.

Top performers:

1. Google Flights

2. Kayak

3. TripAdvisor

4. Southwest

5. JetBlue

Light sites with fewer objects on the page are usually the best way to ensure fast Web page load times and high availability for both desktop and mobile sites. 

And with Google potentially valuing mobile page speed more than before with their new search algorithm in addition to mobile-friendly site design, a fast user experience could soon have an even more dramatic effect on how sites fare in mobile search rankings.

Therefore, IT operations professionals should be doing everything that they can to improve their mobile site performance. 

That means shrinking the number of bytes, objects and third parties on the homepage as much as possible, and employing the latest performance optimization techniques as well as a comprehensive monitoring strategy. 

Doing so should have marked effects on both mobile site performance as well as the company?s bottom line.