Concerted Effort...comment ça marche exactement?

Concerted Effort
%2 %W %W
Enchantment
At the beginning of each upkeep, all creatures you control gain flying until end of turn if a creature you control has flying. The same is true for fear, first strike, double strike, landwalk, protection, trample, and vigilance.

Giant Slug
%1 %B
Creature — Slug
1/1
%5 : At the beginning of your next upkeep, choose a basic land type. Giant Slug gains landwalk of the chosen type until the end of that turn

Grizzly Bears
%1 %G
Creature — Bear
2/2

Si j'active sa capa pendant le tour adverse (disons choix = île) et que j'ai pour seule autre créature un Grizzly Bears, je pense que le pauvre ours n'apprendra pas à nager ce tour-ci car la capacité ne s'est pas déclenchée.

Mais si j'ai aussi en jeu une créature avec le vol, que se passe-t-il?

*Extra*: The Effort's trigger doesn't know what it's going to give to your creatures until it resolves. Giving critters abilities or stealing critters can change the who and what happens with the Effort. For instance, if in response to the trigger you lose control of a flier but gain control of a double striker, all the creatures you control as the ability resolves will share that double strike.

Concerted Effort
%2 %W %W
Enchantment
At the beginning of each upkeep, all creatures you control gain flying until end of turn if a creature you control has flying. The same is true for fear, first strike, double strike, landwalk, protection, trample, and vigilance.

404.3. A triggered ability may read “When/Whenever/At . . . , if [condition], [effect].” The ability checks for the stated condition to be true when the trigger event occurs. If it is, the ability triggers. On resolution, the ability rechecks the condition. If the condition isn’t true at either of those times, the ability does nothing. This rule is referred to as the “intervening ‘if’ clause” rule. Note that the word “if” has only its normal English meaning anywhere else in the text of a card; this rule only applies to an “if” that immediately follows a trigger condition.