Squirrels think they're candy. Or if the bulb is mushy all or in part, could be bulb flies. The latter would be very unusual if you planted them this past fall.

Although others have mentioned this problem as well I don't remember encountering squirrels spoiling tulips myself - and 1 in. tunnels in the ground would not be those anyway. Slugs may gnaw tulips, including the bulbs under moist conditions. Deer will snip the flowers off and leave the flower stems and leaves standing there, looking somewhat pointless.

What squirrels are murder on is crocuses. When they get into those you can tell it's them because you find the sprouts and the tunics (skins) lying on the ground with no corms left - or maybe some fragments.

Daffodils are poisonous and therefore recommended for planting in places deer frequent but this toxicity does not stop slugs from sliming up the stalks and destroying the flowers during damp weather. This is such a pervasive problem that annual routine baiting to prevent the display being ruined seems necessary on many sites.

Wild tulips come from open places in semiarid climates, in gardens they do best in similar conditions: clean ground with plenty of exposure and no litter to harbor slugs or significant shading from shrubs and trees. (Trees and shrubs, of course, may also harbor squirrels).

If animals are around they will always be looking for food and have no qualms about helping themselves to any plants that you present them with that are tasty to them. City gardens have fewer unwanted guests than in the suburbs/country, where you may have to install secure fencing and take other measures in order to have a satisfactory gardening experience. With deer and rabbits in particular you are really leaving yourself open to recurring disappointment if these are not effectively excluded.

Susceptible kinds of bulbs may need to be planted inside of wire mesh to prevent them being attacked beneath the soil surface or pulled out of the ground.

It sounds like voles. I don't know how to control them. Try Google.

If you put a large board down on the ground and after a few weeks the ground underneath is honeycombed with tunnels at the surface, you have voles. I have had fewer daylilies eaten after putting lava rock in the bottom and sides of planting holes. They like deep mulch and ground covers. Voles are native American rodents related to lemmings, and have stocky bodies and tails half the length of their bodies.

Interplanting poisonous (daffodils) and untasty (iris, species tulips) plants with tastier bulbs can help, or put the tulips in pots.

FYI Moles are carnivores. They eat worms and grubs not plant material.

Daffodils do better here in the NW as far as naturalizing and persisting year after year. Many tulips die out after a few years, they don't like our clay soils. Species tulips do well in rock gardens though. I've got some that are over ten years old about to bloom in my fake rock garden along the south curb.

It was said: "I don't remember encountering squirrels spoiling tulips myself "

Well put it this way.

When I first arrived in Portland, OR, I thought I'd do a favor for my son & his wife. I planted lots of tulips, also daffodils.

I visited about a week later. The squirrels had "harvested " all the tulips but none of the daffodils.

Voles!

Squirrels eat tulips like candy. I have read that mixing daffodils and alliums in the tulip bed can deter them. I have no success. I have personally witnessed the darn squirrels digging up and chowing down on tulips. Then burying the leftovers. Maybe Tulips needs to be planted deeper in the ground than recommended too. There are some in our garden that have been there since before we moved here which are planted more than 10 inches deep.

It's voles. I don't know how to control them either. I had a garden where I'd planted nearly 500 bulbs of all kinds in the space of 3 years - daffodils primarily, also narcissus, species crocus, species tulips, snowdrops, grape hyacinths. Nearly all the daffodils had disappeared within 2 years of planting. No clay in that soil, I don't know what you're talking about buyorsell when you say that "our" PNW soils are clay, yours may be but Puget Sound soils are largely gravel and sand. I wish I had some clay, things wouldn't dry out so fast.

Anyway the crocus were fine, and the snowdrops and the grape hyacinth, but only some of the species tulips and narcissus lasted and of the daffodils only the ones closest to the house lasted. I blame voles. The dogs patrolled better closer to the house. Then again, one of my hiking trails passes what was a homestead but has been abandoned for 60 years now, and there's still lots of daffodils coming up. Plenty of voles there too. So who knows.

yes, squirrels do dig up and eat bulbs of all kinds, but your description sounds like voles, with the horizontal tunnels and all.

My pest control guy who sprays for carpenter ants has setup rodent traps that look like little houses that rats/voles crawl into and eat the poison. This may be one way to kill voles without having any poisons exposed to pets/kids. My only concern with this is killing squirrels which I do like. I have seen squirrels dig up some bulbs but it is pretty rare. I have some bird feeders around and they do a nice job of cleaning up the bird seed that the birds flick on the ground so they save me the work of cleaning it up. I see them eating under the bird feeders a lot.

Of the four places I've lived in this area, three had clay. Only my current place has sand. That's not exactly scientic sampling, but my experience would have lead me to think clay was more common.

I live on a hill (much of the pnw is hills) and we have very sandy soil. My fiance's parents' house has sand soil, and growing up in Olympia we had sandy soil too. All were located on or near hills.