We are all aware, (or should be) that the birds of teir, namely Swellow and Braviary (And Fearow, which is a hybrid of the two) are everywhere at the moment. And just like Zapdos in RBY they have made it nearly impossible to make a team without a rock type to reliably switch in. Teams without a way to deal with the birds will commonly find themselves having to sacrifice a Pokemon or play very accurate prediction games, which is undesirable in the long term.
Good preparation is key and while they may seem like demons in the tier you do have options at your disposal to make sure that you aren't wrecked by the winged terrors.
First and foremost is Stealth Rock. I don't feel like I need to go over this heavily as for it overlaps with the Pokemon section. That said keeping Stealth Rocks on the field will severly hamper how much damage the birds can do to your team. Swellow especially as a result of the added recoil from carrying a status orb.
However, relying on Stealth Rocks as your sole way of dealing with the birds is a futile endeavor. They will punch holes without any way for you to stop them and while they might not sweep you. Their teammates will. So what can we do?
The answer is to carry a Pokemon that can tank their attacks. More often than not this will require you to take a Pokemon that resists both Flying and Normal. The only two types that can do this are Steel and Rock. And with the recent tier shifts good Steel Types are few and far between. But do not fear, for I am here to show you want options are available to you.
Regirock
By far the most common answer to the birds and definitely a staple on alot of NU teams, especially in the current meta. It can tank hits from the birds all day. Swellow can't beat it on it's own and Braviary needs it to be weakened to KO it with Superpower (A common theme.)
What does it have over the other options?
80 / 200 / 100 Are simply amazing defenses. It can tank hits all day with very little investment as well as having the flexibility to switch EVs to SDef to check common special attackers such as Rotom and Magmortar. While Probopass and Bastiodon may boast higher special defenses Regirock has much more reliable damage outputs over them.
Probopass
Another common answer to the birds of NU. It's dual Steel and Rock typing means it takes next to nothing from their STAB attacks and has a plethora of moves it can use to deal with the birds. However the Steel/Rock typing is a double edged sword as it makes it very susceptible to Braviary's Superpower and Fearow's Drill Run.
What does it have over the other options?
Probopass is perhaps the most versatile options in so far as it has the most support options for the rest of the team. It is also the best option for gaining momentum through it's access to volt switch. In addition it is pretty much the only option that hits on the special side of the spectrem giving it yet another thing that makes it differ from the competition.
Bastiodon
Very similar stats wise to Probopass without the special attack options. As a result it does well against the birds for the same reasons as Probopass does.
What does it have over the other options?
Perhaps the only thing that sets it apart is it's combination of Taunt / Metal Burst and the ability sturdy meaning it is able to function as a very good surprise killer for other threats in the tier. However as a one trick pony this is usually easy to pick up on and thus countered. That said it is a viable option and can turn matches in your favour if used correctly under the correct conditions.
Golem
Golem rounds out the trio of the the top three most popular answers to the birds.
What does it have over the other options?
Golem has dual STAB on EdgeQuake and a large attack stat meaning it can hit very hard. In addition it gains access to Sucker Punch allowing it to function well against non Sub Gorebyss which is usually a pain for pokemon of it's type. One of the best options for offensive teams.
Relicanth
Another strong offensive option to deal with bird. In addition it can both counter birds and run a sweeping set at the same time.
What does it have over other options?
Another interesting dual stab that sets it apart from the other options for this role. He hits incredibly hard with STAB Head Smash as well as set up on birds that are stuck in a move that isn't super effective or named Swellow. This can be a great boon for your team thus making it another great choice for offensive teams.
*work in progress*
To come: Lairon, Metang, Bronzor, Gigalith, Luxray, Golbat, Alomomola
Good preparation is key and while they may seem like demons in the tier you do have options at your disposal to make sure that you aren't wrecked by the winged terrors.
First and foremost is Stealth Rock. I don't feel like I need to go over this heavily as for it overlaps with the Pokemon section. That said keeping Stealth Rocks on the field will severly hamper how much damage the birds can do to your team. Swellow especially as a result of the added recoil from carrying a status orb.
However, relying on Stealth Rocks as your sole way of dealing with the birds is a futile endeavor. They will punch holes without any way for you to stop them and while they might not sweep you. Their teammates will. So what can we do?
The answer is to carry a Pokemon that can tank their attacks. More often than not this will require you to take a Pokemon that resists both Flying and Normal. The only two types that can do this are Steel and Rock. And with the recent tier shifts good Steel Types are few and far between. But do not fear, for I am here to show you want options are available to you.

Regirock
By far the most common answer to the birds and definitely a staple on alot of NU teams, especially in the current meta. It can tank hits from the birds all day. Swellow can't beat it on it's own and Braviary needs it to be weakened to KO it with Superpower (A common theme.)
What does it have over the other options?
80 / 200 / 100 Are simply amazing defenses. It can tank hits all day with very little investment as well as having the flexibility to switch EVs to SDef to check common special attackers such as Rotom and Magmortar. While Probopass and Bastiodon may boast higher special defenses Regirock has much more reliable damage outputs over them.

Probopass
Another common answer to the birds of NU. It's dual Steel and Rock typing means it takes next to nothing from their STAB attacks and has a plethora of moves it can use to deal with the birds. However the Steel/Rock typing is a double edged sword as it makes it very susceptible to Braviary's Superpower and Fearow's Drill Run.
What does it have over the other options?
Probopass is perhaps the most versatile options in so far as it has the most support options for the rest of the team. It is also the best option for gaining momentum through it's access to volt switch. In addition it is pretty much the only option that hits on the special side of the spectrem giving it yet another thing that makes it differ from the competition.

Bastiodon
Very similar stats wise to Probopass without the special attack options. As a result it does well against the birds for the same reasons as Probopass does.
What does it have over the other options?
Perhaps the only thing that sets it apart is it's combination of Taunt / Metal Burst and the ability sturdy meaning it is able to function as a very good surprise killer for other threats in the tier. However as a one trick pony this is usually easy to pick up on and thus countered. That said it is a viable option and can turn matches in your favour if used correctly under the correct conditions.

Golem
Golem rounds out the trio of the the top three most popular answers to the birds.
What does it have over the other options?
Golem has dual STAB on EdgeQuake and a large attack stat meaning it can hit very hard. In addition it gains access to Sucker Punch allowing it to function well against non Sub Gorebyss which is usually a pain for pokemon of it's type. One of the best options for offensive teams.

Relicanth
Another strong offensive option to deal with bird. In addition it can both counter birds and run a sweeping set at the same time.
What does it have over other options?
Another interesting dual stab that sets it apart from the other options for this role. He hits incredibly hard with STAB Head Smash as well as set up on birds that are stuck in a move that isn't super effective or named Swellow. This can be a great boon for your team thus making it another great choice for offensive teams.
*work in progress*
To come: Lairon, Metang, Bronzor, Gigalith, Luxray, Golbat, Alomomola