Subscribe to our newsletter

Electronics

Follow the Birds

What's the secret to piscatorial success?
Simple. Just follow the birds!

Terns and pelicans don't go fishing for fun. They do it because of their need to survive. And because they do it almost all day, every day, it stands to reason that they get pretty darn good at it.

Okay, I've never heard of a bird tackling a marlin or tuna—they're interested only in baitfish. But that's what the predator fish are interested in, too. So where you find birds, there's a good chance of finding fish.

The trouble is that even with good eyesight, you probably can't see a single bird much more than a couple of hundred yards away, and you'd be lucky to see a flock of them from half a mile or so. But radar can increase your bird-detection range by a factor of ten or more—and the area that you are scanning by a factor of a hundred!

Ten years ago, most people would probably have regarded the idea of looking for birds by radar as pure fantasy. Even now, with official advice telling us that we should all carry radar reflectors because our boats are too small to show up on ships' radars, it seems unlikely that something as small as a bird could possibly show up on a boat's radar.

But the plain fact is that they do.

One reason is because things that conduct electricity—like salt water—are generally good at reflecting radar energy. And birds, like all animals, are basically just little bags of salty water. Wet birds—ones that are actively fishing—are even better.

The other reason is that a radar pulse covers a fair amount of space. It's like a rather oddly shaped bubble, packed with radio energy, hurtling through the air at about a thousand million feet per second, and continuously expanding as it goes. By the time it has traveled a distance of six miles from the scanner, it measures about 1,000 feet from front to back, several hundred yards from side to side, and well over a mile top to bottom. A small object, such as a bird, occupies only a tiny fraction of this space, so it reflects only a tiny proportion of the energy contained in the pulse. But the pulse is plenty big enough to hit a whole flock of birds all at once. It would be oversimplifying things to suggest that two birds reflect twice as much energy as one bird, or that 100 birds reflect 100 times as much, but a flock of birds reflects a lot more energy than one bird, and can be seen at perhaps twice the distance.

It's much like rain clutter: one raindrop is far too small to produce a detectable echo, but a rain squall or thunderstorm is quite capable of producing such a strong echo that it will effectively obliterate sizable ships from the radar.

Almost any radar will detect heavy rain; in fact, it's such a nuisance that all radars come with a rain-clutter control to reduce the effect. But birds are more difficult: you need the right radar, carefully adjusted, if you hope to spot them at any useful distance.

The first and most fundamental requirement is power. Because individual birds are very small targets, and even a flock of birds occupies quite a small area when they are actively feeding, a low-power radar simply won't do the job; 4-kW is about the smallest unit that is really worth considering. And because the performance of any radar is enhanced if its power is focused into a nice, tight beam, most serious fishermen reckon it's best to leave radomes for the sailboaters and go for the largest open-array scanner their boat can manage.

With a 4-kW radar and a four-foot scanner, it's quite possible to pick out flocks of birds at up to four miles. Upgrade to a

6-kW radar with a six-foot scanner, and you're likely to be able to track flocks at six miles and locate individual birds at two or three miles. Upping the power to ten or twelve kilowatts won't double the range but you could well be able to locate flocks of birds at six to ten miles, and individual pelicans or frigate birds at four or five miles.

The other key requirement for an effective bird-spotting radar is a good display: the bigger and the higher-resolution the better. Color is almost standard, nowadays, and can be a real bonus when it comes to picking out bird flocks from background clutter.

But the performance of even the best bird-finding radar can be crippled if it is not set up right—and "right" for bird-finding is not quite the same as "right" for navigation or collision avoidance. The rain clutter or FTC controls, in particular, can be fatal to bird-spotting performance.

Start by switching the radar on and adjusting the brilliance, gain, and tuning as usual (or let the automatic tuning system do it for you). Then switch to manual mode, and start adjusting:

  • Set the range to three or four miles, or set the pulse-length control (if you have one) to "long."
  • Turn the gain up until the screen is entirely covered with a light background speckle.
  • Dial the sea and rain-clutter controls down to a minimum. If your radar has two rain-clutter controls (sometimes called "Rain" and "FTC") switch them both down or off.
  • Bird flocks should appear as small, dense patches of tiny echoes rather like miniature rain squalls. But if you have the option of color, use it. It is much easier to pick out a smudge of a different color than one of a slightly different density.
  • If you have the option of true motion, use it, and turn the "Trails" function on, to show whether the flock is moving. There's not much point in going after a flock that is moving, because it means its birds are hunting. Stationary flocks that have found fish and are feeding, so they will guide you to where the big ones are most likely to be biting.
  • This article originally appeared in the March 2010 issue of Power & Motoryacht magazine.

    Related Features