iCloud sync high CPU on Mac (bird, cloudd, nsurlsessiond)

You opened Activity Monitor because the fans were up or the battery was draining, and near the top of the list is something cryptic: bird, or cloudd, or nsurlsessiond, using a lot of CPU. First, the reassuring part: none of these is a virus. Seeing bird high CPU on a Mac, or cloudd, or nsurlsessiond, almost always means iCloud is syncing, not that anything is wrong.

What bird, cloudd, and nsurlsessiond actually are

These aren't apps you installed. They're Apple's own background processes (daemons) that keep iCloud in sync, and they have deliberately obscure names, which is exactly why people search the exact one they saw:

• bird is the iCloud Drive daemon. It handles syncing files between your Mac and iCloud Drive, including your Desktop and Documents folders if you have that turned on.
• cloudd is the CloudKit daemon. It manages the broader iCloud sync that apps rely on: the data behind Notes, Reminders, Photos metadata, and third-party apps that store their data in iCloud.
• nsurlsessiond is the process that actually moves the bytes. It performs the background uploads and downloads over the network on behalf of iCloud (and some other system services).

So you can rule out the scary explanation early. Malware shows up as some other process with a name you don't recognize, not as the documented machinery of iCloud. High CPU here is your Mac doing the job you asked it to: keeping your files in two places at once.

Why bird is using high CPU on your Mac

Syncing is heavy work. To reconcile your Mac with iCloud, these processes have to read files, calculate what changed, compress and encrypt data, and push it up or pull it down over the network, all at once. A spike almost always traces back to something that gave iCloud a lot to move:

• A first sign-in or a new Mac. The initial sync after signing into iCloud, or after Migration Assistant, can churn for a long time as everything reconciles for the first time.
• A large Desktop & Documents sync. Turning on "Desktop & Documents Folders" hands iCloud potentially tens of gigabytes to upload, and bird and nsurlsessiond will work hard until it clears.
• A big upload or download. Adding a large folder, importing a photo library, or a shared album pulling files down all drive a burst of activity.
• "Optimize Mac Storage" moving files. When your disk gets tight, macOS offloads older iCloud files to the cloud and downloads them again on demand. That shuffling shows up as bird and nsurlsessiond activity.
• A stuck sync looping. Occasionally a single file gets wedged mid-transfer and the daemons retry it over and over, pegging CPU (and battery) without ever finishing. This is the one case worth acting on.

What's normal, and what isn't

• Normal: high bird / cloudd / nsurlsessiond CPU for a while during an active sync (after a sign-in, a big import, or turning on Desktop & Documents) that then settles and goes quiet. Large first syncs can take anywhere from many minutes to several hours on a slow connection. Let it run, ideally on power and Wi-Fi.
• Worth investigating: the processes sit pegged high for hours or days with no obvious sync happening, or the same activity spikes, calms, and spikes again on a loop. That points to a stuck transfer rather than real progress.

There's no official "normal percentage" here. Judge it by direction: is iCloud working through a backlog and trending toward done, or stuck in place while nothing is actually moving? This is also one of the processes worth checking when the fans are loud for no obvious reason, and a common answer to what's quietly draining your Mac's battery.

How to check whether it's really syncing

Before you touch anything, confirm there's a real sync in progress:

1. Open Activity Monitor (in Applications → Utilities), click the CPU tab, and type bird, cloudd, or nsurlsessiond into the search box to isolate them.
2. Open a Finder window and click iCloud Drive in the sidebar. Files still syncing show a small circular progress icon next to them. That's your proof the daemons are doing real work, and roughly how much is left.
3. Check the overall status at System Settings → [your name] → iCloud. It shows your iCloud storage and whether a sync or upload is underway.

If the Finder shows files actively progressing, the answer is usually to leave it alone. If nothing appears to be moving yet CPU stays high, you likely have a stuck sync.

What to do (without force-quitting)

Work from gentlest to most drastic. Note upfront: quitting bird or cloudd in Activity Monitor doesn't help. They're core system daemons and relaunch instantly, so repeatedly force-quitting just restarts the same stuck job.

• Let a real sync finish. Most of the time this is the right answer. Plug into power, stay on Wi-Fi, and give a large first sync an hour or two before checking again.
• Pause iCloud Drive briefly, then resume. If it's been stuck for hours, go to System Settings → [your name] → iCloud → iCloud Drive and turn off Sync this Mac. Wait a minute, then turn it back on. This often nudges a wedged transfer loose. macOS may ask whether to keep local copies while it's off, and keeping them is fine.
• Sign out and back into iCloud (the classic fix). If pausing doesn't clear it, go to System Settings → [your name], scroll down, and click Sign Out, then sign back in after a minute. This rebuilds the local sync state and reliably clears a stuck one. The caveat: signing out removes the local copies of your iCloud Drive files from this Mac (they stay safe in iCloud), so they have to re-download afterward, which means another round of bird and nsurlsessiond activity right after you sign back in. Make sure the files you need offline have finished downloading before you rely on it.

What not to do: don't disable iCloud entirely as a first move to "stop the CPU." You'd trade a temporary, self-resolving sync for turning off the feature that keeps your files backed up and available across devices. If a different process is actually at the top of the list, this family has siblings. mds_stores and Spotlight indexing spike for their own reasons after big file changes, often right alongside an iCloud sync.

By the time you've opened Activity Monitor, the frustrating part is that you still can't tell whether bird is making real progress or stuck in a loop, or whether iCloud is the actual cause of the heat or just one of several busy processes. Plumby keeps a live readout of CPU, memory, and network in your menu bar and holds that history across reboots, so you can see whether an iCloud sync is trending down and finishing or stuck, and which process is really driving the spike. It names the cause in plain words and flags when a reading is simply normal under load, so a loud fan points you to the true culprit instead of a virus that was never there.