Baseball’s general managers are a canny bunch, as aware of each other team’s rosters and needs as they are of their own.

His rival GMs know when their cell phone rings and Dave Dombrowski’s name flashes that the Tigers front-office chief is hunting for a relief pitcher ahead of the July 31 (non-waiver) trade deadline.

On the flip side, Dombrowski realizes the Astros are looking for pieces they can meld with a heavy rebuilding project. The Brewers, Padres, and Rockies, he knows, could be open to broad trade options. And, if decisions go the way the Tigers and other serious contenders hope, the Giants might be persuaded to wash their hands on 2013 and make available some helpful relievers as they look ahead to better, sturdier years.

Dombrowski’s motivation is plain to anyone who has followed a first-place team that has an ongoing headache. Tigers relievers are 22nd in earned-run average (3.93) among 30 big league teams. They have allowed the sixth-most hits. They have doled out the seventh-most walks.

In short, Tigers back-end pitchers have not matched Detroit’s starters, whose earned-run average (3.73) is tops in the American League, and whose WHIP (walks plus hits per inning) is second in the American League to the A’s.

For a team with a nervous 1½-game lead over the Indians in the American League Central, and for a defending American League champion with thoughts of winning through three rounds of October’s playoffs, there is virtually zero chance Dombrowski will ride with his current relievers mix when they pitched as erratically as they did during the 2013 season’s first 94 games.

Not that Dombrowski is sanctioning any thoughts there.

“We are all aware the trading deadline is July 31st,” Dombrowski wrote Wednesday in an email response to a question about Detroit’s bullpen considerations, “and we will continue to keep a pulse on other club’s needs and what players may be available.”

In other words: It does no good for Dombrowski to amplify to the public and to the marketplace the Tigers’ obvious soft spots. Rather, in Dombrowski’s view, it makes a tense July — and trade negotiations that with any club will be a tightrope walk — more strenuous and complicated.

Weeks ago, Dombrowski knew his bullpen could become a Waterloo every bit as much as hitters in manager Jim Leyland’s lineup who weren’t cooperating. Victor Martinez’s bat has since heated up, which has helped the offense bountifully, but the Tigers bullpen remains a hot-and-cold region where performances fluctuate and roster names come and go based on what’s happening in Detroit and at Triple A Toledo.

The Tigers’ root problem might be traced to April 19, in a game against the Angels at Anaheim, Calif. Octavio Dotel was ripped for four hits, a walk and five runs in a ghastly appearance that lasted two-thirds of an inning.

A day later, Dotel was shipped to the disabled list with elbow inflammation. There appears little chance he will make it back in 2013.

Next to fall was Brayan Villarreal, a strikeout reliever who couldn’t seem to locate home plate and whose wildness earned him a ticket to Toledo, where the control struggle continues.

Al Alburquerque contributed to a general back-end failure that put him on I-75 for the one-hour trek to Toledo. He has since been recalled, as has his off-and-on relationship with the strike zone.

This was separate from the Tigers’ long and storied search for a closer, which endured its share of bad times (Bruce Rondon’s wobbly ways in spring camp, Jose Valverde’s implosion later in the spring) ahead of Joaquin Benoit arriving — for now — as the Tigers’ most reliable option.

The above cast, all right-handers, has been matched for sheer stressfulness by left-hander Phil Coke (5.83 ERA), not to mention Darin Downs, another left-hander, whose ERA soared to 5.18 ahead of his July 7 march to the disabled list.

It leads to a simple conclusion, based not only on the above numbers, but on Dombrowski’s knack for diagnosing a problem and moving aggressively to cure it.

The Tigers GM will be offering farm prospects, and perhaps an existing roster player or two, in exchange for a reliable right-handed reliever and, very likely, for a left-hander, as well.

The Tigers have trade chips. But they hope to hang onto the very best of those chips, beginning with Nick Castellanos, who would be traded only in the event Dombrowski comes across a mega-package the Tigers find irresistible.

That’s unlikely to happen, particularly in July, when the Tigers are more likely to make smaller deals that keep safe their best young talent: Castellanos, infielders Eugenio Suarez and Harold Castro, pitchers Jake Thompson and Endrys Briceno, outfielder Danry Vasquez, etc., all of whom are probably on that Not Likely Available list.

The Tigers could, conceivably, be coaxed into parting with outfielder Avisail Garcia, even if they envision him replacing Torii Hunter when Hunter’s contract expires 15 months from now. It is also possible the Tigers could make available Andy Dirks, given that Castellanos is working in left field at Triple A Toledo and is approaching a call-up.

But the Tigers will want more time analyzing the Dirks-Castellanos issue when Dirks has a heavy track record (.293 batting average entering 2013) and when his range in left field has been a major plus for the Tigers. Those attributes should cancel any notions of a Dirks deal, particularly when the Tigers no doubt believe they can find their bullpen arms minus dealing a royal-blue prospect or an important existing roster player.

Who will the Tigers hunt as Dombrowski’s July safari presses on?

Even if teams on the fence about selling parts — the Giants, Phillies, Jays, for example — decide not to offer relievers ahead of July 31, Dombrowski is a good bet to repeat past July habits and pilfer a right-hander, left-hander, or both, from a long list of marketable pitchers.

That means a right-hander such as Steve Cishek of the Marlins, or Francisco Rodriguez of the Brewers, could be on Dombrowski’s favorites list, as well as another Brewers right-hander, John Axford. He might bid on the Mariners’ Tom Wilhelmsen, given Dombrowski’s trade past with Seattle’s Jack Zduriencik.

The Brewers will be a percentage favorite to send at least one reliever to the Tigers, especially when left-hander Tom Gorzelanny is a DNA match for Detroit’s back-end needs. Mike Dunn (Marlins), Oliver Perez (Mariners), or even Wesley Wright (Astros) could likewise have a place high on Dombrowski’s docket.

The x-factor is San Francisco. The Giants have inventory galore — if Brian Sabean decides the future isn’t now, it’s in 2014 and beyond, as he ponders selling off Javier Lopez, Jose Mijares, or (gasp) Tim Lincecum.

Lincecum nearly became Tigers property in 2006 when the Tigers considered drafting him in the first round, at No. 6 overall, where they instead took Andrew Miller. Lincecum went to the Giants at No. 10, and it’s possible that draft day wasn’t the only occasion the Tigers were interested in Lincecum.