Dew point: the race weather that temperature alone does not reveal

Güvercin Yeri · Updated: October 15, 2026 · About 8 min read

When we look at the weather on a race or training day, most of us check the temperature, the wind and the chance of rain. Yet two days with the same temperature can be very different for the birds. There is a value that helps explain this difference and is often overlooked: the dew point. In this article we explain what the dew point is, how it relates to the way birds shed body heat, and how it can be used when assessing a race day.

1. What is the dew point?

The dew point is the temperature at which the moisture in the air begins to condense. If the air cools to this temperature it becomes saturated, and the moisture appears as water droplets. Morning dew on the grass, the fog you suddenly run into in a stream valley, and the drops collecting on the outside of a cold glass are all the result of the same thing.

Relative humidity expresses, as a percentage, how full the air is relative to its current temperature, and it changes constantly during the day along with the temperature. The dew point, on the other hand, directly shows how much moisture there actually is in the air. That is why it gives a more consistent answer to the question "how humid is it today?". The higher the dew point, the more moisture there is in the air.

You can see this in the loft too. In uninsulated metal-walled lofts, water collecting on the inside surfaces on cool, humid mornings happens because the metal surface cools below the dew point of the air inside. The birds' breathing and droppings also add moisture to the loft air; if ventilation is inadequate, this condensation becomes more pronounced.

2. How does a bird shed body heat?

Flight is work in which the breast muscles labour intensely and a great deal of heat is produced. The pigeon has to get rid of this heat; otherwise its body temperature rises and the bird is forced to slow down or stop.

Pigeons do not sweat like humans. They shed heat largely through evaporation: by evaporating water from the respiratory tract and the skin. The extensive air sac system connected to a bird's lungs keeps air flowing continuously through the respiratory tract during flight. A heat-stressed bird breathing fast with its beak open is the visible sign of this need to cool down.

How efficient evaporation is depends on the humidity of the air. If the air is dry, water evaporates easily and the bird sheds heat comfortably. If there is a lot of moisture in the air, evaporation slows down. Research on pigeons has shown that as humidity rises, the amount of water evaporated both through breathing and through the skin decreases. The bird can still cool down, but its margin narrows. Much of what fanciers describe as "the air was heavy" is exactly this: the air does not really become heavier, it becomes harder for the bird to shed its heat.

3. Same thermometer, different day

Let us compare two mornings:

	First morning	Second morning
Temperature	21 °C	28 °C
Dew point	20 °C	8 °C
Wind	Almost none	Light breeze
Appearance	Wet grass, fog in the hollows	Dry, clear weather

Someone looking at the thermometer might think the first morning is more comfortable. Yet on the first morning the air is almost saturated and it is hard for the birds to cool themselves by evaporation. Although the second morning is warmer, the air is dry; the birds usually fly more willingly. This may explain some cool mornings when, at exercise, the birds just will not climb and want to land on the roof after a short while.

Fog and a high dew point are not the same thing. Fog can form on a cool morning even with a low dew point. Fog is more a problem of visibility and orientation; a high dew point combined with heat is a problem of cooling and fatigue. On some days both come together; on those days there is no need to hurry the liberation.

4. A practical assessment scale

The ranges below are not scientifically established limits. They are a rough starting point, based on fanciers' observations, that can be used to add the dew point to your weather assessment:

Dew point	Assessment
Below 13 °C	Relatively dry air; generally favourable for evaporative cooling.
13–16 °C	Humidity rising; start watching it together with temperature, sun and wind.
16–18 °C	Humid; be more careful, especially as the temperature rises. Some experienced fanciers treat around 15–16 °C as their own warning line.
18–21 °C	Very humid; combined with strong sun, no wind, long distance or a headwind, the load increases markedly.
21 °C and above	A lot of moisture in the air; combined with a hot, long flight, conditions should be taken seriously.

Do not decide on the basis of a single number. A 19 °C dew point on a cool morning with a strong tailwind and a 19 °C dew point combined with 32 °C, full sun and a headwind are not the same day. Weather conditions act together.

5. Look at the whole route, not just the liberation site

A common mistake is to look only at the weather at the liberation site and at the loft. In middle- and long-distance races, birds pass through several different weather zones during the day. Air that is cool and dry at the morning liberation may be hot and humid in the middle of the route in the afternoon. Coastlines, large lakes, irrigated plains and areas under maritime influence (such as the Black Sea and Aegean coasts in Turkey) can raise humidity.

So on race day, looking at hourly forecasts of temperature, dew point, wind and cloud cover along the route gives a more accurate picture. A bird that will fly for seven hours races not in the weather at the moment of liberation but in the weather of the whole day. We explain the effect of wind on velocity in the race velocity article, and the liberation and homing window in the race day article.

6. Make observations with your own birds

The best way to understand the dew point's effect on your own birds is to keep records. For one month, note the following at every loft exercise: temperature, dew point, wind, sky conditions, how long the birds flew and how they behaved after landing. Look at how many birds are breathing with their beaks open after landing, how long they take to recover, and whether they go straight to the water.

Keep one distinction in mind: if a single bird in the team is struggling, look first at that bird's health and condition. If the whole team lands more distressed than you would expect from an ordinary flight, look at the weather before concluding that the team has suddenly lost condition. Good condition is the most important preparation against difficult weather; but condition does not change the weather.

It is also useful to compare your records with race results. Seeing how the winning velocity and the return rate in races over the same distance change on days with a high dew point helps you set a more realistic warning line for your own region.